Principles of Mechanical Ventilation

CHAPTER © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 3NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC PrinciplesNOT FOR SALE OR DISTRIBUTION of MechanicalNOT FOR SALE OR DISTRIBUTION Ventilation © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOTGregory FOR SALE A. OR Holt, DISTRIBUTION Sheila A Habib, andNOT David FOR SALE C. Shelledy OR DISTRIBUTION © Thep © Thep Urai/Shutterstock © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

OUTLINE Complications of Mechanical Ventilation Pulmonary Introduction to Mechanical© Ventilation Jones & Bartlett Learning, LLCExtrapulmonary Organ Systems © Jones & Bartlett Learning, LLC Ventilation NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Spontaneous Breathing Negative Pressure Breathing OBJECTIVES Positive Pressure Breathing 1. Summarize the history of events that led to modern Invasive Versus Noninvasive Ventilation mechanical ventilation. Ventilator Principles © Jones & Bartlett Learning, LLC 2. Contrast© the Jones differences & betweenBartlett positive Learning, and negative LLC Input Power and Control Systems pressure ventilation. VentilatorNOT Variables:FOR SALE Breath Trigger OR DISTRIBUTION 3. RecognizeNOT differences FOR inSALE patient interface OR DISTRIBUTION when considering Ventilator Variables: Breath Cycle invasive and noninvasive mechanical ventilation. Operator Interface 4. Define the timing points that constitute a breath and Ventilator Classification or Taxonomy calculate the respiratory rate from TI and TE. Ventilator Modes 5. Describe alveolar and dead space ventilation and calculate Continuous Mandatory Ventilation V˙ E and V˙ A. © Jones & BartlettIntermittent MandatoryLearning, Ventilation LLC © Jones6. Interpret& Bartlett changes Learning, in volume, airflow, LLC and alveolar and NOT FOR SALEPositive OREnd-Expiratory DISTRIBUTION Pressure NOT FORintrapleural SALE pressure OR DISTRIBUTION over the course of a single breath. Continuous Positive Airway Pressure 7. Describe the differences between an iron lung and a chest Pressure Support Ventilation cuirass. Airway Pressure Release Ventilation 8. Identify the components of a ventilator circuit and the Automatic Tube Compensation mechanical events during lung inflation and deflation during Proportional Assist Ventilation delivery of a positive pressure breath. Dual Modes and Adaptive© Control Jones & Bartlett Learning, LLC9. Describe the effects of alterations© Jones in lung mechanics& Bartlett Learning, LLC High-Frequency Ventilation NOT FOR SALE OR DISTRIBUTION(CST and Raw) on volume andNOT pressure FOR in volume SALE and OR DISTRIBUTION Neurally Adjusted Ventilatory Assist pressure-control modes. Ventilator Parameters 10. Predict changes in peak inspiratory pressure and plateau Flow Waveforms pressure when either CST or Raw are altered. Inspiratory Pause 11. Define PEEP and describe its influence on gas exchange and Fio2 hemodynamics. PEEP/CPAP© Jones & Bartlett Learning, LLC 12. Describe© theJones variables & of Bartlett interest in an Learning, optimal PEEP study. LLC Alarms 13. Define pressure support ventilation (PSV) and describe its HumidificationNOT FOR SALE OR DISTRIBUTION influenceNOT on the FOR work ofSALE breathing OR (WOB). DISTRIBUTION Sigh Breaths 14. Define CPAP, BiPAP, AutoPAP, ASV, CFLEX, EPR, IPAP, Effects of Mechanical Ventilation on Organ Systems and EPAP. Pulmonary System 15. Describe patient scenarios that will lead to increased mean Cardiovascular System airway and peak inspiratory pressures. Renal System © Jones & Bartlett Learning, LLC © Jones16. Describe& Bartlett the variables Learning, that can be LLC trigger inspiration during Gastrointestinal System mechanical ventilation. NOT FOR SALECentral NervousOR DISTRIBUTION System NOT FOR SALE OR DISTRIBUTION

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17. Describe the variables that can cycle a breath from breath cycle oxygen saturation in mixed – © Jones & Bartlettinspiration Learning, to expiration. LLC © Jonesbreath &trigger Bartlett Learning,venous LLC blood (Svo2) NOT FOR SALE18. Contrast OR DISTRIBUTIONthe differences between PC-AC and VC-AC. NOTcontinuous FOR SALE positive OR airway DISTRIBUTION partial pressure of alveolar 19. Contrast the differences between PC-IMV and VC-IMV. pressure (CPAP) oxygen (Pao2) 20. Describe the rationale for prone positioning ARDS patients. dead space volume (VD) partial pressure of arterial 21. Describe lung protective strategies for mechanical ventilation. expiratory positive airway oxygen (Pao2) 22. Define APRV and compare this mode to BiPAP. pressure (EPAP) partial pressure of mixed – 23. Describe the use of automatic tube compensation (ATC). expiratory time (TE) venous oxygen (Pvo2) 24. Define PAV and describe© Jones its use. & Bartlett Learning, LLCextrinsic PEEP ©peak Jones airway & pressure Bartlett (Paw Learning,) LLC 25. Identify dual modesNOT of ventilation. FOR SALE OR DISTRIBUTIONflow cycle NOTpeak inspiratoryFOR SALE OR DISTRIBUTION 26. Define PRVC and VAPS. flow-time scalar pressure (PIP)

27. Describe each of the four types of high-frequency ventilation fraction of inspired plateau pressure (Pplateau) (HFV). oxygen (Fio2) positive end-expiratory 28. Contrast the trigger variable used in NAVA to conventional high-frequency jet pressure (PEEP) mechanical ventilation. ventilation (HFJV) positive pressure ventilation 29.© DescribeJones inspiratory & Bartlett flow waveforms Learning, used in LLC mechanical high-frequency© Jonesoscillatory & Bartlettpreload Learning, LLC NOTventilation. FOR SALE OR DISTRIBUTION ventilationNOT (HFOV) FOR SALEpressure OR DISTRIBUTIONcontrol (PC) 30. Determine the ventilator variables that affect Pao2, pH, high-frequency percussive pressure-regulated volume and Paco2. ventilation (HFPV) control (PRVC) 31. Identify the alarms that require clinician adjustment and the high-frequency pressure support levels of priority assigned. positive pressure ventilation (PSV) 32. Describe the rationale for a sigh breath. ventilation (HFPPV) pressure–time scalar © Jones & 33.Bartlett Explain Learning, the effects of positive LLC pressure ventilation © Joneshyperventilation & Bartlett Learning,proportional LLC assist on the lung. hypoventilation ventilation (PAV) NOT FOR SALE34. Explain OR the DISTRIBUTION effects of positive pressure ventilation on the NOTinspiratory FOR SALE positive OR airway DISTRIBUTION pulmonary vascular cardiac/cardiovascular system. pressure (IPAP) resistance (PVR)

35. Describe the central nervous system (CNS), renal, and inspiratory time (TI) synchronized intermittent gastrointestinal effects of positive pressure ventilation. inspiratory to expiratory mandatory 36. Explain the importance of appropriate sedation protocols ratio (I:E) ventilation (SIMV) during weaning from© mechanicalJones & ventilation. Bartlett Learning, LLCintracranial pressure (ICP) ©tidal Jones volume & (V BartlettT) Learning, LLC 37. Describe the influence of Paco2 on intracranial intrinsic PEEP time cycling pressure (ICP). NOT FOR SALE OR DISTRIBUTIONiron lung NOTtotal cycleFOR time SALE (Ttot) OR DISTRIBUTION 38. Identify the effects of sleep disruption on the ICU patient. lung compliance (CL) transmural wall pressure 39. List the complications of mechanical ventilation and mean airway pressure ventilator-associated explain each. (MAP) lung injury (VALI) minute alveolar volume ventilator-associated ˙ KEY TERMS minute ventilation (VE) pneumonia (VAP) © Jones & Bartlett Learning, LLC negative pressure© Jones & Bartlettventilator-induced Learning, LLC acidosisNOT FOR SALE OR DISTRIBUTIONatelectotrauma ventilationNOT FOR SALE lungOR injury DISTRIBUTION (VILI) acute lung injury (ALI) atrial natriuretic neurally adjusted ventilator mode acute respiratory distress peptide (ANP) ventilatory assist (NAVA) volume-assured pressure syndrome (ARDS) automatic positive noninvasive positive support (VAPS) afterload airway pressure pressure ventilation volume control (VC) airway pressure release (autoPAP) (NPPV) volume of carbon dioxide ˙ © Jones & Bartlettventilation Learning, (APRV) LLCautomatic servo © Jonesoxygen & content Bartlett in Learning,production LLC (VCO2) airway resistance (Raw) ventilation (autoSV) arterial blood (Cao2) volume of oxygen NOT FOR SALEalkalosis OR DISTRIBUTIONautomatic tube NOToxygen FOR contentSALE in OR mixed DISTRIBUTION uptake (V˙O ) – 2 alveolar volume compensation (ATC) venous blood (CVo2) volume support (VS) amyotrophic lateral autoPEEP oxygen delivery (D˙ o2) volutrauma sclerosis (ALS) bilevel positive airway oxygen saturation in work of breathing (WOB)

assist control (A/C) pressure (BiPAP) arterial blood (Sao2) © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Introduction to Mechanical was offered by John Emerson in 1932. In the 1940s and Ventilation 1950s, polio epidemics were sweeping across Europe © Jones & Bartlett Learning, LLC and the United© Jones States. Worldwide,& Bartlett 500,000 Learning, people perLLC The development of respiratory care progressed year were either paralyzed or had died from the dis- throughNOT history FOR fromSALE Galen’s OR observationsDISTRIBUTION on the re- ease.1 TheseNOT negative FOR pressure SALE ventilators OR DISTRIBUTION were some- spiratory and circulatory systems in the 2nd century to times employed in large halls dedicated to providing the early 20th century, when great strides in pulmonary support to polio victims (Figure 3-1). The iron lung did physiology were made. The Drinker Respirator, which not require an artificial airway and was simple and easy negative pressure ventilation © Jones & providedBartlett Learning, LLC , was introduced© Jonesto use. & Problems Bartlett included Learning, difficulty LLC with patient access, in 1928, and a commercial version of this “iron lung” patient immobility, and large and bulky equipment. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

9781284139860_CH03_095_154.indd 96 21/02/19 5:37 PM Introduction to Mechanical Ventilation 97

Fig©ure Jones 3-1 The Iron& Bartlett Lung in Use DuringLearning, the Polio Epidemic.LLC © Jones & Bartlett Learning, LLC TOP:NOT ©Dennis MacDonald/ageFOR SALE fotostock/Alamy OR Stock DISTRIBUTION Photo; BOTTOM: ©Science History NOT FOR SALE OR DISTRIBUTION Images/Alamy Stock Photo.

In 1952, a polio outbreak in Copenhagen (following Figure 3-2 Bird and Bennett Pressure Respirators. The Bennett © Jones & aBartlett 1951 international Learning, convention LLC on polio) resulted in 50© JonesPR-2 was & time Bartlett or patient Learning,triggered to inspiration, LLC pressure limited, new admissions every day and an 87% mortality rate. and flow cycled to expiration. The Bird Mark 7 was time or patient NOT FOR SALEMedical OR students DISTRIBUTION were called upon, and nearly 1500 NOTtriggered FOR toSALE inspiration OR and DISTRIBUTION pressure cycled to expiration. provided manual bag-mask positive pressure ventilation totaling 165,000 hours with a drop in mortality to approximately 25%.2 The development of the modern these new ventilators over the “iron lung.” The volume intensive care unit (ICU)© Jones providing & Bartlettmechanical Learning, ventila- LLCventilators of the 1960s and early© Jones 1970s allowed& Bartlett cli- Learning, LLC tory support can be traced directly to the impact of this nicians to set a precise tidal volume (VT) and backup single disease, polio.NOT FOR SALE OR DISTRIBUTIONrespiratory rate to guarantee NOTa minimum FOR minute SALE venti OR- DISTRIBUTION The use ofpositive pressure ventilation grew lation. It took longer to understand the mechanisms of along a similar timeline and rapidly became the pre- ventilator-induced lung injury and the balance between dominant form of ventilatory support in use. Patient- atelectasis, pulmonary overdistension, and barotrauma. ventilator-induced lung injury (VILI) triggere© Jonesd, pressure-cycled & Bartlett ventilators Learning, (e.g., LLC Bird The mechanisms© Jones of & Bartlett Learning, LLC respirators) and flow-sensitive breathing valves (e.g., are due, in part, to the release of cellular inflammatory theNOT Bennett FOR valve) SALE based ORon technology DISTRIBUTION developed dur- mediators associatedNOT FOR with SALE the use OR of large DISTRIBUTION tidal volumes ing World War II were further developed in the 1950s and pressures. This has led to a reduction inapplied and 1960s (Figure 3-2). Volume ventilators began to tidal volumes from 10 to 15 mL/kg used since the become available, first as time-triggered devices, and mid-1970s to the 4 to 8 mL/kg currently employed.3,4 © Jones & laterBartlett with patient-triggered Learning, LLC options. Space require- © JonesAdditional & Bartlett methods Learning, to reduce ventilator-associated LLC ments and patient access were obvious advantages of lung injury include appropriate application NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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© Jones &of Bartlett positive end-expiratoryLearning, LLC pressure (PEEP), lung re- © Jones & Bartlett Learning, LLC T T cruitment strategies, permissive hypercapnia, the introNOT- FOR SALEI OR DISTRIBUTIONE NOT FOR SALEduction ORof newer DISTRIBUTION modes of pressure limited ventilation, and the addition of noninvasive ventilation (NIV) to 2 4 0 the decision tree for respiratory-compromised patients.

The mechanical ventilator of the 21st century em- (L/m) Flow 6 T ploys sophisticated technology© Jones to & detect Bartlett and shape Learning, LLC tot © Jones & Bartlett Learning, LLC the breath with sensitivityNOT andFOR responsiveness SALE OR provid- DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ing clinicians with a myriad of control features. The Time (sec) goal of mechanical ventilation continues to be support of the oxygenation and ventilation of patients in Figure 3-3 Determination of Respiratory Cycle Time Using a respiratory failure. The resolution of the underlying Flow–Time Curve. Here, the inspiratory time (TI) is 2 seconds, the disease process, the anticipated timing of resolution, expiratory time (TE) is 4 seconds, and the total cycle time (Ttot) is © Jones & Bartlett Learning, LLC 6 seconds. The© T Jonescontinues as& long Bartlett as inspired Learning, flow is above 0. LLC T and the expected outcomes guide the type of me- I E NOT FOR SALE OR DISTRIBUTION begin at the endNOT of TI and FOR continues SALE to the ORnext inspiredDISTRIBUTION breath. chanical ventilation and delivery interface selected. Data from Creative Media Services, UT Health. For example, a patient with an acute exacerbation of congestive heart failure (CHF) may benefit from noninvasive positive pressure ventilation (NPPV) via BOX 3-1 Components of the Breath © Jones & fullBartlett face mask Learning, until pharmacologic LLC agents have had a © Jones & Bartlett Learning, LLC chance to produce favorable outcomes. A patient with The timing of a single breath is divided into NOT FOR SALEamyotrophic OR DISTRIBUTIONlateral sclerosis (ALS) NOT FOR SALE OR DISTRIBUTION requiring long-term the time for inspiration (TI) and the time for care may elect tracheostomy and continuous full ven- exhalation (TE). tilatory support. Engineers developing these devices work closely with physiologists, pulmonary physicians, The total cycle time (Ttot) is given by the equation: and respiratory therapists© Jones to match & Bartlettfunction to Learning, the pa- LLC Ttot = T©I + Jones TE & Bartlett Learning, LLC thologies before them. The purpose of this chapter is NOT FOR SALE OR DISTRIBUTIONThe inspiratory to expiratoryNOT ratio FOR is expressed: SALE OR DISTRIBUTION to introduce the principles of mechanical ventilation to the reader. I:E

For example, if TI = 2 seconds and TE = 4 seconds, Ventilation then Ttot = 6 seconds, or © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 6 sec = 2 sec + 4 sec TheNOT primary FOR function SALE of theOR respiratory DISTRIBUTION system is to NOT FOR SALE OR DISTRIBUTION ensure adequate tissue oxygenation and carbon dioxide The I:E ratio is 2 : 4 or reduced, 1 : 2, and the respira- removal. Ventilation is cyclic in nature and composed of tory rate (f) is given by the equation: an inspiratory and expiratory phase whereby volumes of 60 60 10 breaths alveolar gas are moved from ambient air to the alveoli f 5 5 5 Ttot 6 min © Jones & andBartlett back. The Learning, gases of interest LLC are nitrogen, oxygen, © Jones & Bartlett Learning, LLC and carbon dioxide. Dependent on the fuel substrate for NOT FOR SALEATP production OR DISTRIBUTION and the general health of the individual,NOT FOR SALE OR DISTRIBUTION ˙ volume of oxygen uptake (VO2) and volume of carbon zero. In mechanical ventilation, it is important to under- dioxide output (V˙CO2) are normally about 250 mL O2/ stand the timing of the ventilatory cycle and its relation- min and 200 mL CO2/min. Nitrogen, an inert gas, gener- ship with the inspiratory-to-expiratory ratio (I:E ratio) Box 3-1 ally does not cross the© alveolar-capillary Jones & Bartlett (AC) membrane Learning, LLC( ). © Jones & Bartlett Learning, LLC to any appreciable degree unless the subject is exposed to Ventilation can be defined as the bulk movement higher than atmosphericNOT pressures. FOR SALE OR DISTRIBUTIONof gas into and out of the lungs.NOT A normal FOR adultSALE tidal OR DISTRIBUTION The ventilatory cycle combines a single inspired vol- volume (VT) is about 500 mL (range 400–700 mL) or ume of air with a single expired volume of air. The time 7 mL/kg of ideal body weight (IBW, aka predicted body it takes for this event is termed the total cycle time. The weight [PBW]). A normal adult respiratory rate (f) is total© cycleJones time & (T Bartletttot) is equal Learning, to the inspiratory LLC time (TI) about 12 breaths/min© Jones (range & Bartlett 12 to 20) Learning, and a normal LLC expiratory time (T ) = + minute ventilation (V˙ E) plusNOT the FOR SALE ORE where DISTRIBUTION Ttot TI TE. adult NOT FOR SALE is about OR 6 DISTRIBUTIONL/min (range 5 to The inspiratory time occurs when inspiratory gas flow 10 L/min), where: moves from zero to peak and back to zero at the end of V˙ = V × f = 500 mL/breath × 12 breath/min inspiration (Figure 3-3). The expiratory time begins at E T = 6000 mL/min or 6 L/min the end of inspiration with airflow at zero and continues © Jones & untilBartlett the start Learning, of the next LLCinspiratory cycle. Generally, © JonesOnly & about Bartlett 70% of Learning, the inspired V LLCT will reach the alveoli the expiratory time is longer than inspiratory time and to participate in gas exchange, and this is the alveolar NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ˙ may include a brief pause with airflow remaining at ventilation per breath (VA) and per minute (VA) (Box 3-2).

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© Jones & Bartlett Learning, LLC © Jonesinspiration & Bartlett and exhalation Learning, during LLCquiet breathing pass BOX 3-2 Minute Ventilation and Alveolar without conscious awareness. The timing of inspiration NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Ventilation and exhalation will vary from moment to moment, dependent on sleep/wake state and activity. The inspired Minute exhaled ventilation (V˙ E) is given by the flow rate will also vary, but given a VT of 500 mL/breath equation: and an inspiratory cycle time of 1 second, the average © VJones˙ E= f × V &T Bartlett Learning, LLCinspired flow rate is 0.5 L/sec© and Jones extrapolated & Bartlett to Learning, LLC 1 minute, 30 L/min. Minute alveolar ventilationNOT FOR (V˙ A) SALEis given byOR the DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Voluntary (cortical) control of breathing is asserted equation: during many normal activities, including laughing, V˙ A = f × (VT – VD) singing, speaking, and playing a wind instrument. For example, if f = 12 breaths/min, V = 500 mL/ Larger-than-normal tidal volumes and flow rates T occur with cough, sneeze, sigh, and extremes of arterial breath© Jones and V & = Bartlett 150 mL/breath, Learning, then: LLC © Jones & Bartlett Learning, LLC D acidosis or exercise. These flow rates, tidal volumes, and NOT FOR SALE OR DISTRIBUTION6000 ml 6 L NOT FOR SALE OR DISTRIBUTION V˙ = f × V = 12 × 500mL = = inspiratory/expiratory times are the result of central E T min min nervous system (CNS) outflow, either autonomic or under conscious control. When cortical and/or medul-

V˙A = f × (VT – VD) = 12 (500 – 150) lary centers produce an inspiratory activating signal, a series of action potentials first encounters the phrenic © Jones & Bartlett Learning,4200 LLC mL 4.2 L © Jones & Bartlett Learning, LLC = or motoneurons of the cervical spinal cord between the NOT FOR SALE OR DISTRIBUTIONmin min NOT FOR SALE OR DISTRIBUTION third and fifth cervical vertebrae and travel down the right and left phrenic nerve. These nerves innervate the right and left hemidiaphragm. When contraction is initiated, the diaphragm descends towards the abdomi- The remaining 30% (about 150 mL/breath) fills the nal cavity. The degree of motion is dependent on the conducting airways, ©which Jones extend & fromBartlett the external Learning, LLC © Jones & Bartlett Learning, LLC level of activation. nares down to (and including)NOT FOR the SALEterminal OR bronchioles. DISTRIBUTION NOT FOR SALE OR DISTRIBUTION When the diaphragm contracts and descends, there The volume of gas in the conducting airways is about is a decrease in the intrapleural and intrathoracic 1ml/lb IBW and represents the anatomic dead space pressures. During quiet respiration, the intrapleural (V ). There may also be alveoli that are ventilated but D ant pressure may range from –5 cm H O at passive end not perfused and the is the alveolar dead space (V ). 2 D alv expiration to –10 cm H O during inspiration. This Physiologic© Jones dead & spaceBartlett (V Learning,) is simply V LLC+ V , © Jones 2& Bartlett Learning, LLC D phys D ant D alv 5-cm H O pressure change, when coupled with normal whichNOT represents FOR SALE all the inspired OR DISTRIBUTION gas that does not 2 NOT FOR SALE OR DISTRIBUTION lung-thorax system compliance of 100 mL/cm H O, is participate in gas exchange. Thus, alveolar ventila- 2 sufficient to achieve a normal tidal volume of 500 mL/ tion is simply tidal volume minus dead space times breath. With normal spontaneous breathing, alveolar respiratory rate: pressure is below atmospheric (negative) during inspira- ˙ = × = © Jones & BartlettVA Learning,(VT – VDphys) LLC f (500 mL– 150 mL) © Jonestion and & aboveBartlett atmospheric Learning, (positive) LLC during expira- × 12 breath/min = 4200 mL/min or 4.2 L/min tion. Normal intrapleural pressures are slightly below NOT FOR SALE OR DISTRIBUTION NOTatmospheric FOR SALE at end OR expiration DISTRIBUTION and decrease (become A major purpose of ventilation is removal of CO . 2 more negative) during inspiration. These pressure Normal CO production (V˙ CO ) is about 200 mL/min 2 2 changes allow for inspiratory and expiratory gas flow. and the normal partial pressure of carbon dioxide in Figure 3-4 illustrates the changes in volume, alveolar the arterial blood (Paco ) is 40 mmHg. There is a direct 2 pressure (P ), intrapleural pressure (P ), and gas flow relationship between© alveolar Jones ventilation, & Bartlett CO Learning,produc- LLC alv © Jonespl & Bartlett Learning, LLC 2 during inspiration and expiration. tion, and arterial PacoNOT2: FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ˙ = × ˙ ÷ = × VA (0.863 VCO2) Paco2 (O.863 200) Negative Pressure Breathing ÷ 40 = 4.3 L/min (very close to 4.2 L/min above) ˙ Mechanical ventilation can either be invasive or non- Thus, as AV increases, Paco2 decreases and vice ˙ invasive, depending on the airway adjunct and needs versa.© Jones As VCO 2& increases Bartlett (e.g., Learning, increased metabolic LLC rate, © Jones & Bartlett Learning, LLC ˙ of the patient, and either positive or negative pressure. fever),NOT VA FOR must increase SALE ifOR Paco DISTRIBUTION2 is to remain constant. NOT FOR SALE OR DISTRIBUTION Today, almost all mechanical ventilation is provided Spontaneous Breathing by positive pressure. Beginning in the late 1920s, early examples of ventilatory support, however, were based At rest, the autonomic centers for respiratory control on the use of negative pressure (Clinical Focus 3-1). © Jones & withinBartlett the nucleusLearning, of the LLCtractus solitarius are active © JonesThe iron & Bartlettlung (Figure Learning, 3-1) was in LLChigh demand dur- and responsive to afferent feedback from chemore- ing polio outbreaks around the world. The principle of NOT FOR SALE OR DISTRIBUTION 5 NOT FOR SALE OR DISTRIBUTION ceptor and mechanoreceptor systems. The phases of operation was relatively simple: the patient was placed

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Alveolar Pr Alveolar –1 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION –5 essure O) Pr 2 –7

©(cm H Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC –9 Figure 3-5 The Biphasic Cuirass Ventilator.

Intrapleural NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Courtesy of United Hayek Industries Inc. 0.5 to provide negative pressure ventilation. The Biphasic Tidal Cuirass Ventilator (United Hayek) uses a plastic shell 0.25 © Jones & Bartlett Learning, LLC volume © Jones & Bartlett Learning, LLC Figure 3-5 (liters) coupled to a negative-pressure generator ( ). NOT FOR SALE OR DISTRIBUTION NOTHayek FOR Medical SALE uses OR the DISTRIBUTION term “biphasic” in its descrip- Volume Change Volume 0 tion of using both an active inspiratory (negative pressure) and expiratory (positive pressure) phase in its 0.5 operation.7 It has been used in a variety of patients with and without an endotracheal (ET) tube. The device also © Jones & Bartlett Learning, LLCfunctions as a bronchial hygiene© Jones device with & Bartlett capabilities Learning, LLC 0 NOT FOR SALE OR DISTRIBUTIONof high-frequency chest wall NOToscillation FOR and SALE generation OR DISTRIBUTION Air Flow (liters/sec) of a negative/positive pressure as a cough assist device.8 –0.5 Positive Pressure Breathing Time © Jones & Bartlett Learning, LLC Positive pressure© Jones ventilation & Bartlett rapidly gained Learning, in popular- LLC FigNOTure 3-4 FOR Single SALEBreath Analysis OR Curves.DISTRIBUTION Note that as the alveolar ity with improvementsNOT FOR in SALE design andOR function. DISTRIBUTION In the and intrapleural pressures decrease during inspiration, air flow and 1960s and 1970s, ventilators became much more so- volume increase achieving an inspiratory tidal volume of about 0.5 L. phisticated and required specially trained personnel to As these pressures return to their normal baseline, gas is exhaled. operate them safely and effectively Figure( 3-6). Expan- Creative Media Services, UT Health. sion of respiratory therapist educational programs co- © Jones & Bartlett Learning, LLC © Jonesincided & with Bartlett an upswing Learning, in the use LLC of positive pressure ventilators. These devices required a sealed airway via NOT FOR SALE OR DISTRIBUTION NOTa FOR cuffed SALE endotracheal OR DISTRIBUTION or tracheostomy tube (although on a stretcher within a metal tube with head exposed mask ventilation was possible). After advancing the en- to room air. A leather seal around the neck closed the dotracheal tube past the glottis (intubation) with its tip system, and a bellows attached to a mechanical pivot above the level of the carina, the cuff is inflated against like the drive mechanism© Jones of a locomotive & Bartlett alternately Learning, LLCthe wall of the trachea. The endotracheal© Jones & tube Bartlett is fixed Learning, LLC decreased the chamber pressure below atmospheric in position to provide reasonable assurance against it (inspiration) and thenNOT returned FOR the SALE chamber OR pressure DISTRIBUTION becoming dislodged and resuscitationNOT FOR bag ventilationSALE OR DISTRIBUTION to baseline (expiration). The transrespiratory system is maintained until ready to connect the patient to the pressures were transmitted to the airways and as airway positive pressure ventilator. pressure dropped below atmospheric, the patient in- The function of the ventilator is to provide a volume spired.© Jones Exhalation & Bartlett followed asLearning, the airway, intrapleural,LLC of gas to the© patient Jones with & suchBartlett sufficiency Learning, as to supply LLC 6 the alveoli and arterial system with oxygen and support andNOT transrespiratory FOR SALE system OR pressures DISTRIBUTION were reversed. NOT FOR SALE OR DISTRIBUTION The large space within the chambers did not prevent carbon dioxide removal. While various patient circuit spontaneous respiration, and it was possible to make configurations have been employed, in its most simpli- observations on the patient’s ventilatory progress. These fied form the ventilator is attached to the patient by two ventilators saved thousands of lives during the polio limbs of tubing joined at a “Y” connection. The inspira- © Jones & epidemics.Bartlett TheLearning, Emerson LLCiron lung was produced from© Jonestory limb & Bartlett carries gas Learning, from the ventilator LLC to the “Y” connector and endotracheal tube. The volume of air meant NOT FOR SALEthe 1930s OR into DISTRIBUTION the 1970s. The chest curaisse, body suit NOT FOR SALE OR DISTRIBUTION (Pulmowrap), and Portalung are other devices used for the lungs does not flow past the “Y” connector

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© Jones & Bartlett Learning, LLC © Jones & BartlettCLINICAL Learning, FOCUS 3-1 LLC Negative Pressure Ventilation NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Your patient is a 4-year-old boy diagnosed with spinal The plan was to reduce the backup rate as the muscle atrophy (SMA) since birth. He is chronically hy- patient’s spontaneous rate increased. Urine percarbic and a decision must be made concerning tra- output and renal function would be monitored.

cheostomy and mechanical ventilation. The parents are PETCO2 and O2 by pulse oximetry would be moni- adamantly opposed© toJones tracheostomy. & Bartlett The patient’s Learning, re- LLCtored continuously and ABGs© would Jones be drawn& Bartlett in Learning, LLC spiratory rate (f) isNOT 28 breaths/min, FOR SALE blood OR pressure DISTRIBUTION (BP) the morning and as needed (PRN).NOT TheFOR parents SALE OR DISTRIBUTION is 135/68, and heart rate (HR) is 105. He is diaphoretic seemed happy. and appears to be in distress. The most recent arterial blood gas (ABG) on room air (RA) is: Questions: ©pH Jones & Bartlett7.31 Learning, LLC 1. How would© youJones classify & eachBartlett of the Learning, three ABGs? LLC Was the chest cuirass successful in reversing the NOTPaco FOR2 SALE 65OR mmHg DISTRIBUTION 2. NOT FOR SALE OR DISTRIBUTION ventilatory failure? Pao2 55 mmHg − 3. Do you anticipate a continued decrease in the bicar- HCO3 32 mEq/L bonate level? Sao2 89% © Jones & BartlettA decision Learning, to institute LLC negative pressure ventila- © JonesAnswers: & Bartlett Learning, LLC NOT FOR SALEtion was OR agreed DISTRIBUTION upon. The Hayek chest cuirass was NOT1. FOR Blood SALE gas classification OR DISTRIBUTION used and set to –18 cm H2O to maintain a VT between Initial: Partially compensated respiratory acidosis 100 to 130 mL/breath (patient weight is 14 kg and the with moderate hypoxemia. estimated V desired was 8 mL/kg). The ventilator T A. Compensated respiratory acidosis with was set in a respiratory synchronization mode with © Jones & Bartlett Learning, LLCnormoxemia. © Jones & Bartlett Learning, LLC a backup rate of 18 breaths/min. Supplemental O 2 Within normal limits (WNL). was bled into the NOTsystem FOR at 4 L/min. SALE Within OR theDISTRIBUTION next B. NOT FOR SALE OR DISTRIBUTION 2 hours, the patient seemed more comfortable. An 2. Yes. − ABG drawn at 15 minutes post negative pressure 3. Possibly. If the Paco2 rises, the HCO3 may increase. − ventilation initiation is shown in (A) and at 2 hours in If the Paco2 does not change, the HCO3 may de- (B):© Jones & Bartlett Learning, LLC crease a bit© asJones the pH & moves Bartlett closer Learning, to 7.40. LLC NOTA pH FOR 7.37SALE OR DISTRIBUTIONB pH 7.43 NOT FOR SALE OR DISTRIBUTION

Paco2 53 mmHg Paco2 45 mmHg

Pao2 85 mmHg Pao2 89 mmHg − − HCO3 30 mEq/L HCO3 29 mEq/L

through the expiratory© limbJones as there & Bartlett is an expiratory Learning, LLCRespiratory clinicians adjust© variablesJones &including Bartlett flow, Learning, LLC valve that closes the exhalation limb during the inspira- volume, time, and pressure to provide optimal gas ex- tory phase. NOT FOR SALE OR DISTRIBUTIONchange while minimizing theNOT risk of FORbarotrauma. SALE Venti- OR DISTRIBUTION Once the inspiratory volume is delivered, the expira- lator adjustments can be complex and require advanced tory limb is opened to exhaust the volume of gas leaving training and experience. Untrained or inexperienced the lungs. The inspiratory tidal volume may be humidi- personnel should not make changes in mechanical ven- fied© andJones enriched & Bartlett with supplemental Learning, oxygen. LLC During tilation parameters,© Jones as serious& Bartlett patient Learning, safety concerns LLC inspiration,NOT FOR as gas SALE flows intoOR theDISTRIBUTION lung, the airway pres- may arise. InNOT any situationFOR SALE in which OR the DISTRIBUTION ventilator does sure will rise. The airway pressure is dependent on both not appear to be functioning correctly, immediately the machine’s set parameters and the compliance and disconnecting the patient from the ventilator and pro- resistance of the lungs being ventilated. Generally, the viding manual ventilatory support using a manual re- larger the tidal volume, the greater the peak pressure. suscitator bag is strongly encouraged. While the patient © Jones & Similarly,Bartlett the Learning, lower the lung LLC compliance, the greater the© Jonesis being & supported Bartlett using Learning, a manual LLC resuscitator bag with Figure 3-7 NOT FOR SALEpeak and OR plateau DISTRIBUTION pressure. illustrates a typi-NOTsupplemental FOR SALE oxygen, OR DISTRIBUTION the respiratory therapist can then cal ventilator patient circuit. troubleshoot the ventilator to identify the problem.

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Figure 3-6 Pressure and Volume Ventilators Introduced in the 1940s Through the Early 1970s. Top left, the Bird Mark 7 (introduced in 1958) and Bird Mark 8 (introduced in 1959). Top right, the Bennett TV-2P (introduced in 1948) and Bennett PR-2 (introduced in 1963). Bottom left, Bennett MA-1 volume ventilator (introduced in 1967) and Servo 900 (introduced in 1971). Bottom right, the Ohio 560 (introduced in the 1970s). Reproduced© Jones from Kacmarek & RM.Bartlett The Mechanical Learning, Ventilator: Past, present, LLC and future. Respir Care. Aug 2011;56(8):1170–1180;© Jones doi: 10.4187/respcare.01420 & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Figure 3-8 provides an example of ventilator graphics systems use a pressure monitoring line consisting of a depicting the pressure curves associated with positive length of noncompliant tubing that extends from the © Jones & pressureBartlett volume Learning, ventilation LLC with an end-expiratory © Jonesventilator & Bartlett to the proximal Learning, airway “Y”LLC connector. Most NOT FOR SALEpause. All OR pressures DISTRIBUTION reflect proximal airway pressure NOTmodern FOR SALE ventilators OR today DISTRIBUTION sense the pressure where (Paw), either measured directly or indirectly. Older expired gas returns to the ventilator via the expiratory

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© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC BOX 3-3 Factors that Increase Peak NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION INSP Inspiratory Pressure (PIP) Increased peak inspiratory flow EXP Humidifier Increased set tidal volume (VT) © Jones & Bartlett Learning, LLCIncreased airway resistance© Jones & Bartlett Learning, LLC Decreased total compliance Ventilator NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Monitoring line Increased PEEP Temperature ports Kinked or obstructed ET tube Fighting the ventilator Water trap © Jones & Bartlett Learning, LLC Coughing© Jones & Bartlett Learning, LLC FigureNOT 3-7 FOR An Example SALE of a MechanicalOR DISTRIBUTION Ventilator Patient Circuit. NOT FOR SALE OR DISTRIBUTION This circuit shows the inspiratory (green) and expiratory (gray) limbs that serve as a conduit of respirable gases between the ventilator (shown in gray) and the patient connection. A heated flow waveform, resistance of the ventilator circuit/ humidifier with attached water reservoir line is shown and heated endotracheal tube, and lung mechanics (compliance internal wires maintain ventilator circuit temperature and reduce and resistance). Proximal airway pressure may also in- © Jones & condensation.Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOTcrease FOR during SALE forced OR exhalation,DISTRIBUTION as noted with cough (Box 3-3). Maintaining PIP < 35 cm H2O should reduce the risk of pulmonary barotrauma.

PIP Plateau Pressure (P ) © Jones & Bartlett Learning, LLC plateau © Jones & Bartlett Learning, LLC Resistance In the VC mode, plateau pressure (Pplateau) is measured NOT FORflow SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION during an inspiratory hold maneuver, typically one Pplateau second or less in duration (see again Figure 3-8). At the end of inspiration, with Pplateau activated, the ventilator Compliance will continue to block the exhalation valve as the airway © Jones & Bartletttidal volume Learning, LLC pressure decreases© Jones from & a Bartlettpeak value Learning,(PIP) to the pla- LLC NOT FOR SALE OR DISTRIBUTION teau level. UnderNOT staticFOR conditions, SALE OR Pplateau DISTRIBUTION reflects alveolar pressure and the difference between PIP and P PEEP AutoPEEP plateau Total-PEEP reflects airway resistance (Raw), which can be easily calculated during VC ventilation:

PIP – Pplateau Raw = © Jones & FBartlettigure 3-8 AirwayLearning, Pressure During LLC Volume-Controlled Ventilation: © Jones & Bartlett Learning, LLCL NOT FOR SALEThe Pressure OR vs DISTRIBUTIONTime Scalar. Peak inspiratory pressure (PIP) is NOT FOR SALE ORInspiratory DISTRIBUTION flow( sec) the highest pressure reached during inspiration. An end inspiratory Pplateau is determined by elastic lung tissue recoil in breath hold allows for measurement of plateau pressure (Pplateau). The difference between PIP and Pplateau represents airway resistance the absence of airflow and allows for the calculation of (Raw). PEEP is positive end-expiratory pressure. Introduction of an end static total compliance (CST) during VC ventilation: expiratory pause allows for the measurement of autoPEEP. © Jones & Bartlett Learning, LLC © VJonesT & Bartlett Learning, LLC CST = NOT FOR SALE OR DISTRIBUTION Pplateau – baselineNOT FORpressure SALE OR DISTRIBUTION

limb of the circuit or within the internal ventilator circuit near the point where gas leaves the internal circuit Baseline Pressure and PEEP and enters the inspiratory limb of the external circuit. © Jones & Bartlett Learning, LLC The pressure© Joneswaveform & depicted Bartlett in FigureLearning, 3-8 drops LLC to a baseline or resting airway pressure during expiration. PeakNOT Inspiratory FOR SALE Pressure OR DISTRIBUTION If the baselineNOT pressure FOR is SALE the same OR as ambientDISTRIBUTION pressure, Thepeak inspiratory pressure (PIP) is the highest the baseline is recorded as zero. If the baseline pressure proximal airway pressure attained during the inspi- during the expiratory phase is above ambient pressure, ratory phase. During pressure-control ventilation, it is known as positive end-expiratory pressure (PEEP). © Jones & PIPBartlett is determined Learning, by the ventilatorLLC settings. During © JonesPEEP has& Bartlett been used Learning, since the early LLC days of positive volume-control (VC) pressure ventilation to maintain alveolar volumes dur- NOT FOR SALE OR DISTRIBUTION ventilation, PIP can be influenced NOT FOR SALE OR DISTRIBUTION by set tidal volume (VT), inspiratory flow, inspiratory ing expiration and to improve oxygenation. Initially,

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© Jones & Bartlett Learning, LLC © Jonesor intrinsic & Bartlett PEEP caused Learning, by air trapping LLC during the ex- NOTpiratory FOR SALE phase. This OR DISTRIBUTIONdynamic hyperinflation can lead to NOT FOR SALE OR DISTRIBUTION higher mean airway pressures and possible cardiovascular side effects (e.g., decreased venous return, decreased stroke volume, and decreased cardiac output). Patients with chronic obstructive pulmonary disease (COPD) © Jones & Bartlett Learning, LLCare especially likely to develop© autoPEEP Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Optimal PEEP As noted, the purpose of PEEP is to improve and maintain lung volumes and improve oxygenation in patients with acute restrictive pulmonary disease (e.g., pneumonia, © Jones & Bartlett Learning, LLC acute respiratory© Jones distress & syndrome Bartlett [ARDS], Learning, pulmonary LLC NOT FOR SALE OR DISTRIBUTION edema). A smallNOT amount FOR of SALE PEEP (3 OR to 5 DISTRIBUTIONcm H2O) has been suggested for most mechanically ventilated patients to prevent end-expiratory alveolar collapse; this is sometimes referred to as “physiologic PEEP.” High levels of extrinsic PEEP can increase the transmural wall pressures © Jones & Bartlett Learning, LLC © Jonesof the low-pressure& Bartlett great Learning, vessels (superior LLC and inferior NOT FOR SALE OR DISTRIBUTION NOTvena FOR cava) SALE and the OR right DISTRIBUTION and left ventricle. Compression Figure 3-9 The Water-Filled PEEP Column. of the vena cava can diminish venous return and ventricu- Courtesy Dr. Greg Holt. lar compression may affect diastolic filling. High levels of extrinsic PEEP combined with high levels of intrinsic PEEP was applied by simply submersing the distal end PEEP (air trapping or autoPEEP) may further reduce ve- of the expiratory limb© of Jones the ventilator & Bartlett circuit belowLearning, the LLCnous return. This assumes normal© Jones lung compliance & Bartlett as the Learning, LLC surface of a water container.NOT FOR Early SALEPEEP valve OR systems DISTRIBUTION transmural wall pressure effectsNOT are FORnot as easilySALE observed OR DISTRIBUTION were developed (Figure 3-9) and attached to the ven- through noncompliant lungs. tilator and filled with a volume of water. The weight of One approach to optimizing PEEP titrates the PEEP ˙ the water over the ventilator’s exhalation valve created level based on oxygen delivery (DO2). Recall that positive airway pressure during the expiratory phase oxygen delivery is simply cardiac output times arterial proportional© Jones to & the Bartlett height of Learning,the water column LLC in centi- oxygen content© Jones (D˙ O2 = & Q˙ TBartlett × Cao2). ToLearning, achieve the LLC meters.NOT A FORwater columnSALE 5OR cm inDISTRIBUTION height would result in optimal PEEPNOT level, FOR PEEP SALE is increased OR incrementallyDISTRIBUTION PEEP of 5 cm H2O. Today’s ventilators use much more followed by measurement of cardiac output or related sophisticated systems incorporating servo-adjusted so- parameters (blood pressure, mixed venous oxygen lenoid valves and pressure sensors to actively monitor levels). The optimal PEEP level is the level that op- and maintain airway pressures. PEEP set intentionally timizes D˙ O2. Other approaches to optimizing PEEP © Jones & toBartlett improve lungLearning, volumes LLCand oxygenation is known as © Joneslevels include& Bartlett compliance-titrated Learning, LLC PEEP and the use of NOT FOR SALEextrinsic OR PEEP DISTRIBUTION. NOTpressure–volume FOR SALE OR curves DISTRIBUTION to help set the PEEP level. PEEP studies can be performed by comparing AutoPEEP or Intrinsic PEEP increases in set (extrinsic) PEEP to cardiac output. Clinical Focus 3-2 provides an example of a PEEP Air trapping (aka dynamic hyperinflation) can occur study used to determine optimum PEEP. Caution with incomplete emptying of the lung during expira- © Jones & Bartlett Learning, LLCshould be exercised in using high© Jones levels of & PEEP Bartlett in Learning, LLC tion. Patients with obstructive lung disease are particu- the setting of hypotension, hypovolemia, increased larly prone to the developmentNOT FOR of airSALE trapping OR during DISTRIBUTION NOT FOR SALE OR DISTRIBUTION intracranial pressure (ICP), or pulmonary embolism.9 mechanical ventilation, especially if expiratory times are inadequate. Terms used for this air trapping dur- Mean Airway Pressure (Paw) ing positive pressure ventilation include autoPEEP, or intrinsic© Jones PEEP .& Bartlett Learning, LLC In addition ©to Jonesthe effect & ofBartlett PEEP on venousLearning, return, LLC NOTAutoPEEP FOR is notSALE observable OR DISTRIBUTION during positive pressure the respiratoryNOT care FOR clinician SALE should OR consider DISTRIBUTION other ventilation on the patient’s pressure-time curve without variables that affect mean airway pressure (Paw) dur- the use of an expiratory pause maneuver. Most modern ing mechanical ventilation with positive pressure. A ventilators allow for the introduction of an expiratory 2003 paper on mathematical modeling of mean airway pause to evaluate autoPEEP Turning once again to pressure used PEEP, I:E ratios, and Pplateau to make de- 10 © Jones & FigurBartlette 3-8, noteLearning, that as the LLC pressure curve proceeds to © Jonesterminations & Bartlett of mean Learning, airway pressures. LLC This article NOT FOR SALEthe right, OR the DISTRIBUTIONpressure increases during an expiratory NOTsuggests FOR SALE using a ORtarget DISTRIBUTION airway pressure to recruit alveoli hold maneuver. This increased pressure is the autoPEEP rather than using arterial blood gas analysis, PETCO2,

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© Jones & Bartlett Learning, LLC © Jones & BartlettCLINICAL Learning, FOCUS 3-2 LLC Optimal PEEP Study NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION An optimal PEEP study is requested for a patient on − HCO3 29 mEq/L mechanical ventilation with settings: Hg 10 g/dL Mode: PC-AC The patient’s ventilator indicates a delivered VT of Fio2: 100% © Jones & Bartlett Learning, LLC400 mL, and there are no spontaneous© Jones respirations. & Bartlett Learning, LLC PIP: 28 cm H2O NOT FOR SALE OR DISTRIBUTIONThe patient has increasing patchyNOT infiltrates FOR SALE on chest OR DISTRIBUTION RR: 16 bpm x-ray. A PEEP study has been ordered, and you have developed the following table. All measures were PEEP: +12 cm H2O made at an Fio of 100% with a Hb of 10 g/100 mL Recent ABG results: 2 blood. The results displayed were obtained after pH 7.30 © Jones & Bartlett Learning, LLC 10 minutes at© eachJones PEEP & level. Bartlett Learning, LLC NOTPaco FOR2 60 mmHg SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Pao2 45 mmHg

PEEP Sao2 BP CO D˙ O2 PCWP CST C(a-v)O2

16 82 100/58 6.2 700 16 36 4.1

18 92 105/68 6.0 768 16 48 5.6 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 20 100 95/55 5.8 806 17 37 6.3 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 22 100 80/52 5.3 736 20 33 6.0

24 100 65/40 5.1 714 23 23 4.4

Questions:© Jones & Bartlett Learning, LLC the next ©PEEP Jones level (20 & cmBartlett H2O), blood Learning, pressure, LLC 1.NOT How FORwould SALEyou interpret OR DISTRIBUTIONthe patient’s initial cardiac output,NOT FORand compliance SALE OR decrease DISTRIBUTION and (recent) ABG? C(a-v)O2 increases. 2. What level of PEEP could be considered optimal? 3. Many variables can be used to help determine optimal PEEP. They include hemodynamic mea- 3. What are other variables that can be used to de- © Jones & Bartlettvelop anLearning, optimal PEEP LLC study? © Jonessures, & Bartlettlung mechanics, Learning, and indices LLC of oxygenation – – and ventilation (e.g., BP, CO, CI, D˙ O2, PvO2, SvO2, NOT FOR SALEAnswers: OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION C(a-vO2), Pao2, Sao2, P(A-a), Pao2/Fio2, CST, The recent blood gas shows a partially compen- 1. Paco2 – PETCO2, and shunt fraction [Q˙ S/Q˙ T]). sated respiratory acidosis with moderate to severe ABG, arterial blood gas; BP, blood pressure; CO, cardiac output; hypoxemia. CST, static compliance; PC-AC, pressure control-assist control; PCWP, pulmonary capillary wedge pressure; PEEP, positive 2. At PEEP of 18 cm© H Jones2O the BP, & Sao Bartlett2, CO, and Learning, D˙ O2, LLC © Jones & Bartlett Learning, LLC and C O are acceptable and C is at its highest end-expiratory pressure; PIP, peak inspiratory pressure; RR, (a-v) 2 NOT FOR SALEST OR DISTRIBUTIONrespiratory rate. NOT FOR SALE OR DISTRIBUTION value (48) suggesting that this represents the best

or optimal PEEP level. Although D˙ O2 is highest at

and oximetry alone for ventilator adjustments. The in- direct, and a 1 cm H2O PEEP increase causes a 1 cm creased focus on the balance of I:E ratios and PEEP with H2O rise in Paw. Factors that increase TI will increase particular attention to inspiratory time (TI) to manage Paw. Changes in pulmonary mechanics (e.g., low lung 10 © Jones & PawBartlett over PEEP Learning, settings wasLLC the intent of the paper. A© Jonescompliance & Bartlett and high Learning, airflow resistance) LLC also may con- = NOT FOR SALEless stringent OR DISTRIBUTION method forwards the equation Paw ½ NOTtribute FOR toSALE an increased OR DISTRIBUTION Paw. Variables that can influence (PIP – PEEP) × (TI / Ttot) + PEEP. The effect of PEEP is mean airway pressure are described in Box 3-4.

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© Jones & Bartlett Learning, LLC © Jones & BartlettBOX 3-4 Learning, Factors That LLC May Increase Mean BOX 3-5 Bilevel Positive Airway Pressure NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Airway Pressure (Paw) (BiPAP) for OSA Increased inspiratory time BiPAP can be expressed as a combination of IPAP Increased I:E ratio over EPAP. Decreased expiratory© Jones time & Bartlett Learning, LLCIPAP can reach 30 cm H2©O. Jones & Bartlett Learning, LLC Increased tidal NOTvolume FOR SALE OR DISTRIBUTIONEPAP is usually 4 to 8 cmNOT H2O belowFOR IPAP. SALE OR DISTRIBUTION Increased extrinsic PEEP EPAP is set to abolish obstructive apneas. AutoPEEP IPAP is set to improve the inspiratory flow wave Decreased spontaneous breathing characteristics and abolish hypopneas and snoring. ©Down-ramp Jones & (decreasing)Bartlett Learning, inspiratory flowLLC © Jones & Bartlett Learning, LLC NOTpattern FOR SALE OR DISTRIBUTION IPAP: inspiratoryNOT positive FOR airway SALE pressure; OR EPAP: DISTRIBUTION expiratory positive airway pressure. Low lung compliance High airway resistance (Raw)

© Jones & Bartlett Learning, LLC © Jonesacute exacerbations& Bartlett Learning,of COPD. Extubation LLC to NIV has NOT FOR SALE OR DISTRIBUTION NOTalso FOR been SALE recommended OR DISTRIBUTION for certain patients at risk Invasive vs. Noninvasive Ventilation of extubation failure. NIV is also sometimes used in patients with chronic neuromuscular disease. NIV for Before comparing the similarities and differences be- the treatment of obstructive sleep apnea will be briefly tween invasive and noninvasive ventilation, we should discussed below. revisit the goal of mechanical ventilation: to support NIV has seen great strides in technology and mask oxygenation and CO© removal. Jones Mechanical & Bartlett ventila- Learning, LLC © Jones & Bartlett Learning, LLC 2 interface devices in the treatment of obstructive sleep tion requires a triggerNOT (breath FOR initiation), SALE a ORlimit DISTRIBUTION(size NOT FOR SALE OR DISTRIBUTION apnea (OSA) since the mid-1990s. Companies such as of the breath), and a cycle (transition of inspiration to ResMed, Respironics, and Fisher-Paykel have invested expiration). The forms the trigger, limit, and cycle vari- resources into research and development of better ables take are dependent on the device, the patient’s patient-sensing capabilities, improved mask comfort condition, and the level of expertise of the respiratory and fit, and new modes of NIV. For example, Respiron- care clinician.© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ics developed an expiratory pressure release technol- NOTSimilarities FOR between SALE invasive OR DISTRIBUTION and noninvasive ven- NOT FOR SALE OR DISTRIBUTION ogy (CFLEX) adjustable from 0 to 3, with 3 providing tilation (NIV) include positive pressure breath delivery the greatest drop in exhaled pressure. CFLEX may and the ventilator’s airway pressure and flow sensing ca- improve patient comfort and compliance. ResMed fol- pabilities. Many new noninvasive devices can measure lowed closely with EPR (expiratory pressure release) volume directly. Size and cost of ventilators designed that has an adjustable, set pressure drop at the start of © Jones & forBartlett invasive Learning,vs noninvasive LLC use are major differences © Jones & Bartlett Learning, LLC exhalation. between the two. For example, simple NIV devices for NOT FOR SALE OR DISTRIBUTION NOT FORThe SALErelief of ORpatient DISTRIBUTION anxiety associated with the the treatment of obstructive sleep apnea (OSA) may higher pressures sometimes necessary to control cost as little as $600 and fit on a nightstand, while a OSA was the driving force behind CFLEX and EPR sophisticated critical care ventilator may cost $35,000 development. If higher pressures (e.g., > 12 cm or more and require significant space at the bedside. © Jones & Bartlett Learning, LLCH2O) were used in OSA therapy,© Jones patients & often Bartlett com- Learning, LLC NIV requires a spontaneously breathing patient with an plained of difficulty exhaling against the pressure. adequate respiratoryNOT drive, FORwhile a SALE critical careOR ventila-DISTRIBUTIONBilevel positive airway pressureNOT (BiPAP) FOR would SALE be OR DISTRIBUTION tor can ventilate apneic patients with acute or chronic sometimes instituted (Box 3-5), but this added to the respiratory failure. Another difference between NIV and cost of the device. A variation on BiPAP was developed, invasive ventilation is the interface between the patient the spontaneous-timed (S/T) mode. With BiPAP S/T and the ventilator. Both methods require a sealed airway (trademark Respironics), inspiratory and expiratory to deliver© Jones positive & Bartlett pressure, butLearning, invasive ventilation LLC re- © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION pressures wereNOT set along FOR withSALE a backup OR DISTRIBUTION rate. If the de- quires an endotracheal or tracheostomy tube be placed vice measured zero inspiratory flow for a set period, with the cuff inflated. the inspiratory positive airway pressure (IPAP) breath would be delivered (i.e., time triggered to inspiration). Noninvasive Ventilation BiPAP S/T could provide support for some cases of © Jones & NIVBartlett can be Learning,used to provide LLC ventilatory support to © Jonescomplex & sleepBartlett apnea Learning, (defined as atLLC least 50% of all respi- NOT FOR SALEpatients OR with DISTRIBUTIONa wide variety of conditions, which may NOTratory FOR events SALE being OR central DISTRIBUTION in origin); however, the IPAP be acute or chronic. For example, in the acute care breath could fall short of preventing sleep arousal as setting, NIV is often used to support patients with seen via EEG and O2 desaturation. If the IPAP pressures

9781284139860_CH03_095_154.indd 106 21/02/19 5:37 PM Ventilation 107

© Jones &were Bartlett increased Learning, to cover the LLC reduced machine delivered© Jonestitration & studyBartlett is a guess. Learning, If the pressure LLC range is left at tidal volume, the patient could arouse and awaken to NOTits FOR initial SALE setting, OR 4 to 20DISTRIBUTION cmH2O, the patient (especially NOT FOR SALEsome very OR high DISTRIBUTION pressures. a very tall patient) may inspire with a greater flow than The next generation of NIV to treat central delivered and a feeling of air hunger may result. If the sleep apnea and forms of complex sleep apnea was patient on the same settings with OSA is asleep, the automatic-servo ventilation (auto-SV, trademark Respi- autoPAP will respond to his or her apnea by detection ronics) and later adaptive-servo© Jones ventilation& Bartlett (trademark Learning, LLCand will increase pressure provided.© Jones Over & time, Bartlett the pa- Learning, LLC ResMed). Auto-SV wasNOT considered FOR SALE a respiratory OR DISTRIBUTION assist tient will either get to the pointNOT where FOR the attained SALE pres OR- DISTRIBUTION device, similar to BiPAP S/T with pressure support. sure allows for ventilation or the patient may arouse and Auto-SV would “view” the patient’s rate and volume roll to his or her side, where the device lowers the pres- when the device was initiated (patient awake) and sure to a new baseline. Put another way, sleep-disordered mimic that pattern during the night. If the tidal vol- breathing is required to reach the appropriate thera- umes© fellJones short, & pressure Bartlett support Learning, would be LLCadded to peutic pressure.© Jones The patient & Bartlett may also Learning,awaken and feel LLC Figure 3-10 increaseNOT volume FOR (SALE OR) DISTRIBUTIONThe auto-SV would in- that the deviceNOT is not FOR working SALE at all. OR This DISTRIBUTION could result in crease pressures to cover obstructive respiratory events reduced compliance. Ideally, the clinician should know with an adjustable range of pressures; the rate could the appropriate pressures for each patient that treat OSA be set or left in an auto-detection mode and the level while supine, on the patient’s side, and in REM sleep. of pressure support could be set as a fixed number or The autoPAP device could then be set with a minimum © Jones & rangeBartlett for auto-adjust. Learning, These LLC added features, however, © Jonespressure & treatingBartlett OSA Learning, while on the LLC patient’s side with NOT FOR SALEresult in OR a cost DISTRIBUTION approximately 5 times the cost of a basicNOT the FOR idea SALEthat the ORpressures DISTRIBUTION may not be too far from CPAP device. controlling OSA while in supine REM sleep. Minimally, Automatic positive airway pressure or autoPAP is a the clinician should follow any patient on autoPAP with device that continues to be ordered for OSA treatment. overnight oximetry to assess therapeutic effectiveness. The pressure range for autoPAP is adjustable from 4 to Suggested indications for autoPAP are noted in Box 3-6. 20 cm H2O. By algorithm,© Jones the device & Bartlett can detect Learning, a re- LLC © Jones & Bartlett Learning, LLC duced or absent inspiratoryNOT FOR flow andSALE stepwise OR increase DISTRIBUTION NOT FOR SALE OR DISTRIBUTION the delivered pressure. There are problems, however, Invasive Ventilation associated with autoPAP. Primary among them is the in- Invasive positive pressure ventilation opens a wide ability to detect central versus obstructive sleep apnea. array of ventilatory capabilities using sophisticated Some units will not increase pressure over 10 cm H2O critical care ventilators. The goals remain the same, unless© Jones there is a& secondary Bartlett indication Learning, of obstructive LLC including assuring© Jones oxygenation & Bartlett needs Learning, are met and sup-LLC respiratoryNOT FOR events, SALE such as OR the DISTRIBUTIONacoustical vibration of porting ventilationNOT FOR until theSALE patient OR can DISTRIBUTION return to his snoring. A known problem of positive pressure therapy or her baseline ventilatory status. Modern critical care noted during a CPAP titration study for OSA is the po- ventilators have sophisticated alarms and monitor- tential for central apnea generation at higher pressures. ing systems, advanced graphic displays, and a wide A second problem and more likely occurrence is a sub- array of modes available ranging from conventional © Jones & therapeuticBartlett Learning,pressure range LLC set on autoPAP. Picking the © Jonesvolume-control & Bartlett continuous Learning, mandatory LLC ventilation autoPAP pressure range without the benefit of a CPAP NOT FOR SALE OR DISTRIBUTION NOT(VC-CMV) FOR SALE to pressure-control OR DISTRIBUTION continuous mandatory

Crescendo Decrescendo Flow BOX 3-6 Indications for Automatic Positive Airway Pressure (autoPAP)

© Jones & BartlettCentral Learning, LLC1. Initial therapy to treat OS©A Jones prior to CPAP& Bartlett Learning, LLC NOT FOR SALEapnea OR DISTRIBUTIONtitration NOT FOR SALE OR DISTRIBUTION Pressure 2. AutoPAP trial after significant weight change to assist adjust CPAP pressure 17 IPAPmax 3. Patient c/o aerophagia (air swallowing) while on © Jones & Bartlett Learning, LLC CPAP © Jones & Bartlett Learning, LLC 9 IPAP NOT FOR SALE OR DISTRIBUTION min As primaryNOT ther FORapy ifSALE optimal OR pressures DISTRIBUTION are EPAP 7 4. Decrease in Increase in Backup known: side, supine, REM cm H2O pressure pressure rate support support 5. As primary therapy in patients with mild OSA and low BMI Figure 3-10 Automatic-Servo Ventilation. Pressure support is © Jones & Bartlett Learning, LLC © JonesBMI, body& Bartlett mass index; Learning,CPAP, continuous LLC positive airway pres- automatically adjusted to minimize fluctuations in V and prevent NOT FOR SALE OR DISTRIBUTION T NOT FORsure; OSA, SALE obstructive OR sleep DISTRIBUTION apnea; REM, rapid eye movement airway obstruction. If central apneas arise, the backup rate will sleep deliver IPAP-associated breaths.

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© Jones &ventil Bartlettation (PC-CMV),Learning, to LLC inverse ratio ventilation, to © Jonesthis chapter. & Bartlett The ventilation Learning, of the LLC patient with acute various permutations of intermittent mandatory ven- NOTrespiratory FOR SALE failure OR superimposed DISTRIBUTION on chronic respiratory NOT FOR SALEtilation (IMV),OR DISTRIBUTION to various volume targeting schemes failure is described in Clinical Focus 3-3. (e.g., pressure-regulated volume control [PRVC], Ventilator Initiation volume support [VS], and adaptive pressure control [APC]). Modern critical care ventilators also Indications for mechanical ventilation and ventilator ini- often have many adjunct© Jones features & and Bartlett modes in- Learning, LLCtiation are described in Chapters© Jones 5 and 6. & Once Bartlett the deci Learning,- LLC automatic tube compensation (ATC) cluding NOT FOR SALE OR, DISTRIBUTIONsion to provide ventilatory supportNOT isFOR made, SALE mechanical OR DISTRIBUTION airway pressure release ventilation (APRV), propor- ventilation is initiated within specific parameters. Typi- tional assist ventilation (PAV), or adaptive support cally, orders will be given for mode, Fio2, VT (or PIP), ventilation (ASV), as well as the capability to provide respiratory rate, PEEP, and pressure support. Some in- NIV. Many of these modes will be introduced later in stitutions allow for ventilator initiation and adjustments © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC CLINICALNOT FOR FOCUS SALE 3-3 OR Acute DISTRIBUTION Ventilatory Failure SuperimposedNOT FOR on Chronic SALE ORVentilatory DISTRIBUTION Failure

Mrs. Ortiz is a 78-year-old female with a 110 pack- (A) (B) (C) (D) year history of smoking. She has been diagnosed with © Jones & Bartlett Learning, LLC © Jones & BartlettInitial 1 Week Learning, Respiratory LLC Mechanical COPD and her “normal” arterial blood gas consists ABG of Illness Failure Ventilation NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION of pH 7.36, Paco2 55 mmHg, and Pao2 60 mmHg on pH 7.36 7.39 7.29 7.62 − room air. Her HCO3 is calculated to be 30 mEq/L. Paco2 55 68 86 40 She develops pneumonia and presents to the emer- Pao2 60 50 45 60 − gency department in respiratory distress. Her ABG HCO3 30 40 40 40

results in the ED are:© Jones pH 7.21, Pa& coBartlett2 70 mmHg, Learning, and LLCQuestions: © Jones & Bartlett Learning, LLC Pao 45 mmHg, with HCO − 34 mEq/L. Her condi- 2 NOT FOR3 SALE OR DISTRIBUTION1. Review the ABGs and determineNOT theirFOR classifica- SALE OR DISTRIBUTION tion worsens, and she is intubated and placed on tions for A, B, C, and D. mechanical ventilation. Her ventilation is supported 2. When mechanical ventilation is instituted and the to maintain arterial blood gases similar to her base- Paco is “normal” at 40 mmHg, what is causing the line: compensated respiratory acidosis with mild 2 apparent metabolic alkalosis? hypoxemia.© Jones Intravenous& Bartlett antibiotics Learning, are LLCadministered © Jones & Bartlett Learning, LLC Would it have been more appropriate to ventilate untilNOT resolution FOR SALE of the ORpneumonia. DISTRIBUTION Mrs. Ortiz is 3. NOT FOR SALE OR DISTRIBUTION this patient to her baseline Paco of 55 mmHg? weaned from mechanical ventilation, extubated, and 2 discharged. Answers: To summarize, Mrs. Ortiz’s “normal” baseline can 1. A. Compensated respiratory acidosis with mild © Jones & Bartlettbe described Learning, as chronic LLC ventilatory failure (com- © Joneshypoxemia & Bartlett (chronic Learning, ventilatory failure);LLC B. Compen- NOT FOR SALEpensated OR respiratory DISTRIBUTION acidosis) and mild hypoxemia. NOT FORsated SALErespiratory OR acidosis DISTRIBUTION with moderate hypoxemia Following acute exacerbation of his COPD, she de- (chronic ventilatory failure); C. Partially compen- veloped acute on chronic ventilatory failure with a sated respiratory acidosis with moderate hypoxemia partially compensated respiratory acidosis and severe (acute ventilatory failure superimposed on chronic hypoxemia. Following treatment, resolution of her ventilatory failure); D. While this looks like an un- pneumonia and ventilator© Jones discontinuance, & Bartlett sheLearning, has LLCcompensated metabolic alkalosis© Jones with mild& Bartlett hypox- Learning, LLC returned to her baselineNOT statusFOR ofSALE chronic OR ventilatory DISTRIBUTION emia, it is a relative hyperventilationNOT FOR with SALE respect ORto DISTRIBUTION

failure. the patient’s baseline Paco2 of 55, resulting in alka- Mrs. Ortiz might have taken another path if the losis. The ventilatory settings should be adjusted. development of worsening respiratory failure had 2. This patient’s “normal” baseline Paco2 is 55 mm Hg progressed© Jones more & Bartlett slowly allowing Learning, for further LLC renal resulting ©in aJones pH of 7.36 & (seeBartlett initial ABGLearning, - A). If the LLC compensation of a worsening Paco . In this second NOT FOR SALE OR DISTRIBUTION2 initial ventilatorNOT FORsettings SALE result inOR a Pa DISTRIBUTIONco2 of 40, example, the original ABG is followed by worsening the pH will increase as noted (see ABG Mechanical ventilatory status with renal compensation, then re- Ventilation - D). The ventilator settings have created spiratory failure, and finally, mechanical ventilation is a relative hyperventilation with respect to the pa- initiated with overventilation. tient’s baseline Paco of 55 resulting in an alkalosis. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning,2 LLC Yes. The targeted Paco should have been the pa- NOT FOR SALE OR DISTRIBUTION NOT3. FOR SALE OR DISTRIBUTION2 tient’s “normal” baseline (i.e., Paco2 = 55).

9781284139860_CH03_095_154.indd 108 21/02/19 5:37 PM Ventilator Principles 109

© Jones &per Bartlett protocol. Learning, Initial ventilator LLC settings are keyed into the© Jonescompressed & Bartlett gas source. Learning, These older LLC pneumatically ventilator’s control interface. The respiratory therapist NOTpowered FOR SALE ventilators OR (e.g., DISTRIBUTION Bird Mark 7, Bennett PR-2) in- NOT FOR SALEtypically OR chooses DISTRIBUTION the patient-trigger method, trigger ef- corporated needle valves, flexible diaphragms, ceramic fort, inspiratory time or flow, and flow waveform (VC valves, pneumatic bleed-down cartridges, flow-sensitive modes), and adjusts settings to ensure patient–ventila- valves, and Venturi devices to perform the various tor synchrony and effective ventilation. Alarm settings functions required to ventilate patients. These devices are entered, and patient© Jones response & as assessed. Bartlett Learning, LLCcould be powered by 100% oxygen,© Jones which & could Bartlett be di- Learning, LLC Assessment to ensureNOT successful FOR SALE achievement OR DISTRIBUTION of luted using an on/off ventureNOT device FOR to provide SALE 100% OR DISTRIBUTION ventilatory support goals begins immediately. This will O2 or a moderate concentration oxygen (40% to 60%). include patient appearance, breath sounds, and assess- These ventilators also could be powered by compressed ment of ventilator volumes, pressures, and flows. As- air to provide 21% oxygen or blended gas to provide a sessment of oxygenation (Spo2), ventilation (respiratory precise FIO2. ˙ rate,© V JonesT, VE, arterial & Bartlett blood gases, Learning, and end-tidal LLC CO2), Modern ©pneumatically Jones & poweredBartlett ventilators Learning, require LLC andNOT cardiovascular FOR SALE status OR(HR, DISTRIBUTION BP, ECG) should follow. two 50-psi compressedNOT FOR gas SALE sources OR (air DISTRIBUTIONand oxygen) and Clinicians should be reminded that when mechanical incorporate microprocessor-controlled valves to pro- ventilation does not appear to be functioning prop- vide the desired oxygen concentration and gas flows to erly, the ventilator should be disconnected, and bag the patient. These are known as pneumatically powered ventilation resumed until proper ventilator operation microprocessor-controlled ventilators. © Jones & andBartlett airway patencyLearning, can be LLC confirmed. Initial problems© Jones & Bartlett Learning, LLC NOT FOR SALEsometimes OR encountered DISTRIBUTION when the patient is placed on NOTElectrically FOR SALE Powered OR DISTRIBUTION Ventilators the ventilator may be due to pain and anxiety, inade- The first truly sophisticated modern critical care ven- quate oxygenation or ventilation, cardiac/cardiovascular tilators were electrically powered and controlled and problems, or improper ventilator settings. Solutions incorporated internal air compressors, blowers, bellows, may be as simple as altering the ventilator settings, se- or pistons to deliver gas to the patient. These ventilators dation (anxiety) and analgesia (pain), or suctioning to © Jones & Bartlett Learning, LLCwere introduced in the 1960s© and Jones 1970s and& Bartlett allowed for Learning, LLC remove secretions from the airway. Airway problems NOT FOR SALE OR DISTRIBUTIONprecise control of Fio , deliveredNOT tidal FOR volume, SALE respira- OR DISTRIBUTION include secretions, obstruction, or bronchospasm, all 2 tory rate, and inspiratory flow or time. PEEP was an of which may cause triggering of high-pressure alarms integrated feature and the ventilators could be used to in the VC mode and decreased V in the PC mode. For T provide patient- or time-triggered ventilation (assist- example, the endotracheal tube may be out of position, control or A/C). By the 1970s, intermittent mandatory kinked, or partially occluded. Breath sound assess- © Jones & Bartlett Learning, LLC ventilation (IMV)© Jones and synchronized & Bartlett intermittentLearning, man- LLC ment and attempting to pass a suction catheter can NOT FOR SALE OR DISTRIBUTION datory ventilationNOT FOR(SIMV) SALE became OR common DISTRIBUTION options. sometimes identify the cause. Other serious problems Classic electrically powered ventilators included the include pneumothorax, pulmonary edema, pulmonary MA-1, Ohio 560, Emerson 3PV and IMV Emerson, embolus, or cardiovascular compromise. Once the pa- and Bear series (e.g., Bear-1, Bear-2, Bear-3). These tient is stable, comfortable, and adequately oxygenated ventilators could be described as single circuit, in and ventilated, a regular program of assessment, moni- © Jones & Bartlett Learning, LLC © Joneswhich &the Bartlett gas power Learning, source was sent LLC directly to the pa- toring, and care is instituted. NOT FOR SALE OR DISTRIBUTION NOTtient, FOR or SALE double circuit,OR DISTRIBUTION in which the gas power source was directed to a bellows housed within a canister. Ventilator Principles Single-circuit devices included the rotary piston, IMV Emerson, and the Bear series. Double-circuit systems, Input Power and Control Systems such as the MA-1 and Ohio 560, used a blower or com- Mechanical ventilators© Jonesmust incorporate & Bartlett a power Learning, LLCpressor to push a bellows containing© Jones mixed & gasBartlett upward; Learning, LLC source to perform theNOT work FOR required, SALE known OR as theDISTRIBUTION in- the gas within the bellows wouldNOT then FOR be delivered SALE toOR DISTRIBUTION put power. Power sources may be pneumatic or electric. the patient (blower-bellows system). These ventilators Pneumatically powered ventilators connect to an exter- were extremely efficient, safe, and reliable and allowed nal high-pressure gas source, while electrically powered for the development of the sophisticated approach to ventilators use electricity to power internal compres- critical care and support of the patient in respiratory sors,© blowers,Jones pistons,& Bartlett or bellows. Learning, Ventilator LLC control failure that ©we Jones see today. & Bartlett Learning, LLC systemsNOT use FOR pneumatic SALE valves, OR DISTRIBUTIONelectrical circuits, or mi- NOT FOR SALE OR DISTRIBUTION croprocessor controls to regulate oxygen concentrations Control Systems and gas flow to the patient. Most modern critical care ventilators today are microprocessor controlled and require a 120-volt continuous Pneumatically Powered Ventilators © Jones & Bartlett Learning, LLC © Joneselectrical & Bartlett supply with Learning, stepped-down LLC resistors reducing NOT FOR SALEPneumatically OR DISTRIBUTION powered ventilators require a com- NOTvoltage FOR toSALE control OR various DISTRIBUTION onboard ventilator systems. pressed gas source, either air or oxygen or both. Older Most ventilators possess a battery backup designed to pneumatic ventilators were powered using only one continue ventilation until a substitute power supply

9781284139860_CH03_095_154.indd 109 21/02/19 5:37 PM 110 CHAPTER 3 Principles of Mechanical Ventilation

© Jones &is Bartlett provided (generatorLearning, backup). LLC Some deep-cycle gel © JonesControl & Bartlett systems mayLearning, be open loopLLC or closed loop. batteries can last 10 hours, but many systems are not NOTAn FOR open-loop SALE system OR doesDISTRIBUTION not incorporate a feedback NOT FOR SALEdesigned OR to support DISTRIBUTION ventilation for more than 2 hours. signal to assure a specific ventilator parameter has There have been reported cases of ventilator failure been met. For example, a ventilator in which a micro- due to batteries beyond their useful life not accepting processor control system is used to set a specific tidal a charge and faulty battery level indicators. If backup volume may have no feedback system to adjust gas flow electrical power systems© Jones do not respond& Bartlett immediately, Learning, LLCin the presence of a change in© actual Jones delivered & Bartlett tidal. A Learning, LLC the clinician should resumeNOT FOR bag ventilation SALE OR using DISTRIBUTION a closed-loop system uses a microprocessor-controlledNOT FOR SALE OR DISTRIBUTION manual resuscitator bag. Most modern critical care feedback system to adjust gas flow based on measured ventilators also require high-pressure gas sources, both values. For example, with a closed-loop system the op- oxygen and compressed air in most cases. Like backup erator may set a specific tidal volume. The ventilator electrical supply, some mechanical ventilators possess then compares the actual delivered volume to the set onboard© Jones gas compressors & Bartlett capable Learning, of driving LLC ventilator value and adjusts© Jones gas delivery & Bartlett based on Learning, the compari LLC- functions.NOT FOR The usualSALE case OR is connecting DISTRIBUTION both oxygen son. AdaptiveNOT targeting FOR for SALE tidal volume OR DISTRIBUTION using pres- and air to 50-psi sources. Piped in medical gas supply sure support or pressure control provides an example systems are built into the walls of hospitals with mul- of a closed-loop control system known as adaptive tiple air and oxygen outlets in each modern ICU room. pressure control (APC). APC is available as pressure- Large, liquid oxygen systems and powerful medical gas regulated volume control (PRVC, Getinge Servo-i), auto © Jones & airBartlett compressors Learning, provide theLLC sources for compressed air© Jonesflow (Dräger & Bartlett Evita Infinity Learning, v500), adaptive-pressureLLC NOT FOR SALEand oxygen. OR DISTRIBUTION NOTventil FORation SALE (APV, OR Hamilton DISTRIBUTION G5), and volume control Ventilators incorporate pressure regulation devices plus (VC+, Puritan Bennett). and solenoid controllers to provide the desired air/O2 Most ventilators incorporate a control panel or a mix to deliver the desired Fio2 and gas flow to the pa- user interface, which may include mechanical or virtual tient. These pressure/flow regulation devices may incor- knobs, buttons, and switches to adjust various ventila- porate a pneumatic diaphragm,© Jones electromagnetic& Bartlett Learning, valve, LLCtor parameters. Adjustments© may Jones include & mode, Bartlett Fio2, Learning, LLC poppet/plunger valve,NOT or microprocessor- FOR SALEcontr ORolled DISTRIBUTION VT or pressure control level, respiratoryNOT FOR rate, SALE inspira- OR DISTRIBUTION proportional solenoid valves.4 The control system of a tory flow or inspiratory time, PEEP, pressure support, mechanical ventilator generally uses a combination of ventilator alarms, and ventilator graphic displays. pressure and electrical/microprocessor-controlled sys- Figure 3-11 provides an example of a modern critical tems to shape and deliver the breath. care ventilator’s user interface. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC

NOT FOR 0.700SALE OR DISTRIBUTIONPaw-V 50 V-FlowNOT FOR Pmean SALE ORPEEP DISTRIBUTION

0.500 25 10 5 0 0.300 Vol. % Flo2 –25 0.100 © Jones & Bartlett Learning,0 LLC –50 © Jones & Bartlett Learning,35 LLC –10 0020 40 cm H O 0.200 0.4000.600 L NOT FOR SALE OR DISTRIBUTION 2 NOT FOR SALE OR DISTRIBUTIONL/min MV 50 Flow L/min 25 4.5

0 L/min MVspn –25© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC –50NOT FOR SALE OR DISTRIBUTION NOT0 FOR SALE OR DISTRIBUTION bpm F 0.700 total Volume L 0.500 10 0.300 L V © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning,Ti LLC 0.100 NOT FOR SALE0 OR DISTRIBUTION NOT FOR SALE0.450 OR DISTRIBUTION 0246810121416Sec

35 .450 1.7 10 5 0

O2 VT Tinsp f PEEP Psupp © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Figure 3-11 Example of a Ventilator User Interface with Alphanumeric, Waveform, and Loop Displays. NOT FOR SALEReproduced withOR permission DISTRIBUTION from Chatburn RL. Fundamentals of Mechanical Ventilation. Cleveland,NOT OH: FOR Mandu Press SALE Ltd. 2003 OR DISTRIBUTION

9781284139860_CH03_095_154.indd 110 21/02/19 5:37 PM Ventilator Principles 111

Figure 3-12 The ParaPAC Pneumatically Powered Transport Ventilator. Courtesy of Smiths Medical. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC FewNOT critical FOR care SALE ventilators OR DISTRIBUTIONuse purely pneumatic NOT FOR SALE OR DISTRIBUTION controls, but they do play a role in ventilators used for patient transport and in the hyperbaric environment. For example, the ParaPAC Ventilator (Figure 3-12) is a pneumatically powered and controlled, time and © Jones & manualBartlett triggered, Learning, flow and LLC pressure limited, and © Jones & Bartlett Learning, LLC NOT FOR SALEtime-cycled OR ventilatorDISTRIBUTION with spontaneous breathing ca- NOT FOR SALE OR DISTRIBUTION pability.11 This ventilator is well-suited as a transport ventilator since it does not require an external electrical power source or battery. It can be made magnetic Figure 3-13 The Zoll 731 EMV+ Transport Ventilator. resonance imaging (MRI) compatible, but has shown Courtesy of ZOLL. limitations in the hyperbaric© Jones environment & Bartlett (flow Learning, rates LLC © Jones & Bartlett Learning, LLC <10 L/min at a depthNOT of 30 FOR feet of SALEseawater OR [fsw]). DISTRIBUTION One NOT FOR SALE OR DISTRIBUTION concern of purely pneumatic ventilators is a lack of ventilators across the globe, along with the prolifera- some alarm features such as an audible/visual patient tion of proprietary terms to describe specific modes, disconnect alarm. Another is gas consumption. Indi- has made it difficult to assure standardization of terms vidual differences in system requirements and function when the device is employed. A 2014 paper on ventila- predict© Jones the degree & Bartlett of product Learning, evaluation needed LLC to tor classification© Jones presented & Bartlett “10 maxims Learning, for understand- LLC evaluateNOT specific FOR SALE transport OR ventilators DISTRIBUTION for specific use ing modes”14NOT based FOR on a reviewSALE of OR the literatureDISTRIBUTION on environments. mechanical ventilation. The key points of the suggested Another transport ventilator, newly adopted by the taxonomy for mechanical ventilator classification are military for combat casualty scenarios, is the Impact se- presented in Box 3-7. ries of ventilators, recently acquired and offered by Zoll © Jones & (BartlettFigure 3-13 Learning,). The 731 series LLC family is air-worthy, MRI © JonesVentilator & Bartlett Variables: Learning, Breath TriggerLLC 12 NOT FOR SALEcompliant, OR and DISTRIBUTION rugged, as one may well imagine. They NOTA FOR breath SALE is one cycleOR DISTRIBUTIONof positive flow (inspiration) have been coupled with pulse oximetry from Masimo and and negative flow (expiration). Ventilators must be will likely soon use photoplethysmographic techniques able to initiate an inspiration, sustaining that inspi- of arterial waveform analysis and cardiopulmonary re- ration until some specific target parameter is met serve to more rapidly identify perfusion abnormalities and then terminate the inspiration. Put another way, ˙ shortfalls.13 ©These Jones 10-lb & units Bartlett are 8 × 12.5Learning, × 4 LLC © Jones & Bartlett Learning, LLC and DO2 a breath can be described by the changeover from inches, possess a 10-hour operational battery life, and NOT FOR SALE OR DISTRIBUTIONexpiration to inspiration, theNOT inspiratory FOR phase, SALE the OR DISTRIBUTION are alarm equipped, pressure triggered, and capable of changeover from inspiration to expiration, and the ex- assist control (A/C), SIMV (PS), and CPAP (PS). piratory phase. The mechanism by which a ventilator initiates a pa- Ventilator Terminology © Jones & Bartlett Learning, LLC tient breath© is Jonesthe trigger & variable Bartlett. The Learning, trigger can LLCbe SophisticatedNOT FOR critical SALE care OR devices DISTRIBUTION to provide invasive time (machine-initiatedNOT FOR breath)SALE or OR patient DISTRIBUTION trigger (pa- mechanical ventilation combine electrical and pneu- tient initiated). A patient-triggered breath is initiated by matic power with computer design and control. R&D patient effort. The signal used by the ventilator to begin teams of clinicians and engineers have developed nu- a patient-triggered breath may be a pressure change or merous ways we can ventilate patients. Thus, we have flow change (i.e., pressure trigger or flow trigger). Neu- © Jones & seenBartlett a proliferation Learning, of modes LLC of ventilation and a wide © Jonesrally adjusted & Bartlett ventilatory Learning, assist (NAVA) LLC is a newer mode NOT FOR SALEarray of ORterms DISTRIBUTION used to describe these newer modes. NOTof FOR ventilation SALE that OR uses DISTRIBUTION the electrical activity of the dia- The numbers of companies developing mechanical phragm to trigger a breath.

9781284139860_CH03_095_154.indd 111 21/02/19 5:37 PM 112 CHAPTER 3 Principles of Mechanical Ventilation

© Jones & Bartlett Learning, LLC © Jones & BartlettBOX 3-7 Learning, Chatburn’s LLC 10 Maxims for Understanding Modes of Ventilation14 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 1. A breath is one cycle of positive flow (inspiration) 7. There are three basic breath sequences: continu- and negative flow (expiration) defined in terms of ous mandatory ventilation (CMV), intermittent the flow-time curve. mandatory ventilation (IMV), and continuous spontaneous ventilation (CSV). 2. A breath is assis©ted Jones if the ventilator & Bartlett provides Learning, some LLC © Jones & Bartlett Learning, LLC or all of the work of breathing. There are five asicb ventilatory patterns: VC-CMV, NOT FOR SALE OR DISTRIBUTION 8. NOT FOR SALE OR DISTRIBUTION 3. A ventilator assists breathing using either pressure VC-IMV, PC-CMV, PC-IMV, and PC-CSV. control or volume control based on the equation of 9. Within each ventilatory pattern there are several motion for the respiratory system. types that can be distinguished by their target- 4. Breaths are classified according to the criteria that ing schemes (set-point [s], dual [d], servo [r], ©trigger Jones (start) & Bartlett and cycle Learning,(stop) inspiration. LLC adaptive© [a], Jones bio-variable & Bartlett [b], optimal Learning, [o], and LLC NOT FOR SALE OR DISTRIBUTION intelligent [i]).NOT FOR SALE OR DISTRIBUTION 5. Trigger variable and cycle events can be either patient or machine initiated. 10. A mode of ventilation is classified according to its control variable, breath sequence, and targeting 6. Breaths are classified as spontaneous or mandatory based on both the trigger and cycle events. scheme(s). © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Pressure Trigger inspiratory effort. Many modern mechanical ventilators Typical pressure trigger thresholds are a drop in will have a bias flow moving through the circuit during proximal airway pressure in the range of 0.5 to expiration, for example 8 L/min. If the set flow trigger is 2 L/min and the patient begins to take in a breath, the 1.5 cm H2O below baseline© Jones pressure & Bartlett (i.e., – 0.5 Learning, to LLC © Jones & Bartlett Learning, LLC circuit flow past the patient “Y” will decrease slightly. – 1.5 cm H2O). ThisNOT is accomplished FOR SALE when OR the DISTRIBUTIONpa- NOT FOR SALE OR DISTRIBUTION tient makes a sufficient inspiratory effort. A patient Once the circuit flow reaches 6 L/min, an inspiration is trigger requires patient effort and contributes to the initiated, and the ventilator will deliver a breath. Flow work of breathing (WOB). The increase in WOB caused triggering also contributes to the patient’s WOB and can by patient triggering is known as trigger work. be affected by autoPEEP. When using patient-triggered ©When Jones setting & the Bartlett ventilator’s Learning, trigger sensitivity, LLC care ventilation, ©a balanceJones is &sought Bartlett between Learning, too sensitive LLC mustNOT be taken FOR such SALE that theOR patient DISTRIBUTION can easily initiate (risk of auto-triggering)NOT FOR and SALE relatively OR insensitiveDISTRIBUTION (in- a breath with minimal effort; however, the ventilator is creased WOB and anxiety) trigger thresholds. not so sensitive as to cause the ventilator to trigger with the slightest motion at the bedside (i.e., auto trigger- Time Trigger ing). Auto triggering can result from the combination Time can be used to trigger inspiration based on the set © Jones & ofBartlett overly sensitive Learning, trigger LLCsettings and excess water in © Jonesmachine & rate.Bartlett Time- Learning,or patient-triggered LLC breaths initi- NOT FOR SALEthe ventilator OR DISTRIBUTION circuit, patient movement, or even hy- NOTated FOR by theSALE ventilator OR andDISTRIBUTION cycled by the ventilator gener- perdynamic heart beats (pressure transmission into the ally are referred to as mandatory breaths. When only ventilator circuit). Auto triggering can cause the patient time-triggered breaths occur, the term “control mode” is to rapidly become hyperinflated and patient–ventilator commonly used. When only patient-triggered breaths are asynchrony will become obvious. possible, the term “assist mode” is commonly used. When With newer ventilators,© Jones the pressure & Bartlett trigger Learning, value LLCpatient-triggered or time-triggered© Jones breaths & are Bartlett possible Learning, LLC automatically adjustsNOT for the FOR set PEEP SALE level. OR For DISTRIBUTIONex- (whichever comes first), the termNOT “assist-control FOR SALE” mode OR DISTRIBUTION ample, if the trigger sensitivity is set at –1.0 and PEEP is commonly used. If a preset tidal volume is employed, is set at 5 cm H2O, the ventilator will cycle from expira- both A/C- and control-mode ventilation are properly tion to inspiration when the proximal airway pressure termed volume-control continuous mandatory ventila- drops from +5 to +4 cm H2O. Pressure triggering may © Jones & Bartlett Learning, LLC tion (VC-CMV).© Jones If a preset & Bartlett inspiratory Learning, pressure and LLC innot function properly in the presence of autoPEEP spiratory time are employed, both A/C and control-mode dueNOT to air FORtrapping SALE and trigger OR DISTRIBUTION work may increase. The ventilation areNOT properly FOR referred SALE to OR as pressure-control DISTRIBUTION respiratory care clinician should monitor for the pres- continuous mandatory ventilation (PC-CMV). While ence of autoPEEP and take steps to reduce or eliminate the terms “assist breaths” and “control breaths” are com- autoPEEP if it is present. monly used, preferred terminology is “patient-triggered” and “time-triggered” breaths, respectively. © Jones & FlowBartlett Trigger Learning, LLC © Jones & Bartlett Learning, LLC Respiratory rate, respiratory cycle time, inspira- NOT FOR SALEFlow triggering OR DISTRIBUTION is based on a change in airflow from NOTtory FOR time, SALE expiratory OR time,DISTRIBUTION and I:E ratio are all interre- baseline during expiration caused by a patient’s lated. For instance, if during time-triggered VC-CMV,

9781284139860_CH03_095_154.indd 112 21/02/19 5:37 PM Ventilator Principles 113

© Jones &a Bartlett machine rate Learning, of 10 breaths/min LLC (f = 10) is set, the © Jonesinspiration, & Bartlett the inspiratory Learning, phase, LLCthe changeover from inspiration to expiration, and the expiratory phase. NOT FOR SALEmachine OR will DISTRIBUTIONdeliver a 10 mandatory breaths/min and NOT FOR SALE OR DISTRIBUTION the respiratory cycle time (TRC) will be 6.0 seconds When clinicians set ventilator variables such as mode; (TRC = 60 ÷ f). During VC-CMV, some ventilators al- respiratory rate; trigger effort; inspiratory flow, pres- low for setting the inspiratory time (TI) or inspiratory sure, volume, or time; and expiratory pressure they are percent time, while others allow for setting the peak in- controlling the way a breath is initiated, what happens spiratory flow rate. ©These Jones additional & Bartlett settings, Learning, along with LLCduring the inspiratory phase, ©how Jones inspiration & Bartlett is stopped, Learning, LLC inspiratory flow waveform,NOT FOR will determine SALE OR inspiratory DISTRIBUTION and what happens during theNOT expiratory FOR phase. SALE As OR DISTRIBUTION time (TI), expiratory time (TE), and I:E ratio. Expiratory noted earlier, the trigger variable refers to the method time is simply the respiratory cycle time minus the in- by which inspiration begins (also known as the change- spiratory time (TE = TRC – TI). During VC-CMV, when over from expiration to inspiration). The cycle variable using ventilators with tidal volume, peak inspiratory refers to the method by which inspiration is cycled off or stops, also known as the changeover from inspiration flow,© Jonesand flow & waveformBartlett controls, Learning, TI will decrease LLC with © Jones & Bartlett Learning, LLC an increase in peak flow or a decrease in VT. A change to expiration. Breaths may be cycled by time, pressure NOT FOR SALE OR DISTRIBUTION peak airwayNOT pressure FOR SALE [PAW] OR DISTRIBUTION from a down-ramp flow waveform to a square wave flow (i.e., ), volume, or flow (e.g., waveform will also decrease TI. In a similar fashion, TI percent of peak inspiratory flow). Thus, a ventilator- will increase with a decrease in peak flow, increase in delivered breath may be volume cycled, pressure cycled, VT, or a change from a square wave flow waveform to a time cycled, or flow cycled. It should also be noted that © Jones & down-rampBartlett Learning, flow waveform. LLC © Jonesa breath & mayBartlett be pressure Learning, limited and LLC pressure cycled, pressure limited and time cycled (e.g., pressure control NOT FOR SALEChanges OR in DISTRIBUTION TI will affect ET and I:E ratio (assuming NOT FOR SALE OR DISTRIBUTION a constant respiratory cycle time). Respiratory rate and ventilation), or pressure limited and flow cycled (e.g., respiratory cycle time may vary with patient-triggered pressure support ventilation), as described below. breaths (e.g., assist-control ventilation); as respiratory Mandatory breaths occur when the ventilator de- rate increases respiratory cycle time will decrease and livers the same breath type with each cycle. That is, vice versa. TI, TE, and© I:E Jones ratio be & discussed Bartlett further Learning, in LLCthe ventilator controls how the© breathJones begins & Bartlett and/ Learning, LLC the next section. NOT FOR SALE OR DISTRIBUTIONor ends. Spontaneous breathsNOT occur FOR when theSALE start OR DISTRIBUTION and end of inspiration are determined by the patient, Ventilator Variables: Breath Cycle independent of other ventilator settings. Thus, ventilator cycling of a mandatory breath is different from Breathing is cyclic in nature: inspiration cycles into ex- patient-cycled ventilation. piration, and expiration cycles into inspiration. When observing© Jones spontaneous & Bartlett respiration, Learning, we can LLC certainly © Jones & Bartlett Learning, LLC alterNOT our tidalFOR volumes, SALE inspiratory OR DISTRIBUTION times, expiratory Patient CyclingNOT FOR SALE OR DISTRIBUTION times, and flow rates. At rest, our ventilatory pattern is Spontaneous breaths are initiated by the patient and the determined by a complex interplay between multiple patient determines when the end of inspiration occurs regions in the brain (e.g., medullary respiratory group, (i.e., breaths are patient triggered and patient cycled). ventral respiratory group, apneustic center, pneumo- Most modern ventilators allow for spontaneous breath- © Jones & taxicBartlett center, Learning, and central chemoreceptors) LLC and by af- © Jonesing, with & Bartlett(or without) Learning, inspiratory pressureLLC augmenta- NOT FOR SALEferent feedback OR DISTRIBUTION from sensory receptors and peripheral NOTtion FOR and SALE with (or OR without) DISTRIBUTION an elevated baseline pressure chemoreceptors (e.g., proprioreceptors, lung reflexes, during the expiratory phase (i.e., with or without PEEP/ and peripheral chemoreceptors) to maintain homeosta- CPAP). The key point is that with spontaneous breath- sis. Our inspiratory to expiratory cycling, in most nor- ing through the ventilator circuit, the patient controls mal situations, is unrelated to conscious thought. We the initiation of the breath (i.e., patient triggered to do have conscious control© Jones of our & breathing Bartlett (e.g., Learning, corti- LLCinspiration) as well as breath ©termination Jones & (i.e., Bartlett patient Learning, LLC cal control of voluntaryNOT breathing), FOR SALE but normally OR DISTRIBUTION this cycled to expiration). With patient-cycledNOT FOR spontane-SALE OR DISTRIBUTION control is not exercised. Occasionally, our breathing is ous breathing through the ventilator circuit, the patient brought to our conscious awareness, especially in cases is rarely left without any form of support. The most where we become short of breath. Recall that dyspnea is familiar forms of support include inspiratory pressure simply the conscious awareness of difficult breathing. © Jones & Bartlett Learning, LLC augmentation© Jones(pressure & support Bartlett ventilation Learning, [PSV] orLLC Cycle Variables automatic to compensation [ATC]) and increased base- NOT FOR SALE OR DISTRIBUTION line airway NOTpressure FOR (PEEP SALE or CPAP). OR LowDISTRIBUTION to moder- With mechanical ventilation, the respiratory cycle is ate levels of pressure support (e.g., 5 to 15 cm H2O) or determined by the method of initiating or triggering ATC can be used to relieve the imposed WOB due to inspiration, inspiratory phase events (i.e., inspiratory increased airway resistance of the endotracheal or tra- © Jones & pressures,Bartlett flows, Learning, and volumes), LLC the method by which © Jonescheostomy & Bartlett tube. Higher Learning, levels of PSVLLC (e.g., 15 to 25 cm inspiration stops and expiration begins, and what oc- H2O) can be used to provide higher levels of ventilatory NOT FOR SALEcurs during OR expiration. DISTRIBUTION Put another way, breaths can NOTsupport FOR SALEand are sometimesOR DISTRIBUTION employed as part of a venti- be described by the changeover from expiration to lator weaning protocol.

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© Jones & BartlettAs noted, Learning, pressure support LLC (PS) or automatic tube © Jonesdecrease & Bartlettin lung compliance Learning, or increase LLC in airway resis- compensation [ATC] may be applied during “spontane-NOTtance, FOR the SALE ventilator OR will DISTRIBUTION cycle to exhalation earlier and NOT FOR SALEous” breaths OR andDISTRIBUTION support some of the work of inspira- tidal volume will be reduced. Conversely, if there are tion. When spontaneously breathing patients inspire improvements in lung compliance (e.g., diuretic effects with PSV or ATC, they will begin to exhale based on on lung liquid) or airway resistance (e.g., bronchodilator their natural respiratory cycle. With PSV, inspiration is administration) with pressure cycling, higher than in- terminated when a specific© Jones flow & criterionBartlett is reached.Learning, For LLCtended tidal volumes may be ©delivered. Jones Pressure & Bartlett cycling Learning, LLC example, early versionsNOT of PSV FOR would SALE cycle OR from DISTRIBUTION inspi- generally is not used in the modernNOT FORintensive SALE care unit, OR DISTRIBUTION ration to expiration when the inspiratory flow dropped except as a backup safety feature during VC ventilation to 25% of the peak flow or 5 L/min. Newer ventila- by providing a pressure limit for VC breaths. Pressure tors allow the operator to adjust the flow termination cycling should not be confused with pressure-control criteria (i.e., expiratory trigger or expiratory sensitiv- ventilation (see below). ity ©[E SENSJones]). During & Bartlett PSV, cycling Learning, to exhalation LLC during © Jones & Bartlett Learning, LLC a spontaneousNOT FOR breath SALE can OR be influenced DISTRIBUTION by adjusting Time CyclingNOT FOR SALE OR DISTRIBUTION the level of inspiratory pressure support, adjusting the Mandatory breath time cycling has been available on breath contour (e.g., adjusting rise time), or adjusting certain ventilators for many years. Modern ventilators the flow termination criterion. These adjustments affect used in the pressure-control (PC) mode are typically patient comfort and patient–ventilator synchrony and time cycled. For example, with pressure-controlled con- © Jones & shouldBartlett be optimized Learning, for individual LLC patients. © Jonestinuous & mechanical Bartlett Learning,ventilation (PC-CMV), LLC the operator NOT FOR SALE OR DISTRIBUTION NOTsets FOR the SALErespiratory OR rate, DISTRIBUTION percent inspiratory time, and Mandatory Breath Cycling inspiratory pressure limit. With PC-CMV, inspiration is Mandatory breaths occur when the ventilator delivers patient or time triggered (assist-control). During inspi- the same breath type with every breath. With mandatory ration, airway pressure rises to a preset value. Inspira- breaths the start and/or end of inspiration is determined tion is then time cycled to expiration. by the ventilator independent© Jones of &the Bartlett patient. Put Learning, another LLCSome critical care ventilators© Jonesallow for &setting Bartlett the Learning, LLC way, the machine triggersNOT and/or FOR cycles SALE the OR breath; DISTRIBUTION the inspiratory time or inspiratoryNOT percent FOR time SALE in the VC OR DISTRIBUTION patient does not control breath timing (i.e., frequency or mode. In such cases, these ventilators are technically inspiratory time).14 Mandatory breaths may be time or time cycled, but adjust delivered flow during the pre- patient triggered and pressure or volume controlled (PC scribed inspiratory time interval to assure the set volume or VC). Mandatory breaths may be cycled from inspira- is delivered. For these ventilators, short inspiratory times tion© to Jones exhalation & Bartlettusing either Learning, time, pressure, LLC or volume. (TI) translate© into Jones higher & inspiratory Bartlett flows Learning, and vice LLCversa. EarlyNOT pressure-limited FOR SALE ventilators OR DISTRIBUTION (e.g., Bennett PR-2) al- AdjustmentsNOT of FOR the set SALE inspiratory OR time DISTRIBUTION (or inspira- lowed for time- or patient-triggered breaths that cycled tory percent time) requires consideration of the pa- to expiration when the flow decreased to 1 to 3 L/min, tient’s disease state. Normal lungs can be ventilated thus allowing for flow-cycled, assist-control ventilation; with a normal inspiratory time of 0.60 to 1.0 seconds with the rate set the PR-2 included a backup time cycle (adults) with an I:E ratio of 1:2 or lower. With obstruc- © Jones & andBartlett most clinicians Learning, would LLC consider this a form of man-© Jonestive lung & Bartlettdisease, decreased Learning, TI, increased LLC TE, and lower NOT FOR SALEdatory breath OR DISTRIBUTION cycling. NOTI:E FOR ratio SALE (e.g., I:E OR = 1:3 DISTRIBUTION or 1:4) may be used to provide additional time for exhalation to prevent air trapping, Pressure Cycling and avoid hyperinflation and autoPEEP Increased TI may improve the distribution of the inspired gas and With pressure cycling, the ventilator switches from oxygen transfer across the lung. With acute restric- inspiration to exhalation when a clinician-defined in- © Jones & Bartlett Learning, LLCtive lung disease (e.g., ARDS),© higher Jones I:E ratios& Bartlett with Learning, LLC spiratory pressure is attained. Early, pressure-cycled = NOT FOR SALE OR DISTRIBUTIONTE approaching or exceeding NOTTI (I:E FOR 1:1 orSALE higher) OR DISTRIBUTION ventilators such as the Bird Mark Series (Mark 7, 10, 14) may be used. Pressure-control inverse-ratio ventilation were sometimes used in the emergency department, re- (PC-IRV) is sometimes useful in cases of severe, acute, covery room, and intensive care unit to provide ventila- restrictive lung disease (e.g., ARDS). PC-IRV aids in vol- tory support. Pressure cycling can also occur during VC ume distribution throughout the lung fields that may be ventilation© Jones when & aBartlett preset pressure Learning, limit is reached,LLC to compromised© Jonesby heterogeneity & Bartlett of regional Learning, compliance. LLC protectNOT the FOR patient SALE from excessivelyOR DISTRIBUTION high pressures such Figure 3-14NOT illustrates FOR time-cycled SALE OR PC-IRV DISTRIBUTION. as may occur with coughing or fighting the ventilator. As noted, early pressure-limited, flow-cycled ventilators such as the Bennett PR-2 were also sometimes used to Volume Cycling provide short-term ventilatory support in the assist- Volume cycling occurs when a clinician-set tidal volume © Jones & controlBartlett or control Learning, modes LLC(i.e., patient or time triggered).© Jonesis reached, & Bartlett cycling the Learning, ventilator to LLC expiration. With vol- NOT FOR SALEWith OR pressure DISTRIBUTION cycling, the cycle pressure is constant,NOT ume FOR cycling, SALE airway OR pressure DISTRIBUTION is variable and dependent but the tidal volume is variable. For example, if there is a on the patient’s lung mechanics. With volume-cycled

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© Jones & Bartlett Learning, LLC © JonesWith & IMVBartlett or SIMV, Learning, mandatory LLC breaths are de- NOTlivered FOR atSALE a preset OR rate, DISTRIBUTION allowing for spontaneous NOT FOR SALE OR DISTRIBUTION breathing to occur in between mandatory breaths. Mandatory breaths are typically pressure controlled or

essure volume controlled. Spontaneous breaths may be pres- Pr sure augmented by providing low to moderate levels of © Jones & Bartlett Learning, LLCpressure support. In combination© Jones with IMV & Bartlett or SIMV, Learning, LLC NOT FORTime SALE OR DISTRIBUTIONpressure support is generally NOTused as FOR an adjunct SALE to over-OR DISTRIBUTION come the imposed WOB (WOBI) due to the artificial Figure 3-14 Pressure-Controlled Inverse-Ratio Ventilation. airway. As noted above, PSV levels to overcome WOBI during spontaneous breathing are generally in the range of 5 to 15 cm H2O. ventilation, decreased lung compliance or increased As described earlier, flow cycling is dependent on airway© Jones resistance & willBartlett result inLearning, an increased LLC PIP. Put an- © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION a decrease inNOT inspiratory FOR flowSALE rate, OR often DISTRIBUTION as a set per- other way, volume is constant, and pressure is variable. centage of a peak inspiratory flow. For example, if flow The risk of pulmonary barotrauma using volume cycling cycling is set to 25% of the peak flow, the ventilator will with high airway pressures led (in part) to the develop- cycle to exhalation as the inspiratory flow rate dimin- ment of pressure-control ventilation and later, dual and ishes by 75%. adaptive breath targeting. Flow cycling generally functions well with variable © Jones & BartlettAcute respiratory Learning, distress LLC syndrome (ARDS) is an in-© Jones & Bartlett Learning, LLC breathing patterns as may occur with spontaneous ven- NOT FOR SALEflammatory OR lungDISTRIBUTION condition resulting in leakage of bloodNOT FOR SALE OR DISTRIBUTION tilation. Flow cycling is sometimes subject to difficulties and plasma into the alveoli, markedly reduced lung during ventilation of restrictive and obstructive lung compliance, and serious oxygenation problems. In the disease. For example, the effects of flow cycling onI T 1970s, 1980s, and early 1990s it was common practice to will vary with pulmonary mechanics. With restrictive ventilate ARDS patients with large tidal volumes in the lung disease (e.g., decreased lung compliance), early range of 10 to 15 mL/kg© Jones IBW. With & VCBartlett ventilation, Learning, high LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONtermination of the inspiratoryNOT phase FOR may occur SALE due OR to a DISTRIBUTION PIPs were often required to deliver tidal volumes in this rapidly diminished inspiratory flow rate. With obstruc- range. With the advent of the ARDS Network in 1994, it tive lung disease, prolongation of the inspiratory phase became apparent that ventilation using these large tidal > may occur due to a more slowly decreasing expiratory volumes ( 10 mL/kg) and high PEEP with volume cy- flow.16 Accommodation of these problems can be made cling resulted in increased risk of ventilator-associated through patient assessment, waveform analysis, modi- lung© injury Jones (VALI) & Bartlett and increased Learning, mortality. LLC Studies © Jones & Bartlett Learning, LLC fication of the inspiratory rise time, and adjustment sinceNOT have FOR shown SALE that alternative OR DISTRIBUTION ventilatory strategies NOT FOR SALE OR DISTRIBUTION of ventilator flow termination criteria (e.g., expiratory including pressure-controlled ventilation, permissive hy- sensitivity [ESENS] or expiratory trigger sensitivity [ETS]). percapnia, prone position ventilation, inverse ratio ven- Patient–ventilator synchrony and timing issues of flow tilation, airway pressure release ventilation, dual-control cycling in the compromised patient require a knowl- modes, and high-frequency forms of mechanical ven- Figure 3-15 © Jones & Bartlett Learning, LLC 15 © Jonesedgeable & Bartlettrespiratory Learning, care clinician. LLC illus- tilation can be effective with ARDS patients. Current trates typical flow, pressure, and volume–time curves treatment of ARDS includes treatment of the underlying NOT FOR SALE OR DISTRIBUTION NOTseen FOR with SALE patient-triggered, OR DISTRIBUTION flow-cycled, pressure- cause, early use of antibiotics for pneumonia or sepsis, support ventilation. and the use of smaller tidal volumes (VT 4 to 8 mL/kg ≤ Some ventilators offer an option that incorporates IBW) delivered at low pressures ( 30 cm H2O) from the flow cycling with a volume target (e.g., volume support ventilator (aka lung protective ventilation). © Jones & Bartlett Learning, LLCventilation [VS]) in which the© ventilator Jones automatically& Bartlett Learning, LLC adjusts ventilator cycling based on previous breath Flow Cycling NOT FOR SALE OR DISTRIBUTIONanalysis in order to maintain NOTtidal volume. FOR 17SALE OR DISTRIBUTION Most modern critical care ventilators incorporate the pressure-support ventilation (PSV) option to provide . Operator Interface Pressure support may be used as a standalone mode in which© Jones each breath& Bartlett is patient Learning, triggered, pressure LLC Ventilator controls© Jones currently & Bartlett use combinations Learning, of LLC limited,NOT and FOR flow SALE cycled, ORor as DISTRIBUTION an option with the buttons, switches,NOT FORand microprocessor-generated SALE OR DISTRIBUTION use of intermittent mandatory ventilation (IMV) or touch-screen simulations of control knobs or icons and synchronized intermittent mandatory ventilation (SIMV). the occasional multifunction dial for the adjustment of As a standalone mode, PSV levels are adjusted to ensure ventilator functions. Fifty years ago, ventilators like the adequate tidal volumes (VT 4 to 8 mL/kg) and satisfac- Puritan Bennett MA-1 were introduced with rheostat/ © Jones & toryBartlett respiratory Learning, rates (f ≤ LLC 25 breaths/min). For ventila-© Jonespotentiometer & Bartlett operated Learning, dials to adjust LLC tidal volume, NOT FOR SALEtor weaning, OR theDISTRIBUTION PSV level can be reduced gradually, inNOT rate, FOR and SALE Fio2. PEEP OR systemsDISTRIBUTION were soon added followed a stepwise fashion, based on the patient’s response. by reservoir bags, H-valves, and then demand flow

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© Jones & Bartlett40 Learning, LLC © Jones & Bartlett Learning, LLC 30 NOT FOR SALE20 OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 10 0 –10 –20 Flow (L/min) Flow –30 –40 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC –50 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 24 O)

2 20 16 12 © Jones8 & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC

essure (cm H essure NOT4 FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Pr 0 600 500 © Jones & Bartlett400 Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE300 OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION lume (mL) 200 Vo 100 0 0246135798 10 11 12 13 14 © Jones & Bartlett Learning,Time LLC (seconds) © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Figure 3-15 Flow, Pressure, and Volume–Time Curves During Pressure Support Ventilation. Pressure support is patient triggered (note the pressure drop that begins inspiration) and flow cycled (note the decreasing flow waveform and near square-wave pressure waveform). Hess DR, Kacmarek RM. Essentials of Mechanical Ventilation, 2nd ed. New York, NY: McGraw Hill; 2002.

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION systems for IMV. For many years, Hollywood continued to display the MA-1 in its hospital scenes with the attached bellows spirometer moving up and down simu- lating positive pressure ventilation. Today’s ventilators © Jones & displayBartlett breath-to-breath Learning, numericalLLC changes, sophisti- © Jones & Bartlett Learning, LLC NOT FOR SALEcated graphics OR DISTRIBUTION with adjustable time scales, pressure– NOT FOR SALE OR DISTRIBUTION volume curves, and a host of screen options and views to adjust and monitor ventilation. The myriad of possible screen adjustments varies as widely as the manufacturers of mechanical ventilators. In general, the user interface is divided into© Jones sections &of machineBartlett set Learning, param- LLC © Jones & Bartlett Learning, LLC eters, patient-measuredNOT variables, FOR SALEalarm settings, OR DISTRIBUTION and NOT FOR SALE OR DISTRIBUTION graphics. Pressures (PIP, Paw, and PEEP), volumes (in- ˙ Figure 3-16 Lung Mechanics as Displayed on the Dräger spiratory VT, expiratory VT, and VE, both spontaneous and machine delivered), flow and time variables (peak Evita V500. At a glance, the respiratory therapist can make observations of worsening Raw and CL as given numerically and a flow, respiratory rate [f], I:E ratio, and IT ) can be dis- thickening outline of the major airways and lungs and chest wall. played© Jones both numerically & Bartlett and Learning,via user-defined LLC graphics. © Jones & Bartlett Learning, LLC (1 mbar = 1.02 cm H2O) SomeNOT ventilators FOR SALE have gone OR to DISTRIBUTION“smart” graphic displays © Dragerwerk AG NOT& Co. KGaA. FOR Image reprinted SALE with permission. OR DISTRIBUTION of lung function to provide easy recognition of changes in lung compliance or airways resistance (Figure 3-16). 14 Ventilator Classification or Taxonomy ventilator mode (Box 3-7). The mode of ventilation is © Jones & Bartlett Learning, LLC © Jonesdetermined & Bartlett by the control Learning, variable, LLC breath sequence, NOT FOR SALEUsing Chatburn’s OR DISTRIBUTION strategy for ventilator classifica- NOTand FOR targeting SALE scheme OR DISTRIBUTIONemployed. The common control tion, the 10th maxim refers to the determination of a variables are pressure or volume for the primary breath.

9781284139860_CH03_095_154.indd 116 21/02/19 5:37 PM Ventilator Modes 117

© Jones &The Bartlett primary Learning, breath is defined LLC as either the spontaneous© Jones ventilatory& Bartlett parameters. Learning, For example,LLC the ventila- breath in continuous spontaneous ventilation (CSV), tor may automatically adjust pressure to achieve NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION the mandatory breath in continuous mandatory ventila- an average VT over several breaths. tion (CMV), or the mandatory breath in intermittent ■■ Biovariable (b) targeting schemes allow the ven- mandatory ventilation (IMV). With CSV, all breaths tilator to introduce some deviation from the set are spontaneous. With CMV, all breaths are manda- point of the control variable (pressure or volume) tory. With IMV, spontaneous© Jones breaths & Bartlett are interspersed Learning, LLC to mimic the variability© seen Jones in normal, & Bartlett spontane- Learning, LLC with mandatory breaths.NOT Using FOR the SALE breath sequenceOR DISTRIBUTION ous respiration. NOT FOR SALE OR DISTRIBUTION of either CSV, CMV, or IMV coupled with the control ■■ Optimal (o) targeting schemes allow ventilator variable of either pressure or volume, the clinician auto-adjustments that may alter variables such as can describe the basic mode of ventilation being em- respiratory rate, flow, or volume to improve on ployed. Using this system, there are five basic modes of anticipated outcomes (e.g., lowered WOB). ventilation available:© Jones & Bartlett Learning, LLC ■■ Intelligent© Jones (i) targeting & Bartlett schemes Learning,use “artifi- LLC cial intelligence programs such as fuzzy logic, NOT■■ FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Volume-control–continuous mandatory ventila- rule-based expert systems, and artificial neural tion (VC-CMV). This mode is commonly referred networks” to respond to changing patient lung to as assist-control volume ventilation. compliance, resistance, or effort. ■■ Volume-control–intermittent mandatory ventilation (VC-IMV). This mode is commonly referred to Figure 3-17 provides a simplified taxonomy for clas- © Jones & Bartlettas IMV Learning, or SIMV volume LLC ventilation (aka V-SIMV).© Jonessifying & ventilator Bartlett modes. Learning, LLC NOT FOR SALE■■ Pressure-control–continuous OR DISTRIBUTION mandatory ventila- NOT FORDifferent SALE ventilator OR DISTRIBUTION manufacturers often use different tion (PC-CMV). This mode is commonly referred proprietary names for specific modes as illustrated in to as assist-control pressure-control ventilation Table 3-1. Hopefully, time and consensus will find reso- (PCV). lution to the conflict between proprietary names and 18 ■■ Pressure-control–intermittent mandatory ventila- actual function. tion (PC-IMV).© This Jones mode & is Bartlettcommonly Learning, referred LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION to as SIMV pressure-control ventilation (aka Ventilator Modes P-SIMV). ■■ Pressure-control–continuous spontaneous ven- A ventilator mode may be described by its control vari- tilation (PC-CSV). The most common form of able, breath sequence, and targeting scheme employed. this mode is standalone pressure-support ventila- That said, there has been an extraordinary proliferation © Jonestion (PSV). & Bartlett Learning, LLC of ventilator© modes Jones available, & Bartlett along with Learning, an array of LLC NOT FOR SALE OR DISTRIBUTION often-conflictingNOT FORmanufacturers’ SALE ORterminology DISTRIBUTION to de- The next step in ventilator classification is a deter- scribe these modes. We will focus our discussion on the mination of the ventilator breath targeting scheme, for five basic modes of ventilation described below. both the primary breath and, if applicable, the secondary (spontaneous) breath. The targeting scheme distin- Continuous Mandatory Ventilation © Jones & guishesBartlett one Learning, ventilatory pattern LLC from another and is the© Jones & Bartlett Learning, LLC The control variable with continuous mandatory ven- NOT FOR SALEmethod ORused DISTRIBUTIONby the ventilator to reach specific param-NOT FOR SALE OR DISTRIBUTION eters. The lowercase letters shown below (s, d, r, a, b, tilation [CMV] can be either pressure or volume, but o, and i) describe seven different targeting schemes cur- there are no entirely spontaneous breaths. Put another rently used by modern mechanical ventilators:14 way, with CMV, every breath is a mandatory breath. The patient may trigger inspiration, but every breath is ■■ Set-point (s) targeting© Jones schemes & Bartlett allow the Learning,operator LLCmachine cycled to expiration.© Commonly Jones & referred Bartlett to Learning, LLC to set all waveform parameters. In volume-control as assist-control ventilation, the patient can trigger or mode, the operatorNOT sets FOR volume SALE and flowOR DISTRIBUTIONwave- “assist” the ventilator-deliveredNOT primary FOR breath. SALE In theOR DISTRIBUTION forms. In pressure-control mode, the operator sets event of no spontaneous effort during the respiratory the pressure waveform. cycle time, the ventilator will deliver a “control” breath ■■ Dual (d) targeting schemes refer to the possibility that is time triggered. © Jonesof within-breath & Bartlett variations Learning, of volume LLC or pressure For volume-control–continuous© Jones & Bartlett mandatory Learning, ven- LLC NOTcontrol. FOR SALE OR DISTRIBUTION tilation (VC-CMV),NOT FOR the control SALE variable OR DISTRIBUTION is volume ■■ Servo (r) targeting schemes utilize ventilator-sensing and every breath is mandatory. While the patient can technology to adjust supporting pressures based on initiate inspiration, the clinician-defined tidal volume the patient’s inspiratory effort. is delivered with each breath. Similarly, for pressure- ■■ Adaptive (a) targeting schemes can use signal control–continuous mandatory ventilation (PC-CMV), © Jones & Bartlettaveraging Learning, of previous LLC tidal breaths coupled © Jonesthe control & Bartlett variable isLearning, pressure. The LLC patient can initiate NOT FOR SALEwith OR auto-adjusting DISTRIBUTION (e.g., pressure) variables to NOTthe FOR breath, SALE but each OR inspiration DISTRIBUTION is provided at a clinici an- make alterations to maintain the desired patient defined inspiratory pressure. If no spontaneous breaths

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Figure 3-17 A Simplified Taxonomy for Classifying Modes. Reproduced from Mireles-Cabodevila, E., Hatipoglu, U., Chatburn, R. A rational framework for selecting modes of ventilation. Respir Care. 2013;58(2):348–366. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

9781284139860_CH03_095_154.indd 118 26/02/19 1:06 PM Ventilator Modes 119

A/C volume control (VC-CMVs*) Bilevel with pressure support (PC-IMVs, s) SIMV volume control with pressure support (VC-IMVs, s) Bilevel with tube compensation (PC-IMVs, r) SIMV volume control with© tube Jones compensation & Bartlett (VC-IMVs, Learning,r) LLCSIMV volume control plus with pressure© supportJones (PC-IMV & Bartletta, s) Learning, LLC A/C pressure control (PC-CMVs) SIMV volume control plus with tube compensation (PC-IMVa, r) A/C volume control plusNOT (PC-CMV FORa) SALE OR DISTRIBUTIONSpontaneous pressure support (PC-CSVy)NOT FOR SALE OR DISTRIBUTION SIMV pressure control with pressure support (PC-IMVs, s) Spontaneous tube compensation (PC-CSVr) SIMV pressure control with tube compensation (PC-IMVs, r) Spontaneous proportional assist (PC-CSVr) Spontaneous volume support (PC-CSVa)

Dräger© Jones Evita XL & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC CMVNOT (VC-CMV FORs) SALE OR DISTRIBUTION Pressure-controlNOT ventilation FOR plus withSALE pressure OR support DISTRIBUTION (PC-IMVs, s) CMV with pressure-limited ventilation (VC-CMVd) APRV (PC-IMVs, s) SIMV (VC-IMVs, s) Mandatory minute volume with AutoFlow (PC-IMVa, s) SIMV with automatic tube compensation (VC-IMVs, sr) SIMV with AutoFlow (PC-IMVa, s) SIMV with pressure-limited ventilation (VC-IMVd, s) Mandatory minute volume with AutoFlow and tube compensation SIMV with pressure-limited ventilation and automatic tube (PC-IMVar, sr) © Jones & Bartlettcompensation Learning, (VC-IMVd, sr )LLC © JonesSIMV with & AutoFlow Bartlett and tube Learning, compensation LLC (PC-IMVar, sr) NOT FOR SALEMandatory OR minute DISTRIBUTION volume ventilation (VC-IMVa, s) NOTPressure-control FOR SALE ventilation OR plusDISTRIBUTION with pressure support and tube Mandatory minute volume ventilation with automatic tube compensation (PC-IMVsr, sr) compensation (VC-IMVa, sr) APRV with tube compensation (PC-IMVsr, sr) Mandatory minute volume with pressure-limited ventilation CPAP with pressure support (PC-CSVs) (VC-IMVda, s) SmartCare (PC-CSVi) Mandatory minute volume with pressure-limited ventilation and CPAP with pressure support and tube compensation (PC-CSVsr) automatic tube compensation© Jones (VC-IMV &da, Bartlett sr) Learning, LLC © Jones & Bartlett Learning, LLC Pressure-control ventilation plus assisted (PC-CMVs) CMV with AutoFlow (PC-CMVNOTa) FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION CMV with AutoFlow and tube compensation (PC-CMVar)

Hamilton Medical G5

Synchronized controlled mandatory ventilation (VC-CMVs) Adaptive pressure ventilation (CMV PC-CMVa) SIMV© Jones(VC-IMVs, s &) Bartlett Learning, LLC Adaptive pressure© Jonesventilation CMV& Bartlett with tube-resistance Learning, LLC SIMVNOT with FORtube-resistance SALE compensation OR DISTRIBUTION (CV-IMVs, sr) compensationNOT (PC-CMV FORar) SALE OR DISTRIBUTION Pressure control (CMV PC-CMVs) Pressure control CMV with tube-resistance compensation (PC-CMVsr) Pressure (SIMV PC-IMVs, s) NIV-spontaneous timed (PC-IMVs, s) Nasal CPAP with pressure support (PC-IMVs, s) APRV (PC-IMVs, s) © Jones & BartlettDuoPAP (PC-IMV Learning,s, s) LLC © Jones & Bartlett Learning, LLC NOT FOR SALEAdaptive OR pressure DISTRIBUTION ventilation (SIMV PC-IMVa, s) NOT FOR SALE OR DISTRIBUTION Adaptive pressure ventilation SIMV with tube-resistance compensation (PC-IMVar, sr) ASV (PC-IMVoi, oi) IntelliVent-ASV (PC-IMVoi, oi) ASV with tube-resistance compensation (PC-IMVoir, oir) IntelliVent-ASV with tube-resistance© Jones compensation & Bartlett (PC-IMV Learning,oir, oir) LLC © Jones & Bartlett Learning, LLC Pressure SIMV with tube-resistance compensation (PC-IMVsr, sr) APRV with tube-resistanceNOT compensation FOR SALE(PC-IMVsr, OR sr) DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Spontaneous with tube-resistance compensation (PC-CSVr) Spontaneous (PC-CSVs) NIV G©etinge Jones Servo-i & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC VolumeNOT control FOR (VC-IMV SALEd, d) OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION SIMV (volume control) (VC-IMVd, d) Automode (volume control to volume support) (VC-IMVd, a) Pressure control (PC-CMVs)

(Continues) © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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© Jones & BartlettTABLE 3-1 Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALEVentilator OR Modes DISTRIBUTION Available on Common ICU Ventilators:NOT Manufacturer’s FOR SALE Mode OR Name DISTRIBUTION (Classification) Continued( ) Pressure-regulated volume control (PC-CMVa) SIMV (pressure control) (PC-IMVs, s) BiVent (PC-IMVs, s) Automode (pressure control to pressure support) (PC-IMVs, s) SIMV pressure-regulated© volume Jones control & (PC-IMV Bartletta, s) Learning, LLC © Jones & Bartlett Learning, LLC Automode (pressure-regulated volume control to volume support) (PC-IMVa, a) NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Spontaneous with CPAP (PC-CSVs) Pressure support (PC-CSVs) Neurally adjusted ventilatory assist (PC-CSVr) Volume support (PC-CSVa)

A/C,© assist-control; Jones &APRV, Bartlett airway pressure Learning, release ventilation; LLC ASV, adaptive support ventilation; CMV, ©continuous Jones mandatory & Bartlett ventilation; CPAP, Learning, continuous positive LLC airwayNOT pressure; FOR CSV, SALEcontinuous spontaneousOR DISTRIBUTION ventilation; IMV, intermittent mandatory ventilation; NIV,NOT noninvasive FOR ventilation; SALE PC, pressure OR control;DISTRIBUTION SIMV, synchonized intermittent mechanical ventilation; VC, volume control. *Targeting schemes are represented by single lowercase letters: s = set-point, r = servo, a = adaptive, d = dual, i = intelligent, and o = optimal. Combinations include: sr = set-point with servo, da = dual with adaptive, as = adaptive with set-point, ar = adaptive with servo, oi = optimal with intelligent, and oir = optimal with intelligent and servo. Data from Chatburn RL, El-Khatib M, Mireles-Cabodevila E. A taxonomy for mechanical ventilation: 10 fundamental maxims. Respir Care. 2014;59(11): © Jones & Bartlett1747–1763. doi:10.4187/respcare.03057.Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION occur to initiate inspiration, both VC-CMV and PC- The National Institutes of Health Heart, Lung, and CMV will deliver a time-triggered inspiration, at a Blood Institute’s ARDS Clinical Network (ARDSNet) frequency normally determined by the set (mandatory) protocol for ventilation of patients with ARDS states respiratory rate. Most modern critical care ventilators that any ventilator mode may be used.19 Tidal volume offer VC-CMV and ©PC-CMV, Jones along & Bartlett with a host Learning, of other LLCis initiated at 8 mL/kg of PBW© andJones then &reduced Bartlett by Learning, LLC mode options. It shouldNOT be notedFOR that SALE a few OR ventilators DISTRIBUTION 1 mL/kg at intervals of 2 hoursNOT (or less)FOR until SALE reaching OR DISTRIBUTION use set TI and TE to determine the mandatory, time- 6 mL/kg with Pplateau ≤ 30 cm H2O. Respiratory rate cycled rate and I:E ratio (e.g., pNeuton mini and Smiths is adjusted to achieve an acceptable minute ventila- Medical Pneupac babyPAC 100). tion and pH. PEEP and Fio2 are titrated using PEEP With VC-CMV, if lung mechanics change (compli- tables to obtain a Pao2 of 55 to 80 mmHg or Spo2 of ance© orJones resistance), & Bartlett airway pressure Learning, will vary. LLC A wors- 88% to 95%.© Jones & Bartlett Learning, LLC eningNOT lung FOR condition SALE in VC-CMV OR DISTRIBUTION will result in higher Many differentNOT FOR ventilator SALE modes OR and DISTRIBUTION adjunctive tech- peak and mean airway pressures and increased risk of niques have been tried to improve outcomes in ARDS pulmonary barotrauma. Improvements in lung mechan- since the mid-1970s. Although equivocal results on ics during VC-CMV will result in lower ventilatory mortality persist, the use of prone positioning to im- pressures. prove aeration of compromised lung fields in the ARDS © Jones & BartlettWith PC-CMV, Learning, tidal volume LLC will vary with changes © Jonespatient & may Bartlett be helpful. Learning,20 In a 2006 LLC study, Mancebo NOT FOR SALEin lung mechanics.OR DISTRIBUTION In this mode, as compliance is NOTrandomized FOR SALE 136 ORpatients DISTRIBUTION with severe ARDS to either su- decreased or airway resistance increased, VT is re- pine or prone position and showed a modest reduction duced. Hypoventilation and respiratory acidosis with in mortality from 58% supine to 43% prone.21 Although worsening hypoxemia may occur. Alternatively, with the results were not statistically significant, the trend PC-CMV, if compliance and resistance improve, tidal suggested a role for the prone positioning during me- volume will increase,© possibly Jones resulting & Bartlett in a respiratory Learning, LLCchanical ventilation of the ARDS© Jones patient. &A moreBartlett recent Learning, LLC alkalosis. With a formNOT of PC-CMV FOR SALE known asOR pressure- DISTRIBUTIONstudy, known as the PROSEVANOT (Proning FOR Severe SALE ARDS OR DISTRIBUTION control–inverse-ratio ventilation (PC-IRV) the control Patients) trial, used VT-matched (6 mL/kg) patients as- variable is pressure and the I:E ratio is greater than 1:1 signed to either prone or supine positions, and found (e.g., 1.5:1, 2:1). PC-IRV is sometimes used in patients a reduction in mortality from 32% supine to 16% while with ARDS. In ARDS, there are variations in regional prone.22 Recall that the heart lies close to the sternum lung© complianceJones & andBartlett some areas Learning, have better LLC and some in the anterior© Jones portion of& theBartlett thorax. Learning,With supine posi-LLC haveNOT worse FOR pulmonary SALE mechanics. OR DISTRIBUTION A prolonged TI tioning, theNOT dependent FOR portions SALE of OR the DISTRIBUTIONlung lie posterior may improve gas distribution and Pao2, although PC- to the heart, while nondependent portions of the lung IRV has not been shown to be effective in all cases of lie close to the heart. With prone positioning, the de- ARDS. Flow, pressure, and volume–time curves for pendent portions of the lung are adjacent to the heart time-triggered and patient-triggered volume ventilation and the nondependent portion of the lung lies away © Jones & (VC-CMV)Bartlett Learning,are illustrated LLC in Figure 3-18. © Jonesfrom the& Bartlettheart. When Learning, compared, thereLLC is somewhat NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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© Jones0 & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 024613578 9110 1112 3 14 NOT FOR SALE OR DISTRIBUTION Time (seconds) NOT FOR SALE OR DISTRIBUTION (B) Figure 3-18 Flow, Pressure, and Volume–Time Curves for Time-Triggered and Patient-Triggered Volume Ventilation (VC-CMV). (A) Time-triggered volume ventilation (VC-CMV), sometimes referred to as controlled ventilation. (B) Patient-triggered volume ventilation (VC-CMV), sometimes referred to as assist-control ventilation. © Jones & FromBartlett Waugh JB, Deshpande Learning, VM, Brown MK, LLC Harwood R. Rapid Interpretation of Ventilator Waveforms© Jones. 2nd ed. Upper& Bartlett Saddle River, NJ: Learning, Prentice Hall; 2006. LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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© Jones & Bartlett Learning, LLC © Joneswas achieved & Bartlett by allowing Learning, a window LLC of time to open dur- NOTing FOR which SALE the patient OR DISTRIBUTIONcould trigger a mandatory breath. NOT FOR SALE OR DISTRIBUTION If the patient did not trigger a breath during the time window provided, the ventilator would then provide a time-triggered mandatory breath. SIMV helped avoid breath stacking and patient–ventilator asynchrony. © Jones & Bartlett Learning, LLCToday, most modern ventilators© Jones provide SIMV.& Bartlett While Learning, LLC (A) Supine with no heart (B) Prone with no heart NOT FOR SALE OR DISTRIBUTIONthe term SIMV is common use,NOT the FORrecommended SALE no-OR DISTRIBUTION menclature is to use IMV for both time-triggered “traditional” IMV and for SIMV. Most modern critical care ventilators offer IMV/SIMV as a mode choice, which can be volume controlled or pressure controlled and © Jones & Bartlett Learning, LLC used with (or© without)Jones CPAP& Bartlett and/or PSV.Learning, LLC NOT FOR SALE OR DISTRIBUTION With volume-controlledNOT FOR SALE IMV or OR V-SIMV, DISTRIBUTION the clinician sets a tidal volume and rate. This guarantees a minimum minute volume to the patient. The patient (C) Supine with heart (D) Prone with heart can spontaneously breathe between the machine delivered breaths, and these spontaneous breaths may be © Jones & Bartlett Learning,Poor LLCly ventilated © Jonespressure & supportedBartlett andLearning, provided withLLC (or without) an Well ventilated NOT FOR SALE OR DISTRIBUTION NOTelevated FOR SALE baseline OR (i.e., DISTRIBUTION with or without PEEP/CPAP). No gas exchange If the patient begins to inspire spontaneously just prior to a time-cycled machine breath, the ventilator Figure 3-19 Graphic Representation of Anticipated Aeration of will treat that breath as an assisted, patient-triggered, Lung Units in ARDS Patients in the Supine (A, C) and Prone (B, D) Positions. machine-delivered mandatory breath with a preset From Henderson WR Griesdale DE© Dominelli Jones P, Ronco &R Does Bartlett prone positioning Learning, improve LLCtidal volume. © Jones & Bartlett Learning, LLC oxygenation and reduce mortality in patients with acute respiratory distress syndrome? With IMV, initial ventilator settings are usually set to Can Respir J. 2014;21(4):213–215.NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION provide full ventilatory support (e.g., mandatory rate of 10 to 12 breaths/min with an adequate set tidal volume). better ventilation and oxygenation if the nondependent Based on the patient’s response, the number of manda- portion of the lung does not contain the heart (i.e., tory breaths can be then reduced, to provide partial prone position). Schematic diagrams of the chest com- ventilatory support, whereby the patient must contrib- partment© Jones while & prone Bartlett and supine Learning, (Figure 3-19 LLC) show © Jones & Bartlett Learning, LLC ute a sufficient level of his or her required ventilation in decreasedNOT FOR aeration SALE in the OR gravity DISTRIBUTION dependent regions.20 NOT FOR SALE OR DISTRIBUTION the form of spontaneous breathing. The mandatory rate Intermittent Mandatory Ventilation could then be incrementally reduced to “wean” the patient from the ventilator. It must be noted, however, that Intermittent mandatory ventilation (IMV) was intro- weaning is not required for most patients and the pre- © Jones & ducedBartlett in the Learning, early 1970s andLLC was advanced as a superior© Jonesferred &method Bartlett for ventilator Learning, discontinuance LLC is generally mode of ventilation for several reasons (e.g., reduced the spontaneous breathing trial (SBT). NOT FOR SALEmean airway OR DISTRIBUTIONpressures, improved venous return, NOT FORCare SALEmust be ORtaken DISTRIBUTION with V-SIMV to properly set the maintaining ventilatory muscle function, and rapid high-pressure alarm (and limits) to reduce the risk of ventilator weaning). Early forms of IMV combined a pulmonary barotrauma and to set other alarms to detect time-triggered mandatory respiratory rate with a system hypoventilation, particularly when using low mandatory to allow the patient to© breath Jones spontaneously & Bartlett in Learning, between LLCmachine rates. Hypoventilation© Jonesmay occur & if Bartlett sponta- Learning, LLC mandatory breaths. Spontaneous breaths generally neous minute volumes decrease for any reason (e.g., included a small amountNOT of FOR“physiologic SALE PEEP” OR (e.g.,DISTRIBUTION sedative or narcotic administration,NOT FORventilatory SALE muscle OR DISTRIBUTION 3 to 5 cm H2O) provided in the form of CPAP. Prior to fatigue, or CNS problems). being “synchronized” (SIMV), the patient could take a With pressure-controlled IMV or P-SIMV, the clini- spontaneous inspiratory breath at any point in the cycle, cian sets an inspiratory pressure and respiratory rate. although© Jones the ventilator & Bartlett was setLearning, by time to deliverLLC its me- Mandatory© breath Jones tidal & volume Bartlett is determined Learning, by the LLC chanicalNOT breath.FOR SALEThat meant OR theDISTRIBUTION patient could be inspir- inspiratory NOTpressure, FOR inspiratory SALE timeOR (TDISTRIBUTIONI), and the pa- ing or exhaling and the machine would still cycle into tient’s lung mechanics (e.g., compliance and resistance). inspiration resulting in patient–ventilator asynchrony With P-SIMV the patient can breathe spontaneously and increased WOB. Breath stacking could occur when between mandatory breaths and these spontaneous a mandatory breath was stacked on top of a spontane- breaths may be pressure supported (e.g., PSV) with or © Jones & ousBartlett breath. Learning,The patient couldLLC also be trying to exhale © Joneswithout & PEEP/CPAP.Bartlett Learning, Properly adjusted LLC alarm settings NOT FOR SALEwhile the OR machine DISTRIBUTION was forcing an inspiration. NOTare FOR important SALE as OR the mandatoryDISTRIBUTION breath tidal volume and Synchronized intermittent mandatory ventilation resultant minute ventilation may vary with changes in (SIMV) was introduced to avoid these problems. This lung mechanics (Figure 3-20).

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0 © Jones02468 & Bartlett1357 Learning, LLC © 91Jones10 & Bartlett1112 Learning,3 14 LLC Time (seconds) (B)NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Figure 3-20 Graphic Display of the Differences Between VC-SIMV (A) and PC-SIMV (B). In A, the tidal volume is set by the respiratory therapist and does not change resulting in pressure variations with changes in lung mechanics (as noted in the second machine-delivered breath). In B, the

pressure is set by the respiratory therapist and VT will vary with changes in lung mechanics. From Tobin MJ. Principles and Practice of Mechanical Ventilation. 2nd ed. New York, NY: McGraw-Hill; 2006: 68−69. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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© Jones &Positive Bartlett End-Expiratory Learning, LLC Pressure © Jonesat the initiation& Bartlett of the Learning, mandatory ventilatorLLC breath, followed by a shift in the curve as compliance improves. NOT FOR SALEPositive ORend-expiratory DISTRIBUTION pressure (PEEP) is intended to NOT FOR SALE OR DISTRIBUTION splint the airways open, improve the distribution of gas, The point at which the curve shifts is known as the and prevent alveolar collapse. PEEP increases functional lower inflection point (LIP). Using this method, PEEP is residual capacity (FRC) and may improve oxygenation set 2 cm H2O above the LIP. It must be noted that not in patients with acute restrictive pulmonary disease all ARDS patients exhibit an LIP. (e.g., ARDS, pneumonia,© Jones and atelectasis). & Bartlett PEEP Learning, provides LLC © Jones & Bartlett Learning, LLC Lung Recruitment Maneuvers and PEEP an elevated baseline NOTpressure FOR during SALE expiration. OR DISTRIBUTIONEndo- NOT FOR SALE OR DISTRIBUTION tracheal intubation can result in a small reduction in Lung recruitment maneuvers are sometimes applied in patients’ FRC due to the loss of normal glottic function. patients with ARDS to improve V˙/Q˙ and reduce shunt- A small amount (3 to 5 cm H2O) of “physiologic PEEP” ing. One method involves the use of pressure-control has been suggested for most patients, to balance the loss ventilation in which PEEP is set in the range of 20 to of “natural© Jones PEEP” & Bartlettfollowing endotracheal Learning, intubation. LLC 25 cm H2O ©and Jones the pressure-control & Bartlett levelLearning, is set about LLC PEEPNOT may FOR reduce SALE the incidence OR DISTRIBUTION of ventilator-associated 15 cm H2O NOTabove PEEPFOR for SALE a period OR of DISTRIBUTION2 to 3 minutes. pneumonia and prevent the development of hypoxemia. This is followed by a decremental PEEP study to PEEP applied intentionally for therapeutic purposes identify the PEEP level at which compliance is at its is known as extrinsic PEEP or applied PEEP. Uninten- highest value. tional PEEP due to incomplete airway emptying during There are differences in mechanical ventilators when © Jones & expirationBartlett isLearning, known as intrinsic LLC PEEP, “inadvertent © Jonessetting & PEEP Bartlett during Learning, pressure-control LLC ventilation and NOT FOR SALEPEEP,” “accidental OR DISTRIBUTION PEEP,” “ghost PEEP,” or “autoPEEP.” NOTthe FOR manuals SALE for eachOR ventilatorDISTRIBUTION should be consulted Intrinsic PEEP causes pulmonary overinflation and can prior to initiation of a pressure-controlled mode. PEEP cause difficulty for the patient in triggering the ventila- may contribute to pulmonary barotrauma and alveolar tor. Steps to correct for autoPEEP should be taken, and overdistention resulting in ventilator-associated lung may include using smaller tidal volumes, decreasing injury. To avoid this, Pplateau should be kept ≤ 30 cm inspiratory time, increasing© Jones expiratory & Bartlett time, reducing Learning, LLCH2O. It should be noted that ©use Jones of PEEP &in Bartlettseverely Learning, LLC mandatory respiratoryNOT rate, FOR and the SALE application OR DISTRIBUTIONof a hypoxemic patients with unilateralNOT orFOR focal SALE lung disease OR DISTRIBUTION small amount of extrinsic PEEP, usually less than the (focal pneumonia) may be ineffective. PEEP should also measured autoPEEP value (e.g., 50% of autoPEEP level). be used very cautiously in patients with obstructive lung The use of extrinsic PEEP to balance autoPEEP probably disease, hemodynamic instability, or increased ICP. should be limited to patients that have trouble trigger- Fick’s law applies to diffusion of gas across the alveo- ing© the Jones ventilator. & Bartlett Learning, LLC lar capillary© (AC) Jones membrane, & Bartlett which isLearning, determined byLLC NOTPEEP levelsFOR in SALE the range OR of 5DISTRIBUTION to 20 cm H2O are often Pao2 and theNOT AC surface FOR area;SALE PEEP OR increases DISTRIBUTION the sur- used to improve oxygenation and reduce the harmful face area for gas exchange. Respiratory care clinicians effects of cyclic alveolar collapse and re-inflation that use combinations of Fio2 and PEEP to achieve target can occur with ARDS in the absence of PEEP. Improve- Pao2 and Sao2 values at a “safe” Fio2 (generally ≤ 0.50 ment in patients’ Pao2/Fio2 ratio with PEEP is associ- to 0.60). PEEP contributes directly to the mean airway © Jones & atedBartlett with decreased Learning, mortality LLC in ARDS. Optimal PEEP © Jonespressure, & Bartlettand when increasesLearning, in PEEP LLC are considered, NOT FOR SALElevels have OR not DISTRIBUTION been definitively identified, and many NOTthe FOR effects SALE on venous OR DISTRIBUTIONreturn and cardiac output should methods of applying PEEP have been advocated. These be considered. When adjusting Fio2 and PEEP, there include using the least PEEP necessary to achieve an ac- may be necessary tradeoffs between the hazards of 2O ceptable Fio2 (aka minimal PEEP), titrating PEEP based toxicity versus the possibility of ventilator-associated on oxygen delivery, compliance-titrated PEEP, and use lung injury due to higher PEEP. Through research of pressure–volume ©curves Jones to set & the Bartlett optimum Learning, PEEP LLCconducted and reported in the© ARDSNetJones & trials, Bartlett it was Learning, LLC level. The ARDS ClinicalNOT NetworkFOR SALE suggests OR use DISTRIBUTIONof an noted that more severe ARDSNOT patients FOR may SALE benefit OR from DISTRIBUTION Fio2–PEEP table to adjust PEEP levels. more aggressive PEEP levels (12 to 24 cm H2O) while Viewing the patient’s pressure–volume curves during mild cases of ARDS generally show improved oxygen- mechanical ventilation can be helpful in the determi- ation with lower PEEP levels. Protocols have reduced nation of an appropriate PEEP setting. When zero or ventilator-induced lung injury and problems associated sub-therapeutic© Jones & PEEP Bartlett is applied Learning, in patients LLC with ARDS, with pulmonary© Jones O2 toxicity. & Bartlett Learning, LLC theNOT small FORairways SALE may collapse OR DISTRIBUTION during expiration and To summarize,NOT FORPEEP canSALE often OR be very DISTRIBUTION useful in re-inflate during inspiration. Each inspired breath may improving oxygenation in patients with acute, se- result in shearing forces or wall stress. This could lead vere restrictive lung disease (e.g., ARDS). PEEP in- to an increased inflammatory response and worsen- creases mean airway and intrathoracic pressure and ing of overall lung condition. With subtherapeutic may promote the development of barotrauma and © Jones & PEEP,Bartlett a slow Learning, flow (e.g., inspiratory LLC flow < 10 L/min) © Jonesventilator-associated & Bartlett Learning, lung injury (VALI) LLC, and reduce NOT FOR SALEpressure–volume OR DISTRIBUTION curve may indicate low compliance NOTvenous FOR return,SALE cardiac OR DISTRIBUTION output, and systemic blood

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© Jones &pressure. Bartlett PEEP Learning, can increase LLC ICP, and this should be © JonesCPAP &should Bartlett be used Learning, cautiously in LLC patients with ob- kept in mind when treating patients with increased ICPNOT structive FOR SALE lung disease OR DISTRIBUTIONand in those with hemodynamic NOT FOR SALE(e.g., head OR trauma). DISTRIBUTION instability or elevated ICP.

Continuous Positive Airway Pressure CPAP and Obstructive Sleep Apnea Continuous positive airway pressure (CPAP) describes Obstructive sleep apnea (OSA) is defined as the ces- spontaneous breathing© Jonesat an elevated & Bartlett baseline Learning,pres- LLCsation of airflow for ≥ 10 seconds© Jones with evidence & Bartlett of Learning, LLC sure. Like PEEP, CPAPNOT increases FOR mean SALE airway OR pressure DISTRIBUTION sustained inspiratory effort. NOTNoninvasive FOR SALECPAP deliv- OR DISTRIBUTION and mean intrathoracic pressure and FRC. In the ICU, ered by oral or nasal mask at pressures in the range of CPAP may be provided through the ventilator, or inde- 4 to 20 cm H2O is the preferred treatment for OSA. pendently using a high-flow, blended and humidified In this range, CPAP splints the soft tissue of the up- gas source and a PEEP valve. Acute care uses of CPAP per airway and prevents collapse, airway obstruction, include© Jones improving & Bartlett oxygenation Learning, in patients LLCwith respira- and apnea. CPAP© Jones is also & indicated Bartlett for Learning,the treatment LLC toryNOT failure, FOR prevention SALE of OR postoperative DISTRIBUTION atelectasis, and of clinically NOTsignificant FOR obstructive SALE OR hypopneas. DISTRIBUTION For treatment of cardiogenic pulmonary edema. A number OSA, the CPAP pressure should be titrated in the of small, portable CPAP machines have also been de- sleep laboratory for any patient with multiple comor- veloped for in-home use to treat obstructive sleep apnea bidities, significant cardiac history, or morbid obesity. (OSA); these units are sometimes employed in the acute Patients with high BMI may require very high levels © Jones & careBartlett setting Learning,for patients with LLC OSA. © Jonesof CPAP & toBartlett control OSA.Learning, If CPAP LLCof 20 cm H2O fails NOT FOR SALEWith OR CPAP, DISTRIBUTION the patient both initiates and termi- NOTto FOR adequately SALE control OR DISTRIBUTIONOSA, BiPAP may be employed. nates an inspiration. Put another way, CPAP provides BiPAP combines inspiratory positive airway and patient-triggered and patient-cycled breaths. CPAP expiratory positive airway pressure (EPAP), which is can be provided as a standalone mode (i.e., continuous titrated to a maximum setting of 30/25 cm H2O spontaneous ventilation [CSV]) or in combination with (IPAP/EPAP). Mask leak, patient intolerance of pres- pressure support. CPAP© Jones may also & be Bartlett used with Learning, IMV. LLCsure, and aerophagia (air swallowing)© Jones are &problems Bartlett as- Learning, LLC CPAP may be providedNOT by maskFOR or SALE via a cuffed OR DISTRIBUTIONendotra- sociated with high positive airwayNOT pressures. FOR SALE OR DISTRIBUTION cheal or tracheostomy tube. In addition to CPAP, other strategies for OSA man- With CPAP, the breathing circuit pressure is elevated agement include sleeping with the head of the bed el- during inspiration and expiration. Thus, CPAP pro- evated, dental appliances, and weight loss (e.g., bariatric vides a form of inspiratory pressure augmentation that surgery). Other techniques that have been employed may© reduce Jones the & inspiratory Bartlett WOB Learning, during spontaneous LLC with varying© degrees Jones of &success Bartlett include Learning, autotitrating LLC breathing.NOT FOR This SALEmay be helpfulOR DISTRIBUTION in patients undergoing CPAP or autotitratingNOT FOR positive SALE airway OR pressureDISTRIBUTION (APAP) spontaneous breathing trials (SBTs) leading to extu- and adaptive servo-ventilation (ASV) with CPAP. bation. Like PEEP, CPAP’s elevated expiratory pres- Autotitrating CPAP varies the airway pressure during sure increases FRC and the lung surface area for gas the night based on specific algorithms. ASV is a closed- exchange. Thus, CPAP may improve oxygenation and loop form of ventilation that uses breath-to-breath anal- © Jones & helpBartlett prevent Learning, alveolar collapse LLC and atelectasis. As noted,© Jonesysis to &target Bartlett a desired Learning, minute volume LLC and minimize NOT FOR SALECPAP increases OR DISTRIBUTION mean airway pressure and intrathoracicNOT WOB. FOR ASV SALE may ORbe useful DISTRIBUTION in patients with abnormal pressure; excessive levels may decrease venous return, breathing patterns and complex sleep apnea. The major decrease cardiac output, and decrease blood pressure. problem associated with CPAP and OSA treatment is Figure 3-21 compares pressure–time curves for base- patient compliance. Other complications associated line spontaneous breathing and CPAP. As with PEEP, with CPAP are highlighted in Box 3-8. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC + NOT FOR SALE OR DISTRIBUTIONRecruitment Maneuvers withNOT CPAP FOR SALE OR DISTRIBUTION CPAP O) 2 Baseline = +5 Very high levels of CPAP for brief periods of time (e.g., +5 40 cm H2O for 40 seconds) have been suggested as a 0 part of recruitment maneuvers to open collapsed alveoli © Jones & Bartlett Learning,Spontaneous LLC breathing in patients with© Jones ARDS. &Such Bartlett recruitment Learning, maneuvers LLC essure (cm H essure Baseline = 0 should not be routinely employed, although some pa- NOTPr – FOR SALE OR DISTRIBUTION tients may benefit.NOT FOR SALE OR DISTRIBUTION Time Noninvasive Ventilation Figure 3-21 Comparison of the Pressure–Time Curves for Spontaneous Breathing and CPAP. Spontaneous breathing is A commonly employed version of noninvasive venti- © Jones & measuredBartlett at an Learning, atmospheric baseline LLC pressure (0 cm H2O) and CPAP© Joneslation &(NIV) Bartlett uses bilevel Learning, airway pressure LLC (BiPAP) to NOT FOR SALEis measured OR at anDISTRIBUTION elevated baseline pressure of +5 cm H2O. NOTprovide FOR SALEventilatory OR support. DISTRIBUTION BiPAP combines IPAP with

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© Jones & Bartlett Learning, LLC © Jonesnot been & Bartlettshown to be Learning, helpful for patientsLLC with acute hy- BOX 3-8 Complications of CPAP Therapy poxemic respiratory failure (e.g., ARDS). NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION in OSA Pressure-Support Ventilation 1. Subtherapeutic pressures resulting in continued OSA, fatigue, and persistence of excessive day- Pressure-support ventilation (PSV) provides for time sleepiness (EDS) patient-triggered, pressure-limited, flow-cycled venti- © Jones & Bartlett Learning, LLClation. PSV may be further described© Jones as spontaneous& Bartlett Learning, LLC yyTry: Sleep labNOT titration FOR study SALE or autoPAP OR DISTRIBUTION trial breathing with inspiratory pressureNOT FORaugmentation; SALE OR DISTRIBUTION (adjust range clinically). expiration may include the addition of an elevated 2. Pressure intolerance baseline (i.e., PEEP/CPAP). PSV allows the patient to achieve a given spontaneous tidal volume with less yyTry: CPAP desensitization, add Cflex, switch to effort. PSV overcomes the resistance to ventilation © JonesBiPAP, in-lab& Bartlett titration, Learning, verify mask seal,LLC or © Jones & Bartlett Learning, LLC autoPAP trial (adjust range clinically). caused by ventilator circuits and artificial airways. PSV NOT FOR SALE OR DISTRIBUTION may enhanceNOT weaning. FOR PSV SALE also allows OR DISTRIBUTION the clinician to 3. Aerophagia (air swallowing) adjust the ventilatory workload of the patient. PSV may yyTry: Decreasing CPAP pressure, abdominal be used as a standalone mode or in conjunction with gas relievers, or autoPAP trial (adjust range IMV/SIMV. clinically). Modest levels of pressure support (e.g., 5 to 15 cm © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 4. Dry mouth after CPAP use H2O) can be used to overcome the imposed WOB due NOT FOR SALE OR DISTRIBUTION NOTto FOR endotracheal SALE orOR tracheostomy DISTRIBUTION tubes. Higher levels of yyTry: Chin strap, full face mask, or consider PSV (e.g., 15 to 25 cm H2O) further reduce the patient’s weight loss, positional therapy, oral appli- WOB. Low levels of PSV (5 to 8 cm H2O) are often em- ances or surgical alternatives. ployed in conjunction with CPAP during spontaneous 5. Asynchrony breathing trials (SBTs) to evaluate readiness for ventila- © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC yyVerify pressure in BiPAP; check inspiratory rise tor discontinuance and extubation. time and inspiratoryNOT FOR time. SALE OR DISTRIBUTIONWith PSV, patients can controlNOT their FOR respiratory SALE OR DISTRIBUTION rate and inspiratory flows, times, and volumes. As a Anxiety or vanity 6. patient-triggered mode, pressure support should not be yyTry: Education or sedatives or consider alter- used in patients with unstable ventilatory drives or pe- ˙ native forms of treatment. riods of apnea. High and low VE alarms should be set to © Jones & Bartlett Learning, LLC © Joneshyperventilation & Bartlett Learning, LLC AutoPAP, automatic positive airway pressure; BiPAP, bilevel help detect hypo- or . positiveNOT airway FOR pressure; SALE CPAP, OR continuous DISTRIBUTION positive airway Choice ofNOT pressure-support FOR SALE pressure OR DISTRIBUTION level depends pressure; EDS, excessive daytime sleepiness; OSA, obstructive on the specific goal. Common goals include: sleep apnea. ■■ Reducing or eliminating the imposed work of breathing (WOBI) associated with spontaneous © Jones & Bartlett Learning, LLC © Jones breaths& Bartlett in between Learning, mandatory LLC breaths in the IMV/SIMV mode. PSV values needed to eliminate NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION EPAP. With BiPAP, the patient typically initiates and WOBI will vary depending on the patient’s venti- terminates inspiration; however, inspiratory pressure latory pattern and endotracheal or tracheostomy augmentation is provided (i.e., IPAP) and expiratory tube diameter but are generally the range of 5 to pressure maintains an elevated baseline (i.e., EPAP). 15 cm H2O. ■■ BiPAP is typically ©applied Jones using & anBartlett oral or nasal Learning, LLC Reducing or eliminating© the Jones imposed & workBartlett of Learning, LLC mask. EPAP is initially set in the range of 5 to 10 cm breathing (WOBI) associated with spontane- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION H2O and titrated to achieve acceptable oxygenation ous breaths during a spontaneous breathing trial while minimizing patient discomfort. IPAP is set to (SBT). Here, PSV values needed will also vary achieve an inspiratory pressure of 5 to 15 cm H2O above depending on the patient’s ventilatory pattern and EPAP and titrated to achieve adequate ventilation and endotracheal/tracheostomy tube diameter. Cur- reduced© Jones WOB. & Bartlett Learning, LLC rent guidelines© Jones suggest & Bartlett initiating Learning, PSV at 5 to 8LLC cm NOTNIV may FOR be especially SALE OR useful DISTRIBUTION in patients with acute H2O duringNOT FORSBTs. SALE OR DISTRIBUTION respiratory failure due to COPD exacerbation to reduce ■■ Providing a relatively high level of ventilatory the need for endotracheal intubation, decrease length support that may improve patient–ventilator syn- of hospital stay, and decrease mortality. NIV is also chrony and comfort and reduce the WOB. PSV indicated in patients at high risk for extubation failure, used in this fashion is adjusted to achieve an ad- © Jones & andBartlett extubation Learning, to NIV has LLC been recommended in this © Jones equate& Bartlett tidal volume Learning, (4 to 8 mL/kg LLC IBW) usually at ≤ NOT FOR SALEgroup. NIV OR may DISTRIBUTION be useful in other acute and chronic NOT FORa reasonableSALE OR spontaneous DISTRIBUTION respiratory rate (f 25 conditions, as further described in Chapter 10. NIV has breaths/min). To vary the tidal volume received by

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© Jones & Bartlettthe patient, Learning, the respiratory LLC care clinician simply © JonesIt is & important Bartlett in Learning,APRV to control LLC exhalation to increases or decreases the pressure-support level inspiration cycling to prevent derecruitment of alveoli NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION provided and monitors the resultant expired tidal during the expiratory phase. Tlow may be as short as volumes. 0.3 sec with restrictive lung disease or as long as 1.5 sec ■■ Providing an alternative method for patient wean- with obstructive lung disease.23 Weaning from APRV ing from mechanical ventilatory support. PSV can be accomplished when Phigh is reduced to 10 cm < generally is initiated© Jones at a relatively & Bartlett high level Learning, for LLCH2O, Thigh at 12 to 15 seconds,© and Jones Fio2 & 50%. Bartlett The Learning, LLC these patients. NOTWhen FORthe patient SALE meets OR certain DISTRIBUTION clinician can switch to CPAPNOT 10 cm FORH2O with SALE PSV OR DISTRIBUTION readiness criteria, PSV is reduced 2 to 4 cm H2O 5 to 10 cm H2O and wean as tolerated to extubation in a stepwise fashion. Each reduction in PSV level (Clinical Focus 3-4). is followed by careful assessment for signs of dis- In a 2016 paper on the pros and cons of APRV, tress to assess tolerance. PSV continues to be de- Mireles-Cabodevila and Kacmarek make the point that © creased,Jones as& tolerated. Bartlett If Learning,signs of intolerance LLC occur, most of the ©positive Jones aspects & Bartlett of APRV Learning,come from animal LLC NOTPSV FOR is returned SALE to itsOR previous DISTRIBUTION level. studies. TheirNOT summary FOR suggestsSALE ORno clear DISTRIBUTION advantage of APRV over conventional mechanical ventilation with Figure 3-15 illustrates flow, pressure, and volume lung protective strategies employed.24 In a recent study waveforms typically seen with PSV. of 138 patients with ARDS, Zhou et al. found that com- Airway Pressure-Release Ventilation pared to lung protective ventilation, APRV patients © Jones & Bartlett Learning, LLC © Joneshad a reduced& Bartlett mortality Learning, rate, reduced LLC ventilator days, Airway pressure-release ventilation (APRV) is an- 25 NOT FOR SALE OR DISTRIBUTION NOTand FOR reduced SALE number OR DISTRIBUTIONof days in the ICU. A follow-up other mode used for spontaneously breathing patients review of this work did note some of the potential (Figure 3-22). APRV provides two levels of CPAP that limitations of their study including being unblinded, are time triggered and time cycled. Patients may breathe levels of sedation used, and increased comorbidity in spontaneously at both levels. The high-pressure set- the conventional mechanical ventilation/low VT control 26 ting may last several ©seconds Jones and & is Bartlett intended as Learning, an LLCgroup. APRV is available on© the Jones Getinge & Servo-i Bartlett and Learning, LLC airway/alveolar recruitmentNOT FOR technique SALE like OR other DISTRIBUTION modes Servo-u; Dräger Evita InfinityNOT V500, FOR Babylog SALE VN500; OR DISTRIBUTION of inverse-ratio ventilation (i.e., PC-IRV). As noted, Hamilton G5, C1, C3, MR1; T1, GE Carescape R 860; the patient may spontaneously breathe while at the and Vyaire AVEA and VELA. high-pressure setting. The machine time cycles to the low-pressure setting to aid in CO elimination, lower 2 Automatic Tube Compensation mean© Jonesairway pressures, & Bartlett and reduceLearning, the risk LLC of cardio- © Jones & Bartlett Learning, LLC vascularNOT compromise. FOR SALE The OR patient DISTRIBUTION may also spontane- Automatic tubeNOT compensation FOR SALE (ATC) OR isDISTRIBUTION a variable form ously breathe in the low-pressure setting. of pressure support used as an adjunct to other modes The intent of this mode is ventilation and oxygenation of ventilation and designed to reduce the WOB associ- in patients with regional lung compliance heterogene- ated with endotracheal tube resistance. The difference ity and severe oxygenation problems (e.g., ARDS). The is the within breath variability to adjust support in rela- © Jones & ventilatorBartlett controls Learning, and settings LLC used to achieve APRV © Jonestion to & the Bartlett patient’s Learning,inspiratory flow LLC rate. The improved vary among different ventilators. Since there is a high- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION pressure set (Phigh) that is time based, the ventilator may call for a Thigh and Tlow to be set (Figure 3-23). The inspiratory phase may last 3 to 6 seconds and the expiratory T phase (Tlow) may last 0.5 to 0.8 seconds. The high pres- high sure (Pplateau or Phigh) should be ≤ 30 cm H2O. The pres- ATC © Jones & Bartlett Learning, LLCPhigh © Jones & Bartlett Learning, LLC sure at Tlow may be zero (i.e., atmospheric) or elevated.

NOT FOR SALE OR DISTRIBUTIONessure NOT FORP meanSALE OR DISTRIBUTION

Pr Plow

+ Spontaneous Tlow CPAP breaths level 1 © pressure Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC

ay CPAP NOT0 FOR SALE OR DISTRIBUTIONlevel 2 NOT FOR SALE OR DISTRIBUTION

Airw – Time Fl ow

Figure 3-22 Airway Pressure-Release Ventilation (APRV). Note that patients may breathe spontaneously at either CPAP level during APRV. © Jones & FromBartlett Pilbeam SP, CairoLearning, JM, Barraza P. Special LLC techniques in ventilatory support. In: Cairo © JonesFigure & 3-23 Bartlett Airway Pressure-Release Learning, Ventilation. LLC JM (ed). Pilbeam’s Mechanical Ventilation. 5th ed. St. Louis, MO: Mosby; 2012: Figure 23-1. From Blosser S. Airway pressure release ventilation (APRV) management. APRV Final Exam. NOT FOR SALEAvailable at https://thoracickey.com/special-techniques-in-ventilatory-support/.OR DISTRIBUTION NOTAvailable FOR at https://www.pdffiller.com/101286566-aprvpdf-APRV-final-from-Sandy-Blosser-.SALE OR DISTRIBUTION

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© Jones & Bartlett Learning, LLC © Jones & BartlettCLINICAL Learning, FOCUS 3-4 LLC ARDS NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Your patient is a 72-year-old man 7 days post mo- 2. Yes: His lung, heart, kidney, and possibly CNS func- tor vehicle accident with chest wall trauma. He has tion appear to be affected. been on mechanical ventilation with current settings: 3. He is retaining fluid as evidenced by the eightw gain PC-SIMV, Fio2 of 55%, PIP 32 cm H2O, RR 16 bpm, PEEP and decreasing urine output. +8 cm H O, and PS© + Jones8 cm H O.& HisBartlett machine Learning, delivered LLC © Jones & Bartlett Learning, LLC 2 2 4. Airway pressure-release ventilation. VT has been 420 mLNOT and heFOR is breathing SALE spontaneouslyOR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION APRV is initiated with the following settings: Fio2 with RRs of 14 bpm and spontaneous VT of 220 mL. He 55%, Phigh 28 cm H2O, Plow 4 cm H2O, Thigh 5 sec, and has a 90 pack-year history smoking and two right-side Tlow 1.0 sec. Following APRV initiation, ABGs were: rib fractures (4th and 5th). The patient has a low-grade pH 7.35, Paco2 54 mmHg, Pao2 67 mmHg, and fever with an elevated white cell count, although the − © Jones & Bartlett Learning, LLC HCO3 29 mEq/L.© Jones & Bartlett Learning, LLC eosinophilsNOT FOR are SALE within normalOR DISTRIBUTION limits (WNL). Ausculta- NOT FOR SALE OR DISTRIBUTION tory findings are bilateral inspiratory crackles (rales). Questions: The patient’s urine output has been dropping over the 1. Classify ABGs while on PC-SIMV and APRV. past 2 days and Lasix has been ordered. Blood urea 2. What are the considerations for choosing the high nitrogen (BUN) and creatinine are becoming elevated. and low APRV pressures? © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC His weight has gone up 4 lbs since admission. His 3. When weaning from APRV, what mode can be used NOT FOR SALEchest ORx-ray DISTRIBUTION appears consolidated bilaterally with veryNOT FORwhen SALEPhigh ≤ 10 OR cm DISTRIBUTIONH2O? little aeration noted. His BP is 90/58 and HR is 105 4. Does the patient seem to be doing better with the bpm. He can follow most oral commands. The most change to APRV? recent ABG findings are pH 7.29, Paco2 64 mmHg, Pao2 − Answers: 47 mmHg, and HCO©3 Jones 30 mEq/L. & ABartlett decision isLearning, made to LLC © Jones & Bartlett Learning, LLC switch to APRV. 1. PC-SIMV: Partially compensated respiratory acido- NOT FOR SALE OR DISTRIBUTIONsis with moderate hypoxemia.NOT APRV: FOR Compensated SALE OR DISTRIBUTION Questions: respiratory acidosis with mild hypoxemia. What is this patient’s Pao /Fio ratio? Is this consis- 1. 2 2 2. A slow-flow pressure−volume curve may be tent with a diagnosis of acute respiratory distress obtained and the lower inflection point (LIP) syndrome (ARDS)? © Jones & Bartlett Learning, LLC pressure observed.© Jones P low& shouldBartlett then Learning, be adjusted LLC Is this scenario consistent with multiorgan 2.NOT FOR SALE OR DISTRIBUTION to be 2 cmNOT H2O aboveFOR the SALE LIP. The OR high DISTRIBUTION inflection dysfunction? point should also be observed and Phigh should 3. Why is this patient gaining weight while an be below this point. As a general rule, Phigh inpatient? should be ≤ 30 cm H2O and roughly equal to the 4. What does the acronym APRV stand for? Pplateau obtained during conventional mechanical © Jones & Bartlett Learning, LLC © Jonesventilation. & Bartlett Learning, LLC NOT FOR SALEAnswers: OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 3. CPAP 1. The Pao2/Fio2 ratio is 82. Ratios of arterial O2 Yes partial pressures to O2 concentrations < 300 4. but > 200, ≤ 200 but > 100, and ≤ 100 are consistent with mild, moderate, and severe ARDS respectively.© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

control of WOB, when comparing ATC to PSV, is more clinical goals (e.g., resting the diaphragm or allowing 27 evident© Jones in patients & Bartlett with high Learning, minute ventilation LLC or some patient© contributionJones & Bartlett to WOB) andLearning, clinician. LLC increasedNOT FOR respiratory SALE drive. OR The DISTRIBUTION advantage of ATC is Although intendedNOT FOR to reduce SALE the ORWOB DISTRIBUTION in patients, inspiratory flow control using intratracheal pressure one study comparing weaning using ATC vs. T-piece as the measured variable. Support and flow are added showed no significant difference in variables such as during inspiration when spontaneous inspiratory acti- PETCO2, Sao2, RR, MAP, or HR. There was also no dif- vation alters the pressure difference across the endotra- ference in the reintubation rates comparing ATC and 28 © Jones & chealBartlett tube (Learning,Figure 3-24). LLCWhen using ATC, variables © JonesT-piece & trials. Bartlett Automatic Learning, tube compensation LLC is avail- NOT FOR SALEare entered OR into DISTRIBUTION the ventilator such as ET tube diameterNOT able FOR on theSALE Hamilton OR DISTRIBUTIONG5, Covidien PB 840 and PB 980, and the percentage of support as determined by the and Dräger Evita XL.

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PSV 5 cm H O © Jones & Bartlett Learning, LLC 2 © Jones & Bartlett Learning, LLC 10 BOX 3-9 Equation of Motion NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION The equation of motion provides a mathematical model of patient–ventilator interaction, where:

O) 5 2 Pvent (t) = [E × V(t)] + [R × V˙ (t)] © Jones & Bartlett Learning, LLCThe equation of motion describes© Jones the pressure& Bartlett Learning, LLC 0 NOT FOR SALE OR DISTRIBUTIONrequired to overcome the elasticNOT andFOR resistive SALE OR DISTRIBUTION

essure (cm H essure Pcirc properties (or loads) of the lung. The elastic forces Pr Ptrach are proportional to tidal volume and the resistive –5 PEEP forces are proportional to airflow. In the presence of both ventilatory work provided by the ventilator © Jones02461357 & Bartlett Learning, LLC 8 and work ©provided Jones by &the Bartlett respiratory Learning, muscles, this LLC NOT FOR SALE OR DISTRIBUTION becomes:NOT FOR SALE OR DISTRIBUTION ATC Pvent + Pmusc = elastance × volume 10 + resistance × flow From the equation, as volume and flow pressure © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC O) 5

2 assist from the ventilator approaches the elastic NOT FOR SALE OR DISTRIBUTION NOT FORand resistive SALE forces OR DISTRIBUTIONof the lung−thorax system, the pressure that must be generated by the respiratory 0 muscles (interpreted as work) will be diminished.

essure (cm H essure Pcirc Put another way, the equation describes the elastic Pr Ptrach –5 © Jones & Bartlett Learning, LLCand resistive loads contributing© Jones to the WOB.& Bartlett The Learning, LLC NOT FOR SALE ORPEEP DISTRIBUTIONventilator can perform someNOT or all FOR this work SALE thus, OR DISTRIBUTION “unloading” the ventilatory muscles. 024613578 Terms used are defined as follows: Time (seconds) Pvent (t): the inspiratory pressure generated by the ventilator as a function of time Fig©ure Jones 3-24 Automatic & Bartlett Tube Compensation Learning, (ATC) andLLC Pressure- © Jones & Bartlett Learning, LLC : the inspiratory pressure generated by SupportNOT Ventilation FOR (PSV) SALE Compared. OR DISTRIBUTION Pmusc (t)NOT FOR SALE OR DISTRIBUTION From Unoki T, Serita A, Grap, M. Automatic tube compensation during weaning from the ventilatory muscles as a function of time. mechanical ventilation: Evidence and clinical implications. Crit Care Nurse. 2008; 28(4):34−42. E: elastance of the respiratory system (lung and chest wall). Recall that elastance is the inverse of compliance. © Jones & ProportionalBartlett Learning, Assist Ventilation LLC © JonesV(t) & Bartlett: volume as Learning, a function of LLC time NOT FOR SALEProportional OR assistDISTRIBUTION ventilation (PAV) is an automated NOT FORR: respiratorySALE OR system DISTRIBUTION resistance form of ventilatory support that adjusts the level of V˙ (t): gas flow as a function of time support provided based on the patient’s measured E × V(t): the elastic load of the system. inspiratory flow, elastance, and resistance. The venti- R × V˙ (t): the resistive load of the system lator calculates the pressure© Jones required & Bartlett using an Learning,algo- LLC © Jones & Bartlett Learning, LLC rithm based on the equation of motion to achieve the clinician-set percentageNOT of supportFOR SALE (Box 3-9 OR). Pressure DISTRIBUTION NOT FOR SALE OR DISTRIBUTION varies depending on the amount of ventilatory flow and volume demanded by the patient and level of amplifica- of guided ventilatory support, while automatically tion selected by the clinician. The clinician may adjust adjusting to changing lung mechanics (compliance and the© percentage Jones & of Bartlettsupport from Learning, 5% to 95% LLCto achieve a resistance).© The Jones ventilator & Bartlett will deliver Learning, a pressure, flow,LLC WOBNOT in theFOR range SALE of about OR 0.3 DISTRIBUTION to 0.7 joules/L. Simply and volumeNOT based FOR on the SALE patient’s OR ventilatory DISTRIBUTION demand put, PAV employs a servo-targeting scheme in which the and lung mechanics without clinician-determined tidal support provided by the ventilator is proportional to the volumes or inspiratory pressures. This assumes intact patient’s inspiratory effort. patient neural control of respiration and a seal at the With PAV, the patient’s spontaneous inspiratory flow patient−ventilator interface (i.e., no leaks in the system). © Jones & functionsBartlett as Learning, an estimate ofLLC the neural output of the re- © JonesPAV is & available Bartlett on severalLearning, ventilators LLC (e.g., Covidien PB NOT FOR SALEspiratory OR centers. DISTRIBUTION PAV gained popularity as a mode us-NOT840, FOR PB SALE980). When OR using DISTRIBUTION PAV, a leak in the system can ing the patient’s inspiratory effort as the primary source be misinterpreted as increased patient effort and the

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inspiratory phase can continue into exhalation, like the PRVC allows for a patient trigger and the patient can © Jones & Bartlett Learning, LLC 29 © Jones & Bartlett Learning, LLC “runaway” phenomenon as described by Younes,. ThisNOT control FOR hisSALE or her OR respiratory DISTRIBUTION rate. Delivered pressure NOT FOR SALEcan be especially OR DISTRIBUTION problematic if using the ventilator to (and the associated volume) will change based on the deliver noninvasive ventilation (NIV) using a face mask, previous tidal breath. If the delivered tidal volume was which may develop leaks. less than the target, the pressure-control value will auto- PAV incorporates almost continuous input of the matically increase; if the tidal volume was greater than patient’s lung mechanics© Jones and effort. & Bartlett Modern Learning, venti- LLCthe target, the pressure-control© Jonesvalue will & automatically Bartlett Learning, LLC lators are capable ofNOT rapid FORelastance SALE and resistanceOR DISTRIBUTION decrease. Advantages of PRVCNOT include FOR maintaining SALE OR a DISTRIBUTION measures, allowing PAV to incorporate the equa- stable tidal volume delivery with pressure control in the tion of motion and function as a secondary source face of changing lung mechanics or changing patient of ventilatory work (in addition to the diaphragm). inspiratory effort. Potential problems include inappro- With PAV, ventilation is determined by the patient priate automatic pressure adjustments that may occur and© adequate Jones alarm& Bartlett settings Learning, must be maintained. LLC under certain© conditions.Jones & Bartlett Learning, LLC ProportionalNOT FOR assist SALE ventilation OR DISTRIBUTION is available on the Co- When usingNOT PRVC, FOR ventilators SALE ORsuch DISTRIBUTIONas the Servo- vidien PB 840 and PB 980, Phillips Respironics V60, i from Getinge will deliver a test tidal volume with a and Dräger Evita V500 (as “spontaneous proportional breath hold to measure the Pplateau. The plateauP is then pressure support.”) used to deliver the next breath and the exhaled VT is compared to the set VT. The tidal volume is delivered © Jones & DualBartlett Modes Learning, and Adaptive LLC Control © Jonesusing a& square Bartlett pressure Learning, waveform LLCand a decelerating flow waveform. The pressure is “regulated” to deliver NOT FOR SALEDual and OR adaptive DISTRIBUTION targeting modes of ventilation have NOT FOR SALE OR DISTRIBUTION the clinician set VT from breath to breath. If the volume been developed to combine the best characteristics of falls short or exceeds the set VT, the pressure can in- both pressure-and volume-control ventilation. When crease or decrease incrementally +/– 3 cm H2O for the using a single variable as the control, with pressure con- next breaths. trol, volume varied and with volume control, pressure The range of the auto-adjusting pressures are con- varied. With pressure-control© Jones ventilation, & Bartlett the risksLearning, of LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONfined to within 5 cm H2O of theNOT peak FOR pressure SALE alarm OR DISTRIBUTION under- or overventilation occur as patients’ lung me- setting and minimum set PEEP; an alarm will sound at chanics change. For example, as lung mechanics wors- both extremes. Animal studies on PRVC vs. VC ventila- ened with pressure-control ventilation, delivered tidal tion using a decelerating flow waveform have shown a volume may decline. With volume-control ventilation, significant reduction in the PIP using PRVC, although high airway pressures could occur with changes in lung gas exchange, lung mechanics, and the distribution of mechanics© Jones (e.g., & decreased Bartlett compliance Learning, or increasedLLC re- © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION ventilation didNOT not FOR appear SALE to be affected. OR DISTRIBUTION The reduced sistance). When using volume- or pressure-control ven- PIP associated with PRVC could lead to improved pa- tilation, ventilator alarms are set to monitor changes in tient outcomes, although the clinical evidence has not delivered volumes and pressures. Patient safety may be been definitive.30 PRVC is currently available on the compromised if alarms are silenced or ignored or set to Getinge Servo-i and Servo-u, CareFusion AVEA, Vyaire values that do not detect important changes. Dual tar- © Jones & Bartlett Learning, LLC © JonesVELA, & Covidien Bartlett PB Learning,840 and PB 980, LLC Hamilton G5, and geting allows the ventilator to switch between pressure Dräger Evita XL. NOT FOR SALEcontrol andOR volume DISTRIBUTION control during a single inspiration NOT FOR SALE OR DISTRIBUTION (i.e. within breath adjustment), while adaptive targeting allows the ventilator to automatically adjust pressure to Volume Support achieve the desired VT over several breaths (i.e. between Volume support (VS) can be used in spontaneously breath adjustment).14 © Jones & Bartlett Learning, LLCbreathing patients not requiring© Jones time-cycled, & Bartlett machine- Learning, LLC delivered breaths. Volume-support ventilation is like Pressure-Regulated Volume Control NOT FOR SALE OR DISTRIBUTIONpressure support, in that it is NOTpatient FOR triggered SALE and flowOR DISTRIBUTION Pressure-regulated volume control (PRVC) is designed cycled. However, with VS, the PSV level is automati- to deliver a volume-targeted, pressure-control breath. cally adjusted to achieve a volume target. Upon initia- An adaptive targeting scheme is employed in which tion, the ventilator sends a test pulse of 10 cm H2O the© ventilator Jones automatically& Bartlett adjustsLearning, pressure LLC between pressure above© Jones PEEP and & measuresBartlett lung Learning, compliance LLC breathsNOT to FOR reach SALEthe targeted OR volume DISTRIBUTION in response to and exhaledNOT tidal volume.FOR SALE VS uses OR that DISTRIBUTIONinformation to varying patient conditions. Delivered tidal volume is adjust pressure support to deliver the set tidal volume measured and compared to the set tidal volume. The on a breath-to-breath basis. In the absence of a patient pressure-control value is then gradually increased or de- trigger, VS does not have the option to set an adjustable creased until the target tidal volume is reached. Simply time-triggered backup rate. Volume support is available © Jones & put,Bartlett PRVC isLearning, a pressure-controlled LLC mode of ventilation© Joneson the & Getinge Bartlett Servo-i Learning, and Servo-u, LLC Covidien PB 840 NOT FOR SALEwith a backup OR DISTRIBUTION rate and set VT. NOTand FOR PB 980,SALE and ORNewport DISTRIBUTION e360.

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Automode © Jones & Bartlett Learning, LLC © Jonesaspects & of Bartlett pressure supportLearning, and pressure LLC control. With If a patient has a variable respiratory drive (fatigue, NOTASV, FOR the SALE ventilator OR adjusts DISTRIBUTION the mandatory respiratory NOT FOR SALE OR DISTRIBUTION rate and inspiratory pressure based on measurements irritability, pain, changing lung mechanics, and in- ˙ termittent apnea) a dual-control mode termed called of respiratory mechanics to deliver a target VE and pre- automode is available on some ventilators such as the scribed level of patient work (WOB); the ventilator will Getinge Servo-i and Servo-u. With automode, the ven- automatically adjust to changes in respiratory mechanics and patient inspiratory effort. tilator can automatically© Jones titrate the& Bartlettlevel of support Learning, pro- LLC © ˙Jones & Bartlett Learning, LLC vided between controlNOT and FORsupport SALE modes, OR dependent DISTRIBUTION With ASV, a set minimumNOT VE is FORmaintained SALE OR DISTRIBUTION on the patient’s level of spontaneous ventilation. Au- through self-adjusting pressure control and pressure- tomode can be set up to titrate the level of ventilation supported breaths; mandatory and spontaneous provided between the following modes: breaths are coordinated. Mandatory breaths are time triggered at a preset frequency and time cycled ■■ © VolumeJones control & Bartlett (VC)–volume Learning, support LLC (VS) (i.e., pressure© control).Jones &Mandatory Bartlett breath Learning, pressure LLC ■■ Pressure control (PC)–pressure support (PS) NOT FOR SALE OR DISTRIBUTION is set by theNOT ventilator. FOR Spontaneous SALE OR breaths DISTRIBUTION are ■■ PRVC–VS patient triggered and flow cycled (i.e., pressure support) and may occur between and during mandatory For example, automode can be set to alternate be- breaths. The clinician sets the inspiratory pressure tween PRVC and VS. In this mode, target minute venti- support level, rise time, and expiratory cycle sensitiv- lation (V˙ ) is based on the set tidal volume and set rate. E ity for spontaneous breaths. © Jones & PRVCBartlett mandatory Learning, breaths LLC and VS spontaneous breaths © Jones & Bartlett Learning, LLC Specifically, the Hamilton G5 ventilator uses an al- NOT FOR SALEare synchronized OR DISTRIBUTION using IMV. An adaptive pressure tar-NOT FOR SALE OR DISTRIBUTION gorithm to determine the optimal breathing frequency geting scheme is used in which V is measured and in- T and tidal volume. The ventilator uses the patient’s ideal spiratory pressure adjusted between breaths to achieve body weight (IBW) to determine a V˙ goal where the an average exhaled tidal volume equal to the set V tar- E T target V˙ is 100 mL/min/kg. This initial ˙ V setting can get. If the spontaneous respiratory rate does not achieve E E be altered by the clinician from 20% to 200% of the ma- the minimum minute© ventilation Jones & (based Bartlett on set Learning, tidal vol- LLC © Jones & Bartlett Learning, LLC chine–calculated V˙ . The V goal is calculated based ume and rate), mandatoryNOT breathsFOR SALEare time OR triggered. DISTRIBUTION A E T NOT FOR SALE OR DISTRIBUTION on the target minute volume (V˙ ) where V = V˙ /f. The spontaneously breathing patient would receive patient- E T E ventilator uses a test breath to determine compliance, triggered, pressure-support ventilation with a V target. T resistance, and autoPEEP. If the patient becomes apneic, automode increases the To setup ASV, the clinician enters the patient’s number of time-triggered, volume-targeted, pressure- weight and percent predicted minute ventilation to control© Jones breaths & needed Bartlett to achieve Learning, the set minimum LLC V˙ © Jones & Bartlett Learning, LLC E support (20% to 200%). The ventilator automatically (basedNOT on FOR set V SALEand f). OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION T sets minimum and maximum values for tidal volume, Automode can also be set up to use VC and VS or mandatory breath frequency, inspiratory pressure, and PC and PS to achieve the set minute ventilation. For inspiratory/expiratory time. example, a postoperative, apneic patient might be set Consistent with a lung protective strategy, tidal up to receive time-triggered VC ventilation using auto- volume is automatically decreased as compliance de- © Jones & mode.Bartlett If the Learning, patient begins LLC to breathe spontaneously, © Jones & Bartlett Learning, LLC creases. ASV can also automatically adjust rate and the ventilator will automatically switch to VS ventilation NOT FOR SALE OR DISTRIBUTION NOTI:E FOR ratio SALE to reduce OR the DISTRIBUTION risk of autoPEEP (i.e., autoPEEP and titrate the level of VC breaths using IMV to achieve limitation). Specifically, the ventilator automatically the minute volume goal (based on set V and f). Simply T adjusts mandatory breath frequency to keep the expira- put, automode is an interactive mode that switches be- tory time at least three time constants in length to mini- tween controlled and supported ventilation depending mize autoPEEP. on the patient’s effort.© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ASV will add or reduce the amount of support With automode, the clinician should be aware that NOT FOR SALE OR DISTRIBUTIONprovided to achieve the targetNOT V˙ . WhenFOR theSALE patient OR DISTRIBUTION inappropriate ventilator sensitivity settings resulting in E is breathing spontaneously, the mode shifts its focus accidental ventilator triggering (autotriggering) may be to pressure support while monitoring lung mechan- sensed as patient effort. The ventilator may then inap- ics and the target V˙ . With spontaneous breathing propriately reduce the frequency of machine-delivered, E at a sufficient minute ventilation, no mandatory time-triggered© Jones &breaths. Bartlett Appropriate Learning, alarm LLC settings, © Jones & Bartlett Learning, LLC breaths will be delivered. ASV also incorporates patientNOT monitoring, FOR SALE assessment, OR DISTRIBUTION and interprofessional NOT FOR SALE OR DISTRIBUTION unrestricted inspiratory flow. The ventilator auto- teamwork are at the heart of good patient care. matically reduces the level of support in response to increased patient effort, providing a form of automatic Adaptive Support Ventilation ventilator weaning. © Jones & AdaptiveBartlett support Learning, ventilation LLC (ASV) is another form © JonesASV & seems Bartlett well suitedLearning, to wean LLC patients from me- of closed-loop, automated ventilation that combines NOT FOR SALE OR DISTRIBUTION NOTchanical FOR SALE ventilation, OR but DISTRIBUTION unless properly monitored,

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© Jones &problems Bartlett a ssociatedLearning, with LLCventilatory muscle disuse © JonesHigh-Frequency & Bartlett Ventilation Learning, LLC atrophy from overly supported ventilation may result. NOT FOR SALE OR DISTRIBUTION NOTVarious FOR SALEforms of OR high-frequency DISTRIBUTION ventilation (HFV) ASV is available on the Hamilton G5, C3, C1, T1, and have been in use since the 1960s. High-frequency ven- MR 1. It should be noted that ASV operates differ- tilation employs very low tidal volumes, typically less ently from Adaptive Servo Ventilation (ResMed) or than physiologic dead space volume and very rapid Automatic Servo Ventilation (Respironics), two modes respiratory rates (> 60 to 3000 breaths/min). An ad- used in noninvasive treatment of complex or central 31 © Jones & Bartlett Learning, LLCvantage of HFV is the ability ©to Jonesventilate &patients Bartlett in Learning, LLC sleep apnea. NOT FOR SALE OR DISTRIBUTIONthe face of large air leaks andNOT indications FOR include SALE major OR DISTRIBUTION Pressure Augmentation and Volume-Assured airway disruption (e.g., tracheal esophageal fistula, bronchopleural fistula) that is unmanageable by con- Pressure Support ventional ventilation. HFV has also been advocated for Pressure augmentation, also known as known as use as a rescue technique in adult ARDS patients who volume-assured© Jones & pressure Bartlett support Learning, (VAPS), isLLC another are failing conventional© Jones & support Bartlett and inLearning, infants with LLC dual-controlNOT FOR mode SALE that monitors OR DISTRIBUTION gas flow and volume respiratory NOTfailure FORunresponsive SALE to OR conventional DISTRIBUTION me- during inspiration to ensure a preset VT is delivered. chanical ventilation. As originally introduced on the Bird 8400st (CareFu- HFV has been used extensively in neonates to sup- sion, Viasys Corporation, San Diego, California) the port patients with respiratory distress syndrome (RDS), mode delivered a patient-triggered, pressure-limited, and those with pulmonary air leaks and bronchopul- © Jones & flow-cycledBartlett Learning, breath (i.e., pressureLLC support). With VAPS,© Jonesmonary & dysplasiaBartlett to Learning, reduce mean LLCairway pressures. NOT FOR SALEinspiration OR begins DISTRIBUTION with a patient-triggered, pressure- NOTHigh-frequency FOR SALE ORventilation DISTRIBUTION reduces lung injury in support breath. As originally designed, the ventilator animal models and had promise in preventing broncho- then monitored inspiratory gas flow and volume during pulmonary dysplasia and volutrauma in very low-birth- the pressure-supported breaths. If the VT target volume weight infants with RDS. It is important to note that no was achieved before the inspiratory flow termination form of HFV has been shown to be consistently supe- criteria was reached,© the Jones ventilator & wouldBartlett cycle Learning, to ex- LLCrior to conventional ventilation© Jonesin reducing & mortalityBartlett Learning, LLC piration by volume. IfNOT the target FOR V TSALE was not OR achieved DISTRIBUTION and improving outcomes. NOT FOR SALE OR DISTRIBUTION before the inspiratory flow termination criteria was The U.S. Food and Drug Administration (FDA) de- reached, the ventilator maintained gas flow until the fines a high-frequency ventilator as a device that can volume was delivered. Thus, VAPS was similar to vol- deliver a respiratory rate >150 breaths/min. There are ume support (VS); however, tidal volume delivery was four major types of HFV that differ based on breath de- assured© Jones within &a breath, Bartlett while Learning, with VS, tidal LLC volume is livery design. © Jones & Bartlett Learning, LLC assuredNOT between FOR SALE breaths. OR DISTRIBUTION High-frequencyNOT FOR positive SALE pressure OR ventilation DISTRIBUTION (HFPPV) Earlier critical care ventilators that offered pressure generally uses tidal volumes in the range of 100 to 200 mL, augmentation or VAPS are no longer available (e.g., with respiratory rates of 60 to 120 breaths/min, which can Bear 1000, Bird 8400 ST,). Modes described as VAPS be accomplished using some conventional positive pres- are currently available with the Philips Respironics sure ventilators; HFPPV is rarely used today. © Jones & V6Bartlett and Respironics Learning, Trilogy LLC 202 (as average volume- © JonesHigh-frequency & Bartlett jet Learning, ventilation (HFJV)LLC was developed NOT FOR SALEassured ORpressure DISTRIBUTION support [AVAPS]) and the ResMed NOTin FOR 1956, SALE but only OR became DISTRIBUTION popular in the 1980s. HFJV Lumis Tx and ResMed Astral 100/150 (as intelligent tidal volumes can range from 3.5 to 4.5 mL/kg IBW volume-assured pressure support [iVAPS]). With with rates in the range of 100 to 200 breaths/min, al- AVAPS, time- or patient-triggered mandatory pressure though the Bunnell Life Pulse jet ventilator (Bunnell, control breaths and pressure-supported spontaneous Salt Lake City, Utah) can deliver frequencies in the breaths are provided.©17 IfJones the patient & Bartlett does not triggerLearning, a LLCrange of 240 to 660 cycles per© minute. Jones HFJV & Bartlett employs Learning, LLC breath within the intervalNOT determined FOR SALE by the OR rate DISTRIBUTION con- a jet delivered through a specialNOT endotracheal FOR SALE tube OR DISTRIBUTION trol, the ventilator delivers a pressure-control breath adapter; tidal volume is dependent on the amplitude, with the set I-time. If the patient triggers a breath jet driving pressure, size of the jet orifice, length of within the interval, the ventilator delivers a PSV breath. the pulsation, and the patient’s respiratory mechan- The pressure-control and pressure-support inspiratory ics. HFJV is commonly used in infants with typical pressure© Jones levels &are Bartlett continually Learning, adjusted over LLC time to delivered tidal© Jones volumes & in Bartlettthe range ofLearning, 1 to 3 mL at LLC achieveNOT the FOR volume SALE target. OR With DISTRIBUTION iVAPS, the ventilator a frequencyNOT of 420 FOR cycles SALE per minute. OR HFJVDISTRIBUTION is usu- delivers a variable (from breath to breath) PSV level to ally operated in combination with conventional CMV reach a clinician-set target alveolar ventilation. Thus, with PEEP. the ventilator drops the level of support as patient High-frequency percussive ventilation (HFPV) activity increases and conversely increases the PSV was developed by Forrest Bird in the mid-1980s © Jones & levelBartlett when patientLearning, activity LLC is too low. iVAPS also has a © Jonesand incorporates & Bartlett a slidingLearning, Venturi LLC he called a Pha- NOT FOR SALEbackup rate,OR ifDISTRIBUTION needed. NOTsitron. FOR HFPV SALE combines OR DISTRIBUTION high-frequency oscillatory

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© Jones &pulses (200 Bartlett Learning,to 900 bpm) and LLC small tidal volumes with © Jonesusing a& lung Bartlett protective Learning, strategy. HFOV LLC is not indicated pressure-control ventilation. HFPV may improve oxy- NOTfor FOR patients SALE with OR less severeDISTRIBUTION ARDS and is not recom- NOT FOR SALEgenation OR and DISTRIBUTIONventilation with reduced risk of baro- mended for routine use. When observing potential trauma and hemodynamic compromise; HFPV can regions of the pressure–volume curve (Figure 3-25) also be useful in promoting secretion clearance. HFPV, that increase the risk of lung injury, one can see the using the volumetric diffusive respirator (VDR), has value of ventilation within the two extremes of reduced been advocated for ventilation© Jones of & burn Bartlett patients Learning, with LLCcompliance. HFOV allows for© effective Jones ventilation& Bartlett while Learning, LLC inhalational injury toNOT maintain FOR low SALE peak airway OR DISTRIBUTIONpres- maintaining lung inflation betweenNOT FOR the extremes SALE ofOR atel- DISTRIBUTION sures; facilitate clearance of soot, sloughed mucosa, ectasis and over distention. and secretions; and to facilitate reinflation of collapsed HFOV uses a combination of mean airway pres- alveoli. HFPV may also decrease ICP in patients with sure, frequency, and amplitude to inflate the lungs and head injuries and reduce the incidence of pneumonia in promote O2 and CO2 exchange. Proximal airways and patients© Jones with smoke inhalation. & Bartlett Learning, LLC alveoli are ventilated© Jones by &bulk Bartlett gas flow, Learning, but as the lung LLC High-frequency oscillatory ventilation (HFOV) NOT FOR SALE OR DISTRIBUTION uses transitions toNOT the moreFOR distal SALE units, OR gas DISTRIBUTIONmoves by diffu- very small tidal volumes (50 to 250 mL) and very high sion. Possible mechanisms by which HFOV is thought frequencies in the range of 180 to 900 breaths/min to improve gas exchange include pendelluft, gas stream- (i.e., 3 to 15 Hz; 1 Hz = 60 breaths/min). HFOV is an ing, and Taylor-type dispersion. active form of high-frequency ventilation as a vibrat- Pendelluft is the gas exchange between lung units © Jones & ingBartlett diaphragm Learning, will create LLC both a positive (inspiration) © Joneswith different & Bartlett time Learning,constants. Recall LLC that time constants NOT FOR SALEand negative OR DISTRIBUTION(exhalation) wave. This wave is sent downNOT describe FOR SALE filling timeOR andDISTRIBUTION emptying time of lung units the respiratory tract as the pulse is sent “through” a and are affected by compliance and resistance. Differ- bias flow moving within the circuit. In ventilators em- ences in compliance and resistance in different regions ploying a passive form of high-frequency delivery, the of the lung can affect oxygenation and ventilation dur- exhalation cycle is a return to atmospheric or set PEEP. ing conventional positive pressure ventilation. Pen- During high-frequency© Jones ventilation, & Bartlett the Fio2 and Learning, mean LLCdelluft may allow for collateral© ventilation Jones & to Bartlett enhance Learning, LLC airway pressure affectNOT changes FOR in SALEoxygenation, OR DISTRIBUTIONand gas delivery during HFOV. NOT FOR SALE OR DISTRIBUTION frequency, amplitude, and TI influence ventilation Gas streaming during normal bulk gas flow (pH and Paco2). causes gas in the center of the airway to move more Currently, HFOV is the most commonly used form rapidly than gas near the airway walls due to frictional of HFV in neonates and adults. HFOV is the only mode effects (i.e., gas molecule to gas molecule in the center of ventilation© Jones available & Bartlett with theLearning, Vyaire 3100A LLC (neonates, and gas molecule© Jones to airway & Bartlett wall in the Learning, outer part of LLC the infants,NOT and FOR small SALE children) OR and DISTRIBUTION 3100B (adults and chil- gas stream).NOT While FOR an oversimplification, SALE OR DISTRIBUTION pulsatile gas dren > 35 kg) high-frequency oscillatory ventilators. flow during HFOV may move through the center of the In adults, the 3100B is primarily used as a rescue mode airways towards the gas exchange units, while gas flow for ARDS patients with refractory hypoxemia that has near the walls of the airways may move away from the failed to respond to conventional mechanical ventilation gas exchange units. This could result in simultaneous © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Injury

HFOV © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

CMV

Figure 3-25 The Pressure–Volume Curve. Areas in green show the oscillatory breaths and the region occupied within a pressure–volume © Jones & curve.Bartlett Conventional Learning, breaths that LLC operate in cases of pathology at the© extremes Jones of the& pressure–volumeBartlett Learning, curve may result LLC in atelectotrauma (low NOT FOR SALECL, bottom OR left regionDISTRIBUTION of the pressure–volume curve) or volutrauma (lowNOT CL, topFOR right SALEregion of theOR PV curve).DISTRIBUTION

9781284139860_CH03_095_154.indd 133 21/02/19 5:37 PM 134 CHAPTER 3 Principles of Mechanical Ventilation

© Jones &movement Bartlett ofLearning, “inspired” and LLC “expired” gases during © Jonespatients & withBartlett severe Learning,ARDS. There LLC are no universally HFOV. NOTagreed-upon FOR SALE indications OR DISTRIBUTION for HFV, although it has been NOT FOR SALETaylor-type OR DISTRIBUTION dispersion is simply enhanced diffu- suggested for several disease states and conditions sion of gas caused by the rapidly oscillating gas stream (e.g., bronchopleural fistula, severe ARDS, neonatal reaching the small airways. Enhanced diffusion is RDS, burns with inhalational injury, and head trauma thought to be the primary mechanism by which HFOV with increased ICP). HFV may cause autoPEEP due is effective in achieving© Jones gas exchange. & Bartlett Learning, LLCto reduced expiratory times and© Jones probably & should Bartlett be Learning, LLC In theory, HFOV NOTmay reduce FOR the SALE likelihood OR ofDISTRIBUTION avoided in patients with obstructiveNOT FOR lung disease, SALE as OR dy- DISTRIBUTION ventilator-associated lung injury (VALI) by achieving namic hyperinflation may occur. ventilation within an optimal lung compliance curve, avoiding pulmonary overdistention and repetitive Neurally Adjusted Ventilatory Assist alveolar collapse and re-expansion due to decreased resting© Jones lung volumes & Bartlett (i.e., decreased Learning, FRC due LLC to acute Neurally adjusted© Jones ventilatory & Bartlett assist (NAVA) Learning, uses the LLC Figure 3-26 restrictiveNOT FOR lung disease); SALE seeOR DISTRIBUTION. The HFOV natural electricalNOT discharge FOR SALE from the OR diaphragm DISTRIBUTION (i.e., volumes are usually close to the dead space volume and electrical activity of the diaphragm or EAdia) dur- controlled by the amplitude of the pressure pulse.32 ing inspiration to trigger a breath from the ventilator. Figure 3-26 illustrates possible mechanisms for gas dis- The inspiratory signal trigger is the primary differ- tribution during HFOV. ence between NAVA and other modes of mechanical 33 © Jones & BartlettIn summary, Learning, high-frequency LLC ventilation combines © Jonesventilation. & Bartlett The inspiratory Learning, signal LLC is detected using NOT FOR SALEvery rapid OR respiratory DISTRIBUTION rates with very small tidal vol- NOTdiaphragmatic FOR SALE electromyography OR DISTRIBUTION (EMGdia). While it is umes, at or below that of the physiologic dead space. possible to pick up EAdia using EMG from regions of the HFV has been used in neonates, pediatric patients, and chest wall, the best signals come from specifically de- adults. Its primary use in adults is as a rescue mode for signed esophageal catheters.

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Convection Direct ventilation of close alveoli NOT FOR SALE OR DISTRIBUTION Oscillatory pressure appliedNOT at FOR SALE OR DISTRIBUTION Proximal alveolar airway opening is damped by units are exposed to Turbulence flow-dependent resistance and central airway inertance of tracheal tube oscillatory pressures. and central airways. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION TurbulentNOT FOR flow SALE OR DISTRIBUTION and radial mixing

Asymmetric velocity profiles High peripheral resistance Convection increases pressure transmission Inspiratory velocity profile and diffusion to more proximal airways and Expiratory velocity profile nearby alveoli. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Atelectatic NOT FOR SALE OR DISTRIBUTIONPendelluft NOT FOR SALE OR DISTRIBUTIONAlveoli distal to a zone of compartments increased peripheral exposed to resistance, see low pressures increased due to decreased flow. oscillatory pressures © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Diffusion NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Laminar flow and radial mixing Diffusion © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Collateral NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONCardiogenic Expanded and aerated ventilation mixing alveoli protected from high oscillatory pressures

Figure 3-26 HFOV and Processes of Gas Distribution. © Jones & DataBartlett from Slutsky AS,Learning, Drazen JM. Ventilation LLC with small tidal volumes. N Engl J Med. 2002;© 347:631. Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

9781284139860_CH03_095_154.indd 134 21/02/19 5:37 PM Ventilator Modes 135

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC CLINICAL FOCUS 3-5 High-Frequency Ventilation in a Burn Patient NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Ms. Jones is a 27-year-old woman with second- and After 3 weeks of mechanical ventilation, third-degree burns covering her face, chest, abdo- operating room (OR) visits for debridement, multiple men, upper back, and right arm. Using the rule of bronchoscopies, and trips to the shower, the VDR set- nines (11 sections of the body, each equaling 9% of tings were weaned to oscillatory CPAP with a pulse the total body surface© Jones area + genitals& Bartlett 1%), it Learning, was frequencyLLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION estimated that 40.5% of her body was covered by of 500 Hz/5 cm H2O and a Fio2 of 40%. The patient burns that occurred due to an illicit drug operation was disconnected from the VDR to obtain extubation

explosion. Ms. Jones was a direct admit to the burn criteria and the MIP/NIF was –44 cm H2O, VT 400 mL, unit and was already intubated. She was taken to the RR 22, and rapid shallow breathing index (RSBI) shower© Jones for debridement, & Bartlett underwent Learning, bronchoscopy, LLC of 55. © Jones & Bartlett Learning, LLC andNOT had FOR vascular SALE access OR lines DISTRIBUTION placed. In the unit, she NOT FOR SALE OR DISTRIBUTION was placed on a volumetric diffusive respirator (VDR) Questions: for high-frequency percussive ventilation (HFPV) 1. Classify the initial two ABGs. secondary to signs and symptoms of inhalation lung 2. What happened while ventilating the patient in the injury, including particulate matter, erythema, exu- OR 5 days after admission? © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC date, and swelling in the airways. After ensuring a a. Classify the ABGs associated with the return NOT FOR SALEminimal OR cuff DISTRIBUTION leak of 10%, her initial VDR settings were:NOT FORfrom SALE the OR. OR DISTRIBUTION pulse frequency of 550 Hz, sinusoidal rate of 16, I:E b. What do you think the strategy was when con- ratio of 2:1 (TE = 2 sec), Fio2 100%, and PIP of 26 cm vective pressure was added? H O. Sedation by protocol was maintained with com- 2 3. Three weeks after admission, do you believe the pa- bination drug therapy including propofol, ketamine, © Jones & Bartlett Learning, LLCtient is ready for extubation?© Jones & Bartlett Learning, LLC and dilaudid. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Her initial ABG was: pH 7.27, Paco 60 mmHg, Pao – 2 2 Answers (pH/Paco2/Pao2/HCO3 ): 65 mmHg, and HCO – 27 mEq/L. The pulse frequency 3 1. 7.27 / 60 / 65 / 27. Partially compensated respira- was decreased to 500 Hz and the PIP was increased tory acidosis with mild hypoxemia. to 28 cm H2O. A follow-up ABG was pH 7.33, Paco2 7.33/ 54 / 70 / 28. Partially compensated respiratory © Jones & Bartlett Learning,– LLC © Jones & Bartlett Learning, LLC 54 mmHg, Pao2 70 mmHg, and HCO3 of 28 mEq/L. NOT FOR SALE OR DISTRIBUTION acidosis withNOT mild FOR hypoxemia. SALE Somewhat OR DISTRIBUTION better Five days after admission, the patient was taken to than the initial ABG. the operating room for debridement. She was taken Switching the patient from HFPV to PC-AC ap- off the VDR and placed on PC-AC ventilation at a PIP 2. peared to have resulted in derecruitment of lung of 22 cm H O, Fio 100%, RR 16, and PEEP +5. After 2 2 alveolar units and an increase in atelectasis. returning to the burn unit, an ABG was drawn: pH © Jones & Bartlett Learning, LLC – © Jonesa. 7.1 &7 /Bartlett 87 / 40 / 31.Learning, Partially compensated LLC respira- 7.17, Paco2 87 mmHg, Pao2 40 mmHg, and HCO3 of NOT FOR SALE OR DISTRIBUTION NOT FORtory SALE acidosis OR with DISTRIBUTION severe hypoxemia. 31 mEq/L. Her spontaneous RR and VT were 35 and 200 mL, respectively. Auscultatory findings were bilat- 7.36 / 58 / 148 / 32. Compensated respiratory aci- eral inspiratory crackles. She was placed back on the dosis with hyperoxemia.

VDR at an Fio2 of 100%, pulse frequency 500 Hz, si- b. The apparent strategy was to recruit the pre- nusoidal rate of 16,© and Jones I:E ratio & of Bartlett 2:1 (TE = 2Learning, sec). The LLCviously closed lung units© and Jones improve & the Bartlett Learning, LLC ˙ ˙ PIP was reduced toNOT 25 cm FORH2O and SALE a convective OR DISTRIBUTION pres- ventilation/perfusion (VNOT/Q) ratio. FOR SALE OR DISTRIBUTION sure of 10 cm H2O was added to improve ventilation 3. Yes. The RSBI is < 105 and the MIP/NIF is less than while maintaining a Paw < 35 cm H2O. A follow-up (more negative) –20 cm H2O. It appears that the ABG was pH 7.36, Paco2 58 mmHg, Pao2 148 mmHg, patient’s ventilatory failure has resolved. – and© Jones HCO3 of & 32 Bartlett mEq/L. Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

For normal inspiration to occur, a combination of duration of inspiratory contraction are related to lung cortical and medullary center outflow to the phrenic mechanics and respiratory drive. The ability of the dia- motoneurons is sent as a series of action potentials. The phragm to respond is dependent on the muscle’s inher- © Jones & activatedBartlett diaphragm Learning, contracts LLC and the intensity and © Jonesent contractile & Bartlett properties Learning, from breath LLC to breath. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

9781284139860_CH03_095_154.indd 135 21/02/19 5:37 PM 136 CHAPTER 3 Principles of Mechanical Ventilation

150 L/min RR b/min Flow 24 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC –150 NOT FOR500 ml SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Volume 358 VTe (ml) 60 µv © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Edi 43 NOT FOR SALE OR DISTRIBUTION NOT FOR SALEEdi peak OR (µV) DISTRIBUTION

O2 conc. PEEP NAVA level 30% 5 0, 4 cm H2O cm H2O/µV © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALEFigure 3-27OR TheDISTRIBUTION NAVA Screen on the Getinge Servo-u. The yellowNOT trace is FORactual pressure SALE delivery OR andDISTRIBUTION the gray trace is the estimated pressure delivery based on the diaphragm EMG signal and set NAVA level. From Getinge. The Basic Concept of NAVA and Edi NAVA modules 1 and 2. p. 17 (PPT slides: Training set from Servo-u sales rep).

NAVA provides coordination© Jones &of Bartlettthe patient’s Learning, cen- LLC ECG© Jones & Bartlett Learning, LLC tral respiratory driveNOT and the FOR ventilator’s SALE inspiratory OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION trigger. The ventilator can be set to cycle to expiration when the diaphragmatic signal reaches 40% to 70% of its maximum signal strength. The idea is to cycle to expiration based on a diminished inspiratory EAdia. This© isJones done to & prevent Bartlett continued Learning, inflation LLC by the ven- © Jones & Bartlett Learning, LLC tilator when the patient’s central respiratory control 40 NOT FOR SALE OR DISTRIBUTION 0 NOT FOR SALE OR DISTRIBUTION centers have switched to the expiratory phase. NAVA –40 is intended to improve patient–ventilator synchrony. Disadvantages include esophageal catheter cost, cath- Edi eter discomfort, catheter displacement, and apnea. In 20 10 © Jones & theBartlett case of apneaLearning, (or absence LLC of an EMGdia signal), the © Jones & Bartlett Learning, LLC ventilator will return to a pressure-controlled mode as 0 NOT FOR SALEa safety ORfeature. DISTRIBUTION NOT FOR SALE OR DISTRIBUTION The degree of NAVA support provided varies with the Figure 3-28 Placement of the NAVA Edi (Diaphragm EMG) amplitude of the diaphragmatic signal and the assist level Catheter. Correct placement is achieved when the second and third leads are highlighted in pink and the Edi signal is present. set by the clinician. The initial NAVA level applied should From Getinge. The Basic Concept of NAVA and Edi NAVA module 1 and 2, p. 38. PPT slides: produce the same inspiratory© Jones pressure & Bartlett (or slightly Learning, lower) LLCTraining set from Servo-u sales rep). © Jones & Bartlett Learning, LLC than the patient was receiving with conventional ventilation and then adjusted.NOT As NAVA FOR levels SALE are ORincreased, DISTRIBUTION NOT FOR SALE OR DISTRIBUTION peak pressure and tidal volume will increase. If the sup- the position of the EMG catheter for optimal sensing of port chosen is too low, the patient may exhibit signs of diaphragmatic activation/deactivation (Figure 3-28). distress with increased respiratory rate and a fatiguing NAVA has been used in adults, children, and neo- respiratory© Jones pattern. & Bartlett When the Learning, support is greater LLC than nates. In one© studyJones of 160 & randomlyBartlett assignedLearning, (con- LLC necessary,NOT FOR large tidalSALE breaths OR may DISTRIBUTION occur with suppression ventional mechanicalNOT FOR ventilation SALE vs.OR NAVA) DISTRIBUTION pediatric of the EMGdia signal. Optimal NAVA support allows the patients, there was a significant difference in sedation patient to choose a respiratory rate and VT to maintain (excluding opiates and postop patients) and length an appropriate Paco2 while sufficiently unloading the of pediatric ICU (PICU) stay indicating NAVA is a respiratory muscles. As with any mode of mechani- safe, effective form of ventilation that may improve 34 © Jones & calBartlett ventilation, Learning, proper alarm LLC settings are an important © Jonespatient–ventilator & Bartlett synchrony. Learning, NAVA LLC is available on Figure 3-27 NOT FOR SALEconsideration OR DISTRIBUTION when using NAVA. shows NOTthe FOR Getinge SALE Servo-i OR and DISTRIBUTION Servo-u ventilators. Currently, the Servo-u with NAVA capabilities. A graphic tracing there is no convincing evidence that NAVA improves display is used by the respiratory care clinician to adjust clinically important patient outcomes.

9781284139860_CH03_095_154.indd 136 21/02/19 5:37 PM Ventilator Parameters 137

© Jones &Ventilator Bartlett Learning, Parameters LLC © Jonesoperator & Bartlettselectable inspiratoryLearning, flow LLC waveforms for mandatory breaths. Older ventilators (e.g., Hamilton Ventilator parameters include pressures, flows, and NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Veolar) offered a choice of up to seven different inspi- volumes, as well as alarms and monitoring systems, as ratory waveforms (e.g., square wave, full down-ramp, described below. partial down-ramp, full up-ramp, partial up-ramp, sine Flow Waveforms wave, and accelerating flow). Most newer critical care © Jones & Bartlett Learning, LLCventilators offer a preset inspiratory© Jones flow & Bartlettwaveform orLearning, LLC Modern critical careNOT ventilators FOR provide SALE graphics OR DISTRIBUTION only a few options: square orNOT descending FOR ramp SALE (e.g., OR DISTRIBUTION packages that allow for observation and monitor- Covidien PB 840 and PB 960) or sine, square, and de- ing of pressures, flows, and volumes. Examination of celerating (e.g., Hamilton G5 and C3). Examples of pressure–time curves and flow–time curves can be flow, volume, and pressure waveforms are shown in very useful to identify the inspiratory trigger (e.g., Figure 3-29. Assuming a constant inspiratory time and patient-triggered© Jones & orBartlett time-triggered Learning, breaths), LLC the type of tidal volume© (VC Jones mode), & mean Bartlett and peak Learning, airway pres LLC- breathNOT (e.g., FOR mandatory SALE or OR spontaneous), DISTRIBUTION inspiratory gas sure will varyNOT in a predictableFOR SALE fashion OR withDISTRIBUTION changes flows and pressures, the cycle variable, and pressures in the inspiratory flow waveform. Generally, a down- and flows during expiration. The pressure–time wave- ramp will result in the lowest PIP but highest mean form display, also known as the pressure–time scalar, airway pressure, while an up-ramp will tend to result can be very useful in identifying the mode of ventilation in the highest PIP but lowest mean airway pressure. © Jones & asBartlett well as PIP, Learning, Pplateau, and LLCbaseline pressure (e.g., PEEP © JonesPut another & Bartlett way, flow Learning, waveforms LLC that tend to increase NOT FOR SALEor CPAP). OR Observation DISTRIBUTION of the pressure–time scalar NOTmean FOR airway SALE pressure OR DISTRIBUTION also decrease PIP and vice versa. can also provide a visual representation of the inspira- Increasing mean airway pressure may be helpful to tory time, expiratory time, and I:E ratio. Volume–time improve oxygenation and gas transfer, while reducing curves provide visual confirmation of the patient’s ac- mean airway pressure may improve venous return and tual inspired and expired tidal volumes. reduce the likelihood of cardiovascular compromise. The flow–time ©curve Jones orflow–time & Bartlett scalar provides Learning, LLCThe square waveform is a ©common Jones flow & Bartlett pattern Learning, LLC a graphic display of theNOT inspiratory FOR SALE and expiratory OR DISTRIBUTION gas offered on most mechanical NOTventilators FOR during SALE VC OR DISTRIBUTION flow versus time. For mandatory breaths, the most ventilation. With the square wave, volume and pres- common flow waveforms are the constant flow wave- sure increase in a linear fashion (Figure 3-29B). With a form (also known as the square wave, rectangular wave, down-ramp type flow waveform, pressure and volume or constant flow generator) and the decreasing flow tend to increase in a curvilinear fashion (Figure 3-29D). waveform© Jones (also & known Bartlett as the Learning, down-ramp, LLCdecelerat- A sine wave© flow Jones waveform & Bartlett results in Learning, a sinusoidal LLC ingNOT flow, FORor descending SALE ramp).OR DISTRIBUTION During VC ventilation increase in NOTvolume FOR and then SALE an increase OR DISTRIBUTION in pressure (VC-CMV and VC-IMV), several ventilators offer followed by a decrease in pressure at end-inspiration

NOT FOR SALE OR0 DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Flow (L/min)

–100

2 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION essure Pr (cm H 0

1. 0 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC lume NOT(L) FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Vo 0 (A) 1234(B) 1 234(C) 1234(D) 1234(E) 1234

© Jones & FBartlettigure 3-29 Learning, Pressure, Volume, LLC and Flow Waveforms.35 (A) Descending© (decelerating)Jones & flow Bartlett waveform and Learning, square wave pressure LLC waveform. (B) Square wave flow waveform with linearly increasing pressure waveform. (C) Up-ramp flow waveform with increasing pressure waveform. (D) Down-ramp flow NOT FOR SALEwaveform ORwith curvilinear DISTRIBUTION increasing pressure waveform. (E) Sine or sinusoidalNOT flow FOR waveform SALE with increasing OR DISTRIBUTION and then decreasing pressure waveform. Tobin MJ. Principles and Practice of Mechanical Ventilation. 2nd ed. New York, NY: McGraw-Hill; 2006: 41.

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© Jones &(Figur Bartlette 3-29E). Learning, The sine LLCflow waveform is thought to © JonesRC &Insight Bartlett Learning, LLC more closely resemble gas flow during normal, spon- NOT FOR SALE OR DISTRIBUTION NOT FOR SALEtaneous ORbreathing. DISTRIBUTION The ascending, accelerating, or In the volume-control mode, decreases in com- up-ramp flow waveforms generally are not available on the current generation of critical care ventilators pliance will increase the PIP and Pplateau. In the (Figure 3-29C). pressure-control mode, decreases in compliance Flow waveforms during© Jones pressure-control & Bartlett ventila Learning,- LLCwill decrease delivered VT; ©peak Jones inspiratory & Bartlett pres- Learning, LLC sure will remain the same. tion (PCV) and pressure-supportNOT FOR SALEventilation OR (PSV) DISTRIBUTION NOT FOR SALE OR DISTRIBUTION generally are descending or decelerating, resulting in a square-wave–like pressure waveform (Figure 3- 29A). With PCV and PSV, initial peak flow is rapidly The difference between PIP and Pplateau is due to air- achieved during the beginning of inspiration and then way resistance (Raw), which can also be easily calcu- = flow© Jonesdecreases & until Bartlett the breath Learning, terminates LLC (Figure 3- lated during© VC Jones ventilation & Bartlett where: Raw Learning, (PIP – P plateauLLC) ÷ inspiratory flow rate. Normal CST is 60 to 100 mL/cm 29ANOT). With FOR PCV, SALE inspiration OR cycles DISTRIBUTION to expiration by NOT FOR SALE OR DISTRIBUTION time, with flow continuing to decrease until the set H2O while normal Raw in intubated patients is about inspiratory time is reached. During PCV, if adequate 5 to 10 cm H2O/L/sec, depending on the diameter of the inspiratory time is allowed, flow will reach zero at end endotracheal tube and inspiratory gas flow rate. Bron- inspiration followed by an inspiratory pause or hold chospasm, increased secretions, mucosal edema, mucus © Jones & (i.e.,Bartlett no flow). Learning, With PSV, LLCinspiratory flow declines © Jonesplugging, & Bartlett or endotracheal Learning, tube occlusion LLC (secretions, kinking, or biting) may increase Raw. During volume NOT FOR SALEuntil the OR flow DISTRIBUTION termination criterion is met, generally NOT FOR SALE OR DISTRIBUTION 5% to 25% of the peak flow or 5 L/min. Most modern ventilation, PIP will increase with decreases in compli- ventilators allow for adjustment of inspiratory rise ance OR increases in resistance. With increased Raw, time and expiratory sensitivity during PSV and these the PIP – Pplateau difference will increase. With decreased Figure 3-30 adjustments will alter the inspiratory pressure and compliance, the Pplateau will increase ( ). flow waveforms. © Jones & Bartlett Learning, LLCInspiratory pause can also© be Jones applied to& improveBartlett the Learning, LLC distribution of inspired gases and may improve gas ex- NOT FOR SALE OR DISTRIBUTIONchange. Devaquet et al. showedNOT that FOR inspiratory SALE pause OR DISTRIBUTION Inspiratory Pause < 1 second over normal I times could increase CO2 Most modern mechanical ventilators allow the clini- removal by 6 mmHg in patients with ARDS ventilated cian to set an inspiratory pause or hold in the VC mode, with low lung volumes and keep measured autoPEEP < 36 which© Jones will result & inBartlett an inspiratory Learning, pressure LLC plateau 0.5 cm H©2O. Jones & Bartlett Learning, LLC (PplateauNOT). For FOR example, SALE with OR the DISTRIBUTION Hamilton G5, an inspi- NOT FOR SALE OR DISTRIBUTION ratory pause may be set by the operator between 0% RC Insight and 70% of cycle time, while the CareFusion AVEA and Covidien PB 840 allow the clinician to set an in- In the VC mode, increases in airway resistance spiratory hold from 0 to 3 seconds and 0 to 2 seconds, (Raw) will increase PIP and increase the respectively. The inspiratory pause is designed to hold © Jones & Bartlett Learning, LLC © JonesPIP –& P Bartlett difference. Learning, LLC the inspired breath momentarily prior to the exhalation plateau NOT FOR SALEphase. Clinicians OR DISTRIBUTION and automated monitoring systems NOT FOR SALE OR DISTRIBUTION incorporated within the ventilator routinely use this Fio2 feature to make determinations of lung mechanics, compliance, and resistance. When inspiratory pause is When initiating mechanical ventilation, the clinician must consider appropriate choice of fractional inspired activated, the airway© pressure Jones will & decrease Bartlett from Learning, PIP to LLC © Jones & Bartlett Learning, LLC a Pplateau, and the plateau will continue for the duration oxygen (Fio2) concentration, based on the patient’s of the inspiratory pause.NOT With FOR a sufficient SALE ORinspiratory DISTRIBUTION NOT FOR SALE OR DISTRIBUTION plateau (0.5 to 2 sec), there should be complete equili- Increased airway Decreased bration between Pplateau and alveolar pressure. Under resistance compliance these circumstances, plateau pressure represents the PIP PIP force© Jonesrequired &to distendBartlett the Learning, lung within the LLC thorax at © Jones & Bartlett Learning,Raw LLC a point of no gas flow. Total static compliance (CST) can Raw P NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONplat then be easily calculated where: CST = VT ÷ (Pplateau – Pplat PEEP). CST is determined by the patient’s lung compliance and thoracic or chest wall compliance. Atelectasis, pneumonia, pulmonary edema, ARDS, and pulmonary (A)(B) © Jones & fibrosisBartlett will Learning, all decrease lungLLC compliance. Thoracic cage© Jones & Bartlett Learning, LLC FIGURE 3-30 Evaluation of the Peak and Plateau Pressures Using a NOT FOR SALEdeformities, OR ascites,DISTRIBUTION obesity, and pregnancy will all de- NOT FOR SALE OR DISTRIBUTION crease thoracic compliance. Pressure–Time Curve.

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© Jones &clinical Bartlett condition Learning, and therapeutic LLC goals. Modern critical© Jonesgenerally & Bartlettrefers to positive Learning, end-expiratory LLC pressure ap- care ventilators allow from 21% to 100% oxygen to be plied following a time-triggered or patient-triggered NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION provided (Fio2 0.21 to 1.0). Fio2 and barometric pres- mandatory breath. CPAP generally refers to continu- sure (PB) determine the partial pressure of inspired oxy- ous positive airway pressure applied to spontaneously gen (PIO2) and PIO2 and alveolar ventilation determine breathing patients. With IMV, mandatory breaths are the alveolar oxygen tension (Pao2) where: interspersed with spontaneous breaths; some refer to this as PEEP/CPAP. PIO2 (mmHg)© Jones = Fio 2& (P BBartlett – PH2O) Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONPEEP and CPAP increase FRC,NOT improve FOR SALE and main- OR DISTRIBUTION and the alveolar air equation: tain lung volumes, and help open and stabilize alveoli in patients with acute restrictive disease. As noted, small 1 – Fio2 Pao2 = Pio2 – Paco2 Fio2 + amounts (3 to 5 cm H2O) of PEEP or CPAP generally ( R ) are used in most intubated patients receiving mechanical ventilatory support to avoid end-expiratory alveolar Paco© Jonesis the alveolar & Bartlett carbon dioxideLearning, tension LLC (which © Jones & Bartlett Learning, LLC 2 collapse, which may be caused by the loss of normal approximatelyNOT FOR equals SALE Paco OR2) and DISTRIBUTION R = the respiratory NOT FOR SALE OR DISTRIBUTION glottic function; this is sometimes referred to as physi- quotient (which is simply CO production divided by 2 ologic PEEP. Applied PEEP may also be helpful to offset oxygen consumption; R = V˙ CO /V˙ O ). Normal R is 2 2 the effects of autoPEEP and air trapping. Patients with about 0.80. obstructive lung disease often already have an elevated Clinically, alveolar oxygen tension (Pao ) can be ap- 2 FRC, and PEEP should be used cautiously in these pa- © Jones & proximatedBartlett Learning,by the simplified LLC alveolar air equation where:© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOTtients, FOR except SALE to offset autoPEEP.OR DISTRIBUTION Pao2 = PIO2 – Paco2/0.80 Higher PEEP levels are often used in patients with hypoxemic respiratory failure (e.g., ARDS, pneumonia, Thus, things that will increase Pao2 include increased and pulmonary edema) to improve oxygenation and Fio2, increased PB, and decreased Paco2. avoid VALI. PEEP or CPAP is indicated in patients with As Pao increases, so does arterial oxygen tension 2 © Jones & Bartlett Learning, LLCcollapsed and unstable lung units,© Jones and arterial & Bartlett oxy- Learning, LLC (Pao2); however, the relationship between Pao2 and NOT FOR SALE OR DISTRIBUTIONgenation is inadequate when NOTusing moderateFOR SALE to high OR DISTRIBUTION Pao2 is dependent on the matching of gas and blood in concentrations of oxygen. PEEP/CPAP should be con- the lung (V˙/Q˙ ) and gas diffusion across the alveolar cap- sidered when Pao2 < 60 mmHg and Fio2 > 0.40. illary membrane into the blood. PEEP and CPAP increase mean airway pressure, which Respiratory failure is a usual prelude to mechanical may impede venous return and compromise cardiac out- ventilation and as such, there are usually oxygenation © Jones & Bartlett Learning, LLC put in certain© patients.Jones Untreated & Bartlett tension Learning, pneumothorax LLC problems that will need attention. As noted, Fio2 is an NOT FOR SALE OR DISTRIBUTION is an absoluteNOT contraindication FOR SALE to theOR application DISTRIBUTION of PEEP important contributor to alveolar and arterial oxygen or CPAP. PEEP/CPAP should be used cautiously (if at all) partial pressures. Pao2, in turn is an important determi- in patients with hemodynamic instability, hypotension, nant of the oxygen saturation of the hemoglobin (Sao2) shock, already elevated FRC (e.g., COPD, acute asthma), and arterial oxygen content (Cao2). Oxygen delivery to and elevated ICP. It is also important to note that not ˙ the tissues (Do2) requires an adequate Cao2 and car- all ARDS patients respond to low-level PEEP and high © Jones & Bartlett Learning,˙ LLC˙ = × ˙ © Jones & Bartlett Learning, LLC diac output (QT); recall that Do2 Cao2 QT. When levels of PEEP may improve outcomes in severe ARDS. NOT FOR SALEoxygen demandOR DISTRIBUTION outstrips supply, the clinician will NOTThere FOR areSALE also pulmonary OR DISTRIBUTION and extrapulmonary causes of note an increasing lactate concentration as anaerobic ARDS. Pulmonary causes include infectious pneumonia metabolism replaces the Krebs cycle metabolism for while extrapulmonary causes include sepsis, hemorrhagic ATP generation. shock, peritonitis, and multiple trauma. Extrapulmonary O2 is well tolerated in the clinical setting, though causes of ARDS may respond better to low levels of PEEP © Jones> & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC excessive concentrations (Fio2 0.50 to 0.60) for pro- than pulmonary causes. longed periods may leadNOT to FORadverse SALE effects OR(e.g., DISTRIBUTION oxygen NOT FOR SALE OR DISTRIBUTION toxicity, absorption atelectasis). Adequate oxygenation must be maintained to prevent tissue hypoxia and lactic Alarms acidosis. However, the lowest possible combination of Industry has continually been making improvements Fio and PEEP should be used to keep the Pao between ©2 Jones & Bartlett Learning, LLC2 in ventilator© alarms. Jones Alarm & Bartlett sensitivity Learning, can be set by LLC 60 and 80 mmHg and Sao2 between 90% and 96% for NOT FOR SALE OR DISTRIBUTION the respiratoryNOT care FOR clinician SALE to provide OR DISTRIBUTION high and low most patients. alarms for specific parameters such as volume, pres- PEEP/CPAP sure, respiratory rate, minute ventilation, Fio2, and the development of apnea. Alarms systems often incorpo- Positive end-expiratory pressure (PEEP) and continuous rate algorithms to assign importance from high to low © Jones & positiveBartlett airway Learning, pressure (CPAP)LLC should be considered © Joneswith color & Bartlett and volume Learning, differentiation. LLC Ventilator alarms NOT FOR SALEalongside OR Fio DISTRIBUTION2 when addressing oxygenation issues NOTshould FOR beSALE adjusted OR to DISTRIBUTIONensure clinicians are alerted when in patients requiring mechanical ventilation. PEEP their attention is required, yet overly sensitive alarm

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settings should not result in frequent nuisance alarms, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC BOX 3-10 Alarm Levels of Priority which are then ignored. Put another way, the percentageNOT FOR SALE OR DISTRIBUTION NOT FOR SALEof true positive OR DISTRIBUTION alarms should be high, and the number Level 1 of false positive alarms should be low to ensure patient safety while minimizing unnecessary environmental 1. Power failure noise pollution in the ICU. To that end, The Joint Com- 2. Control circuit failure mission (which accredits© Jones health care& Bartlett organizations Learning, and LLC3. High or low primarily line© presJonessure & Bartlett Learning, LLC programs) has issued National Patient Safety Goals (ef- NOT FOR SALE OR DISTRIBUTION4. Exhalation valve failureNOT FOR SALE OR DISTRIBUTION fective 1/2017) addressing all medical devices equipped with alarms.37 Level 2 These goals reference a 2014 UCSF study that found 1. Humidification failure an average of 187 audible alarms/bed/day; 45% were for 2. High or low PEEP arrhythmias© Jones and & 88.8% Bartlett were falseLearning, alarms, resulting LLC in © Jones & Bartlett Learning, LLC 38 3. Fio2 blender control failure alarmNOT fatigue FOR and SALE desensitization. OR DISTRIBUTION A sentinel event is NOT FOR SALE OR DISTRIBUTION defined by The Joint Commission as any unanticipated 4. Circuit leak event in a healthcare setting resulting in death or seri- 5. Circuit occlusion ous physical or psychological injury (not related to the Level 3 natural course of the patient’s illness). Alarms are at © Jones & theBartlett heart of Learning, a Joint Commission LLC statement on sentinel © Jones1. AutoPEEP & Bartlett Learning, LLC ˙ NOT FOR SALEevent alerts, OR suggestingDISTRIBUTION a need for better alarm thresh-NOT FOR2. High SALE or low OR VE DISTRIBUTION olds and improved routing of alarms to the appropriate 3. High or low VT responder. High or low peak pressures During mechanical ventilation, there are factory-set, 4. priority alarms that signal power failure, high and low *It should be noted that Level 1 alarms are noncancelling and source machine pressures,© Jones and temperature. & Bartlett Clinician- Learning, LLCmust be corrected prior to reinitiation© Jones of mechanical & Bartlett ventilation. Learning, LLC set alarms are determined from patient to patient and Level 3 alarms may also trigger a Level 2 alarm. NOT FOR SALE OR DISTRIBUTION**All alarms must be attended toNOT in the interests FOR ofSALE patient OR DISTRIBUTION dependent on institutional protocols and clinician expe- safety. Appropriate settings, alarm limits, and patient thera- rience. Examples of common clinician settings include: ˙ pies (e.g., bronchodilators, suctioning, and sedation) must be low tidal volume set 100 mL below set VT, low VE set 2 considered. ˙ L/min below observed VE (total machine + spontaneous),© highJones respiratory & Bartlett rate set Learning, 10 bpm above LLC observed © Jones & Bartlett Learning, LLC + rateNOT (total FOR machine SALE spontaneous), OR DISTRIBUTION PEEP set 2 to 5 NOT FOR SALE OR DISTRIBUTION cm H2O below set PEEP, and a peak pressure alarm set patient ventilatory parameter fluctuations including 5 to 10 cm H2O above observed PIP. Importantly, the alarms should be set to notify the clinician of problems volume loss or lung mechanics alterations. In addition that could jeopardize patient safety or lead to such sen- to these alarms, the clinician should consider supple- tinel events as injury or death. For instance, appropriate mentary systems that are routinely used for ventilatory © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, monitors LLC and end-tidal CO alarms for minute ventilation could signal a loss of the monitoring such as Spo2 2 monitors (i.e., P CO ). Assessments of ventilation using NOT FOR SALEspontaneous OR DISTRIBUTIONcontribution of ventilation post-analgesic NOT FOR SALE ETOR 2DISTRIBUTION P CO can provide the clinician with real-time changes administration. Ventilator alarms should notify nursing, ET 2 in gas exchange status; however, clinicians must under- medical, and respiratory care personnel of deterioration stand the limitations of P CO for patient monitoring. in the patient’s ventilatory support status before this ET 2 Oximetry and end-tidal CO2 monitoring should have deterioration manifests as cardiac arrhythmias or O2 © Jones & Bartlett Learning, LLCappropriate alarm limits set and© Jonesbe managed & Bartlett by the re- Learning, LLC desaturation. 39 The priority of alarmsNOT for FOR mechanical SALE ventilation OR DISTRIBUTION sponsible clinicians. ChaptersNOT 8 and FOR 9 discuss SALE patient OR DISTRIBUTION have been assigned three levels of importance as de- assessment and monitoring in more detail. Box 3-10 scribed in . Level 1 alarms require immediate Humidification attention, cannot be silenced, and are life threatening. In ©the Jones event of &a ventilator Bartlett alarm Learning, signal, the LLC patient Primary functions© Jones of the & normal Bartlett upper Learning, airway are toLLC shouldNOT be FOR immediately SALE disconnected OR DISTRIBUTION from mechanical warm, filter,NOT and FORhumidify SALE inspired OR gases. DISTRIBUTION The isother- ventilation and ventilated manually (via resuscitation mic saturation boundary (ISB) is the point at which bag with 100% Fio2) until the problem can be identified inspired gases are 100% saturated at body tempera- and corrected. Replacing the ventilator with another ture, which occurs two to three subdivisions below the unit should be immediately considered if the problem trachea. By the time inspired gas reaches the ISB, the © Jones & cannotBartlett be readily Learning, identified. LLC Level 2 alarms may be life © Jonesinspired & airBartlett has been Learning, warned to 37ºC LLC and humidified NOT FOR SALEthreatening, OR ifDISTRIBUTION left unattended. These alarms may be NOTto FOR 44 mg SALE H2O/L ORwith DISTRIBUTIONa water vapor pressure (PH2O) of self-limiting with audible termination if normal function 47 mmHg. During invasive mechanical ventilation, the resumes. Level 3 alarms are generally associated with normal anatomy of the upper airway is bypassed, and

9781284139860_CH03_095_154.indd 140 26/02/19 12:36 PM Ventilator Parameters 141

© Jones &these Bartlett primary Learning, functions of LLC the upper airway are lost. © Jonescan increase & Bartlett secretion Learning, viscosity and LLC impair mucociliary Systems to provide humidification during mechanical NOTtransport. FOR SALE Proper OR management DISTRIBUTION of heated humification NOT FOR SALEventilation OR include DISTRIBUTION active humidification using a heated systems during mechanical ventilation should aim to humidifier and passive humidification using a heat and ensure adequate humidification while avoiding the po- moisture exchanger (HME). American Association for tential for thermal injury or hyperthermia due to exces- Respiratory Care Clinical Practice Guidelines for active sive temperatures. It is of interest to note that airway humidification during© invasiveJones &mechanical Bartlett ventilation Learning, LLCrewarming using a heated humidifier© Jones may & provideBartlett a Learning, LLC suggest humidificationNOT should FOR be SALEprovided OR to achieve DISTRIBUTION modest benefit for adult patientsNOT suffering FOR SALE from acci-OR DISTRIBUTION between 33 to 44 mg H2O/L at gas temperatures be- dental hypothermia; however, airway rewarming is not tween of 34º to 41ºC (100% relative humidity) at the a primary form of treatment in these patients. ventilator circuit connection to the artificial airway (i.e., Y-connector). This may be accomplished by several Sigh Breaths heated© Jones humidifiers & Bartlett designed Learning,to be used with LLC mechanical © Jones & Bartlett Learning, LLC Normal, spontaneously breathing individuals take an ventilatorsNOT FOR (e.g., FisherSALE Paykel OR orDISTRIBUTION Conchatherm heated NOT FOR SALE OR DISTRIBUTION humidifiers). When using a heat moisture exchanger intermittent deep breath or sigh every 6 to 10 minutes (HME) to achieve passive humidification during invasive to keep alveolar units inflated and prevent atelectasis. In mechanical ventilation, the device should deliver 30 mg the absence of PEEP, constant, shallow tidal breathing < H2O/L. Passive humidification is not recommended for ( 7 mL/kg) without a sigh may result in progressive © Jones & patientsBartlett receiving Learning, NIV or LLCfor patients being ventilated © Jonesatelectasis. & Bartlett Therefore, Learning, postoperative LLC abdominal or thoracic surgical patients are instructed to cough and deep NOT FOR SALEwith low OR tidal DISTRIBUTION volumes (e.g., lung-protective ventilation)NOT FOR SALE OR DISTRIBUTION because the HME will add to dead-space volume.40 breathe to prevent the development of postoperative The International Organization for Standardization atelectasis and respiratory failure. (ISO) suggests increased thermal injury risk at sustained Volume ventilation became common in the ICU in inspired gas temperatures > 41ºC and active humidi- the late 1960s and early 1970s when more sophisticated fiers and humidifier© alarm Jones limits & shouldBartlett be set Learning, accord- LLCmechanical ventilators were introduced.© Jones These& Bartlett ven- Learning, LLC ingly. The AARC ClinicalNOT PracticeFOR SALE Guideline OR for DISTRIBUTION active tilators often included a sigh NOTfunction. FOR Tidal SALE volumes OR DISTRIBUTION humidification recommends “high temperature be set were generally set in the normal range of 5 to 7 mL/ no higher than 41ºC (with a 43ºC over-temperature kg IBW and intermittent sigh breaths of 1.5 to 2 × VT alarm) and the low-temperature alarm should be set no were provided every 6 to 10 minutes. Multiple sighs in lower than 2ºC below the desired temperature at the a row could be set on some ventilators. Sigh breaths are 39 circuit© Jones Y-piece.” & HeatingBartlett and Learning, humidification LLC of the known to prevent© Jones alveolar & Bartlettderecruitment Learning, and associ- LLC airwaysNOT is FORan important SALE component OR DISTRIBUTION of body homeosta- ated airwayNOT problems FOR that SALE lead to ORventilation–perfusion DISTRIBUTION sis and bronchial hygiene. Inadequate humidification mismatch and intrapulmonary shunt (Figure 3-31).

0.8 SIGH

0.4 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR0 DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Flow (L/min) Flow –0.4

–0.8

0.6 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 0.4 VT,S NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION lume (L) 0.2 VT,PSV Vo 0

40 O) © Jones2 30 & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Plat NOT FOR20 SALE OR DISTRIBUTIONs NOT FOR SALE OR DISTRIBUTION w (cm H 10 Ti,s Pa 0 02461 3578 9110 11123151 14 1671 18 9 20 Time (seconds) © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALEFIGURE 3-31OR ADISTRIBUTION Machine-Delivered Sigh Breath.42 NOT FOR SALE OR DISTRIBUTION From Patroniti N, Foti G, Cortinovis D, et al. Sigh improves gas exchange and lung volume in patients with acute respiratory distress syndrome undergoing pressure support ventilation. Anesthes. 2002;96(4):788–794.

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© Jones & BartlettBeginning Learning, in the mid-1970s, LLC larger tidal volumes in © Jonesto choose & Bartlett an Fio2 ranging Learning, from 0.21 LLC to 1.0 and the ef- the range of 10 to 15 mL/kg were often applied using NOTfect FOR of Fio SALE2 on alveolar OR DISTRIBUTION oxygen tension (Pao2) is highly NOT FOR SALEintermittent OR mandatoryDISTRIBUTION ventilation (IMV). The use of predictable (see the earlier discussion on the alveolar larger tidal volumes made the use of sigh breaths un- air equation). Gas transfer across the alveolar capillary necessary. However, it became apparent following the membrane, however, is dependent on many factors. initiation of the ARDSNet, launched in 1994, that large There are four general mechanisms that may cause tidal volumes of 12 mL/kg© Jones (predicted & Bartlett body weight) Learning, re- LLChypoxemia: hypoventilation, ©ventilation Jones perfusion& Bartlett mis- Learning, LLC ˙ ˙ < > ˙ ˙ = sulted in increased mortalityNOT FOR as compared SALE toOR small DISTRIBUTION tidal match (i.e., V/Q 1 but 0),NOT shunt FOR(V/Q SALE 0), and OR dif- DISTRIBUTION volumes (6 mL/kg) with Pplateau ≤ 30 cm H2O. fusion impairment. Today, it is recommended that most patients, includ- Hypoxemia due to hypoventilation can sometimes be ing those with normal lungs, receive at least 5 cm H2O partially or fully reversed with the restoration of normal of PEEP to prevent atelectasis and that tidal volumes ventilation and Paco2. Such patients may have other- and© pressures Jones be & limited Bartlett (e.g., Learning, VT of 4 to 8 mL/kg; LLC Pplateau wise normal© lung Jones function & Bartlett(e.g., neuromuscular Learning, disease, LLC < 28NOT to 30 FOR cm H 2SALEO); sigh ORbreaths DISTRIBUTION are unnecessary. That postoperativeNOT patients FOR who SALE have been OR heavilyDISTRIBUTION sedated, said, it could be stated that recruitment maneuvers used and drug overdose without aspiration), and initiation of in patients with ARDS represent a form of intermittent mechanical ventilatory support may correct their hy- hyperinflation of the lung (i.e., a sigh). Sigh breaths may poxemia. Hypoxemia due to low V˙/Q˙ (e.g., V˙/Q˙ < 1 but improve oxygenation and lung mechanics during PCV > 0 due to asthma, emphysema, chronic bronchitis, and 41 © Jones & andBartlett PSV in patientsLearning, with ARDS.LLC The use of sigh breaths© JonesCOPD) & often Bartlett responds Learning, well to administration LLC of low to NOT FOR SALEwith PSV OR and DISTRIBUTION PCV has been investigated in an animal NOTmoderate FOR SALE concentrations OR DISTRIBUTION of oxygen (Fio2 0.30 to 0.50). model of mild lung injury, resulting in mixed results.41 Hypoxemia due to intrapulmonary shunt (e.g., ARDS, pneumonia, significant atelectasis, and pulmonary Effects of Mechanical edema) or diffusion defects may require much higher oxygen concentrations and the application of PEEP. Ventilation on Organ Systems © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Mechanical ventilationNOT effects FOR oxygenation, SALE OR ventilation, DISTRIBUTION RC Insights NOT FOR SALE OR DISTRIBUTION airway pressures, ventilatory muscles, work of breathing, the cardiovascular system, and other organ systems, Hypoxemia due to V˙ /Q˙ mismatch or hypoven-

as described below. tilation is suggested by a Pao2 increase of 4 to 5 mmHg for each 1% increase in oxygen percent- Pulmonary System © Jones & Bartlett Learning, LLC age; a < 5© mmHg Jones increase & Bartlett in Pao2 forLearning, each 10% in-LLC TheNOT primary FOR function SALE of aOR mechanical DISTRIBUTION ventilator is to crease in NOToxygen FOR percentage SALE suggests OR DISTRIBUTION the presence augment or replace normal ventilation and a primary in- of significant shunt. dication for initiation of mechanical ventilation is absent or inadequate spontaneous breathing. The goal of me- In general, the lowest necessary combinations of chanical ventilation is to support tissue oxygenation and PEEP and Fio2 should be used to maintain adequate © Jones & removalBartlett of carbonLearning, dioxide. LLC It is also important to note a © Jones & Bartlett Learning, LLC arterial oxygen partial pressures (Pao2) and O2 satura- NOT FOR SALEpatient’s OR baseline DISTRIBUTION status when setting specific oxygenationNOT FOR SALE OR DISTRIBUTION tions (Spo2 and Sao2). Respiratory care clinicians must and ventilation goals. For example, a patient who is apneic also keep in mind all the factors that affect tissue oxy- due to a drug overdose may otherwise have normal lungs. genation, which include arterial blood oxygen content This patient may require ventilatory support to achieve a (Cao2 = 1.34 × Hb × Sao2 + 0.003 × Pao2), oxygen normal Paco2, Pao2, and Sao2 using low to moderate con- ˙ = × ˙ © Jones & Bartlett Learning, LLCdelivery (Do2 Cao2 QT),© and Jones tissue oxygen & Bartlett uptake Learning, LLC centrations of oxygen. Oxygenation and ventilation goals and utilization. Attention to cardiac output, blood pres- for an acute exacerbationNOT of FORCOPD SALEin a patient OR who DISTRIBUTION is a sure, and peripheral perfusionNOT is important FOR SALE to ensure OR DISTRIBUTION retainer, however, would be different. This chronic CO2 adequate tissue oxygenation. patient’s baseline condition might be described as chronic The use of high concentrations of oxygen for pro- ventilatory failure and prior baseline arterial blood gases longed periods may cause oxygen toxicity. The toxic may indicate a compensated respiratory acidosis with effects of oxygen on the nervous system (e.g., tremors, mild© hypoxemia.Jones & VentilatingBartlett thisLearning, patient to achieveLLC a nor- © Jones & Bartlett Learning, LLC convulsions) are usually confined to patients receiv- malNOT Paco FORmay result SALE in an OR unwanted DISTRIBUTION alkalosis. NOT FOR SALE OR DISTRIBUTION 2 ing hyperbaric therapy. Breathing 100% oxygen at normal barometric pressure can damage the pulmo- Oxygenation nary capillary endothelium, resulting in interstitial Although they are related processes, it is sometimes edema and thickening of the alveolar capillary mem- © Jones & helpfulBartlett to consider Learning, ventilation LLC and oxygenation sepa- © Jonesbrane. & Continued Bartlett breathing Learning, of very LLC high concentra- NOT FOR SALErately. Fio OR2 and DISTRIBUTION PEEP are the primary tools used to NOTtions FOR of SALEoxygen mayOR then DISTRIBUTION cause alveolar type I cell achieve improvement in arterial oxygenation in venti- destruction and proliferation of alveolar type II cells. lated patients. Modern ventilators allow the clinician Alveolar fluid may ontinuec to accumulate resulting in

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© Jones &ventilation/perfusion Bartlett Learning, mismatch, LLC intrapulmonary shunt,© JonesVentilatory & Bartlett failure, Learning, or acute hypercapnic LLC respiratory and severe hypoxemia. Oxygen toxicity may then cul- NOTfailure, FOR isSALE a primary OR indication DISTRIBUTION for mechanical ventila- NOT FOR SALEminate inOR pulmonary DISTRIBUTION fibrosis. To avoid the development tion. The goal of mechanical ventilation in this case is of oxygen toxicity, most clinicians try to limit the use of to improve the patient’s alveolar ventilation, which is 100% oxygen to less than 24 hours. If an Fio2 of 1.0 is inversely related to Paco2 by the following equation: required, it has been suggested that the Fio2 be reduced ˙ ˙ VA = (VCO2 × 0.863)/Paco2, to 0.70 within 2 days© and Jones 0.50 or & less Bartlett within 5 days.Learning, Fio2 LLC © Jones & Bartlett Learning, LLC < ˙ ˙ 0.60 is not likely toNOT cause FOR oxygen SALE toxicity OR and DISTRIBUTIONFio2 where VA is alveolar ventilationNOT and FORVCO2 SALEis OR DISTRIBUTION of 0.50 or less is generally considered safe for extended CO2 production. periods. It should be noted, however, that Fio2 should As alveolar ventilation decreases, Paco2 increases not be reduced arbitrarily in the face of continuing se- and vice versa. Thus, clinically speaking the single vere hypoxemia. Other detrimental effects of breathing best index of alveolar ventilation is measurement of higher concentrations of oxygen include the develop- Paco2. That said, CO2 production can affect ventila- © Jones & Bartlett Learning, LLC © Jones & Bartlett˙ Learning, LLC ment of absorption atelectasis, depression of ventilation tory requirements. Normal VCO2 is about 200 mL/min; NOT FOR SALE OR DISTRIBUTION ˙ NOT FOR SALE OR DISTRIBUTION in some COPD patients with chronic hypercapnia (i.e. however, VCO2 varies directly with metabolic rate. For oxygen-associated hypercapnia), and retinopathy of pre- example, an increase in metabolic rate (e.g., fever, shiv- ˙ maturity in neonates. ering, and agitation) will increase VCO2 and, in turn, As discussed earlier, PEEP and CPAP are used ventilatory requirements. © Jones & toBartlett maximize Learning, alveolar recruitment LLC and prevent © Jones & Bartlett Learning, LLC NOT FOR SALEcycles of OR recruitment DISTRIBUTION and derecruitment in patients NOT FOR SALE OR DISTRIBUTION with acute restrictive pulmonary disease (e.g., ARDS). RC Insight The goal of PEEP is to improve surface area for gas exchange, while avoiding alveolar overdistention. Al- The single best index of effective alveolar venti- veolar overdistention may result in compression of lation in the clinical setting is measurement of pulmonary capillaries© andJones redistribution & Bartlett of pulmo Learning,- LLCPaco2. © Jones & Bartlett Learning, LLC nary blood flow resultingNOT inFOR increased SALE shunt. OR PEEPDISTRIBUTION NOT FOR SALE OR DISTRIBUTION also increases intrathoracic pressure, which may decrease venous return and has the potential to decrease With mechanical ventilation, V˙ and Paco can be cardiac output. A 2 altered by adjusting tidal volume, inspiratory pressure, The application of PEEP/CPAP for patients with inspiratory time, and respiratory rate, depending on acute restrictive pulmonary disease will often allow for © Jones & Bartlett Learning, LLC the mode employed.© Jones Normal & Bartlett adult spontaneous Learning, tidal LLC a reduction in the Fio required to achieve adequate ar- NOT FOR SALE2 OR DISTRIBUTION volume is approximatelyNOT FOR 5SALE to 7 mL/kg. OR DISTRIBUTIONOn mechanically terial oxygenation. Optimal PEEP should maximize oxy- ventilated patients, tidal volume may be initially set at gen delivery to the tissues. Other techniques that may 6 to 8 mL/kg PBW, calculated as follows: help oxygenation in ventilated patients include prone positioning (for ARDS patients), increased mean airway PBW (men) = [50 + 2.3 × height (in)] – 60 pressures (e.g., prolonged inspiratory times, inverse © Jones & Bartlett Learning, LLC © JonesPBW & Bartlett (women) =Learning, [45.5 + 2.3 ×LLC height (in)] – 60 ratio ventilation), alveolar recruitment maneuvers, se- NOT FOR SALEcretion managementOR DISTRIBUTION (e.g., suctioning and airway care), NOTWith FOR volume SALE ventilation, OR DISTRIBUTION the tidal volume is set directly. and administration of bronchodilators. Conservative With pressure ventilation, the pressure can be adjusted fluid management (to reduce pulmonary edema) and to achieve an initial VT of 6 to 8 mL/kg. A backup or treatment of fever, anxiety, and pain (to reduce oxygen mandatory respiratory rate is usually initiated in the consumption) may also© Jonesbe helpful. & Bartlett Learning, LLCrange of 12 to 14 breaths/min© if providingJones & assist-control Bartlett Learning, LLC ventilation. A higher rate may be used in cases of acute NOT FOR SALE OR DISTRIBUTIONhypercapnia, metabolic acidosis,NOT and FOR ARDS. SALE A lower OR rate DISTRIBUTION Ventilation may be used in exacerbations of obstructive lung dis- Mechanical ventilation can increase tidal volume, ease (e.g., asthma and COPD) to minimize air trapping. ˙ increase minute ventilation (VE), and decrease the Inspiratory time and I:E ratio are particularly important patient’s© Jones WOB. & Mechanical Bartlett Learning,ventilation with LLC positive in patients with© Jones obstructive & Bartlett lung disease. Learning, For a given LLC pressureNOT willFOR also SALE increase OR mean DISTRIBUTION airway pressure and respiratory NOTrate, a decreaseFOR SALE in inspiratory OR DISTRIBUTION time results in may increase mean intrathoracic pressure, reduce ve- an increase in expiratory time, which may be needed in nous return, and reduce cardiac output. Inspiratory these patients to avoid gas trapping and autoPEEP. mechanical bronchodilation occurs during positive When considering alterations in ventilation to achieve pressure breathing, which may increase pulmonary a desired Paco2, the clinician should always consider © Jones & deadBartlett space. Learning, Mechanical ventilationLLC also tends to in- © Jonesthe relationship & Bartlett between Learning, Paco2 and LLC pH. For example, a NOT FOR SALEcrease ventilation OR DISTRIBUTION to nondependent portions of the NOTpatient FOR maySALE rapidly OR trigger DISTRIBUTION the ventilator resulting in a lung and may reduce blood flow to nondependent por- lower Paco2 in compensation for a metabolic acidosis tions of the lung. (e.g., if pH = 7.20 expect Paco2 = 20 for compensation).

9781284139860_CH03_095_154.indd 143 21/02/19 5:37 PM 144 CHAPTER 3 Principles of Mechanical Ventilation

© Jones &If Bartlett the respiratory Learning, care clinician LLC adjusts the level of © JonesPulmonary & Bartlett barotrauma Learning, is caused LLC by alveolar rupture ventilatory support to increase the patient’s Paco2 to NOTdue FOR to elevated SALE transalveolarOR DISTRIBUTION pressures (the pressure NOT FOR SALE40 mmHg, OR the DISTRIBUTION patient’s pH will further decrease to about difference between alveoli and the adjacent interstitial 7.04, a life-threatening value. In general, pH will decrease space). Types of barotrauma include pneumothorax, acutely about 0.08 units for each 10-mmHg increase in mediastinum, pneumoperitoneum, and subcutaneous Paco2. On the other hand, a patient with COPD and emphysema. Barotrauma may be caused by excessive chronic CO2 retention© (i.e.,Jones chronic & Bartlettventilatory Learning,failure) LLCVT, elevated Pplateau, and PEEP.© Other Jones causes & Bartlettinclude Learning, LLC may have a baseline PaNOTco2 ofFOR 55 mmHg SALE resulting OR DISTRIBUTION in a chest trauma, thoracentesis, centralNOT FORline placement, SALE OR DISTRIBUTION normal or near-normal pH. If the patient is sedated and biopsy, thoracic surgery, manual ventilation, and im- the ventilator is adjusted to achieve a “normal” Paco2 of proper chest tube placement. 40 mmHg for this patient, an alkalosis will result. In the VC mode, decreased compliance or increased airway resistance will increase PIP, and improvements RC© JonesInsights & Bartlett Learning, LLC in compliance© Jonesor resistance & Bartlett will lower Learning, PIP. In general, LLC NOT FOR SALE OR DISTRIBUTION PIP should beNOT limited FOR to notSALE more OR than DISTRIBUTION 40 cm H2O, and P should be limited to less than 28 to 30 cm H O, For every acute change in Paco of 10 mmHg, pH plateau 2 2 to avoid ventilator-associated lung injury (VALI). Bron- will vary by 0.08 units. Thus, an acute increase in chospasm, mucosal edema, and secretions will increase Paco2 of 10 mmHg will result in a decrease in pH of airway resistance; suctioning, airway care, and adminis- 0.08. An acute decrease in Paco of 10 mmHg will © Jones & Bartlett Learning, LLC 2 © Jonestration & of Bartlett bronchodilators Learning, and anti-inflammatory LLC medi- result in an increase in pH of 0.08. NOT FOR SALE OR DISTRIBUTION NOTcations FOR maySALE be helpful. OR DISTRIBUTION Lung compliance may decrease due to worsening pneumonia, ARDS, or pulmonary edema, while the development of abdominal disten- Airway Pressures tion (e.g., ascites) may worsen thoracic compliance. Positive pressure ventilation increases peak and mean Attention to the specific cause of reduced compliance airway pressures, and© these Jones pressures & Bartlett are a function Learning, of LLCor increased resistance may result© Jones in lower & PIP.Bartlett Specific Learning, LLC the patient’s condition,NOT ventilatory FOR SALE mode employed, OR DISTRIBUTION and ventilator adjustments can alsoNOT reduce FOR PIP SALEduring vol-OR DISTRIBUTION ventilator settings. Higher peak and plateau inspiratory ume ventilation including lowering the set tidal volume, pressures (PIP, Pplateau) are associated with increased risk decreasing inspiratory peak flow, and change in the of lung injury, while increased mean airway pressures inspiratory flow waveform. For example, a down-ramp (Paw) reduce venous return and may reduce cardiac inspiratory flow waveform (aka decelerating flow) will output© Jones in hemodynamically & Bartlett unstableLearning, patients. LLC Increased tend to have© a Joneslower PIP & then Bartlett a square Learning, wave (although LLC PawNOT, however, FOR may SALE also improve OR DISTRIBUTION distribution of inspired a down-rampNOT will alsoFOR tend SALE to have OR an increasedDISTRIBUTION Paw as gases and arterial oxygenation. compared to a square wave). Ventilator-induced lung injury (VILI) is an With volume ventilation, mean airway pressure is af- acute lung injury (ALI) caused or made worse by me- fected by the tidal volume, inspiratory time, inspiratory chanical ventilation. VILI is characterized by increased flow waveform, respiratory rate, PIP, and PEEP. With © Jones & pulmonaryBartlett Learning,capillary permeability, LLC interstitial and al- © Jonesvolume & ventilation, Bartlett decreasedLearning, compliance LLC or increased veolar edema, alveolar hemorrhage, surfactant loss, and resistance will also increase PIP and Paw. With flow- NOT FOR SALEalveolar ORcollapse. DISTRIBUTION VILI is most commonly seen in ARDSNOT cycled FOR pressure-support SALE OR DISTRIBUTION ventilation or time-cycled, patients, although it may be seen with other conditions. pressure-control ventilation, increasing or decreasing Ventilator-associated lung injury (VALI) is a term inspiratory pressure will have a corresponding effect on used when it is not possible to determine if injury was mean airway pressure. The pressure pattern or pressure

due to the ventilator ©or otherJones factors & Bartlett (e.g., worsening Learning, LLCwaveform will also affect Paw©during Jones pressure-control & Bartlett Learning, LLC of the patient’s disease). VALI may be caused by volu- ventilation. For example, a square wave–like pressure trauma, atelectrauma,NOT or biotrauma. FOR SALE Lung injuryOR DISTRIBUTIONdue waveform will produce a descendingNOT FOR ramp SALEflow wave- OR DISTRIBUTION to alveolar overdistention is referred to as volutrauma, form (aka decelerating flow) and increased Paw. A more although it is difficult to separate the effects of volume linear or curvilinear increase in pressure (e.g., up-ramp from the associated pressures during mechanical ventila- pressure waveform) will produce a relatively lower Paw. tion.© CommonJones &causes Bartlett of volutrauma Learning, are excessive LLC tidal With time-cycled© Jones pressure-control & Bartlett ventilation, Learning, increas- LLC volumes,NOT elevatedFOR SALE Pplateau , ORand lungDISTRIBUTION overdistention due to ing inspiratoryNOT time FOR and reducingSALE OR expiratory DISTRIBUTION time will autoPEEP. Lung injury due to cyclic alveolar expansion also increase mean airway pressure and vice versa. and collapse is referred to as atelectrauma, as may be The addition of extrinsic PEEP or an increase in seen during mechanical ventilation of ARDS patients. PEEP will also increase mean airway pressure, while a Various open lung techniques and appropriate use of reduction in PEEP will reduce mean airway pressure. © Jones & PEEPBartlett have beenLearning, suggested LLC to avoid atelectotrauma. Lung© JonesThe effect & Bartlett of PEEP Learning, on Paw is direct; LLC for each 1-cm NOT FOR SALEinjury due OR to DISTRIBUTIONrelease of inflammatory mediators by in- NOTH FOR2O increase SALE in ORPEEP, DISTRIBUTION Paw will also increase by 1 cm jured lung tissue is sometimes referred to as biotrauma. H2O. AutoPEEP (aka intrinsic PEEP) is PEEP caused

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© Jones &inadvertently, Bartlett Learning, often due to LLC inadequate expiratory times© Jonesthe diaphragm. & Bartlett Acute Learning, restrictive lung LLC disease (e.g., in patients with obstructive lung disease; autoPEEP alsoNOT ARDS, FOR pneumonia)SALE OR stresses DISTRIBUTION the ventilatory muscles NOT FOR SALEincreases OR Paw DISTRIBUTION, although autoPEEP measurement re- and often leads to ventilatory muscle fatigue. Other quires the use of an end-inspiratory pause. causes of muscle weakness in ventilated patients include immobilization and the use of sedative, narcotic, Heterogeneous Ventilation and paralytic drugs; mechanical ventilation can be a Heterogeneous ventilation© Jones describes & Bartlett nonuniform Learning, dis- LLCcontributing factor. © Jones & Bartlett Learning, LLC tribution of inspiredNOT gas within FOR the SALE lung. This OR is DISTRIBUTION related Controlled mechanical ventilationNOT FOR occurs SALE when theOR DISTRIBUTION to regional lung compliance, airway resistance, and patient is apneic due to his or her medical condition dependency (upper versus lower lung zones). These (e.g., coma, head trauma, and massive stroke) or the use factors vary from region to region in the lung and thus of sedative or paralytic agents. With controlled venti- ventilation is heterogeneous. For example, in the nor- lation, the WOB is eliminated allowing for complete mal,© upright Jones lung, & Bartlettapical (nondependent) Learning, lung LLC units ventilatory muscle© Jones rest. &Controlled Bartlett ventilation Learning, often LLC re- tendNOT to receive FOR less SALE perfusion, OR whileDISTRIBUTION lung units at the quires the useNOT of sedative FOR SALEand neuromuscular OR DISTRIBUTION blocking bases tend to receive more perfusion because of grav- agents, which may jeopardize patient safety in the event ity. Better-ventilated areas include those that are more of a ventilator malfunction or disconnect. It should also compliant, nondependent, and have lower airway re- be noted that while neuromuscular blocking agents sistance. Conversely, poorly ventilated regions include paralyze the patient, they do not influence the patient’s © Jones & thoseBartlett that are Learning, less compliant, LLC dependent, and have © Jonesconsciousness & Bartlett or perception Learning, of pain LLC and discomfort. NOT FOR SALEhigher airway OR DISTRIBUTION resistance. While some degree of hetero-NOTThus, FOR neuromuscularSALE OR DISTRIBUTION blocking agents should not be geneity is always present, it is often more exaggerated in used without the addition of appropriate sedation and patients with airway and parenchymal lung disease. pain control. Further, respiratory muscle weakness and atrophy may occur in patients receiving extended peri- Ventilation/Perfusion Mismatch ods of controlled mechanical ventilation and the use of © Jones & Bartlett Learning, LLCneuromuscular blocking agents.© Jones Neuromuscular & Bartlett weak- Learning, LLC Mechanical ventilation may produce three differ- ness (e.g., critical illness myopathy and critical illness NOT FOR SALE˙ ˙ OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ent forms of ventilation/perfusion (V/Q) mismatch: polyneuropathy) is often seen in critically ill patients, ˙ > ˙ ˙ ˙ (1) ‑ventilation (V) perfusion (Q): high V/Q or dead and is associated with sepsis, multiorgan failure, and ˙ < ˙ ˙ ˙ < > ˙ ˙ = space; (2) V Q: V/Q 1 but 0; and (3), V/Q 0 – systemic inflammatory response syndrome. Ventila- shunt. During spontaneous ventilation, inspired gas is tory muscle weakness and dysfunction may prolong the primarily© Jones distributed & Bartlett to the dependentLearning, and LLC peripheral patient’s dependency© Jones on & mechanical Bartlett supportLearning, and cause LLC zones of the lungs. Conversely, when positive pressure NOT FOR SALE OR DISTRIBUTION weaning difficulty.NOT FOR IMV SALE allows forOR interspersing DISTRIBUTION manda- is applied, the inspired gas tends to be distributed to tory and spontaneous breathing and the provision of the nondependent lung zones. These nondependent partial ventilatory support. It is of interest to note that areas receive less perfusion resulting in ventilation of early advocates of IMV suggested that an advantage ˙ > ˙ poorly perfused areas (V Q) or increased dead space of this mode was maintenance of ventilatory muscle ventilation. Positive pressure may also compress the © Jones & Bartlett Learning, LLC © Jonesfunction & andBartlett avoidance Learning, of ventilatory LLC muscle atrophy. pulmonary capillaries leading to increased pulmonary Unfortunately, evidence has not shown IMV to be ben- NOT FOR SALEvascular OR resistance DISTRIBUTION and decreased pulmonary blood NOTeficial FOR in SALE this respect. OR DISTRIBUTION Newer modes of ventilation that flow to areas that are better ventilated. Perfusion is then allow patients to continue to utilize their ventilatory redirected to the dependent areas of the lung that are muscles while receiving mechanical ventilatory support ˙ ˙ less well ventilated (V/Q mismatch). If there is no ven- are available (see below). tilation of perfused areas (V˙/Q˙ = 0), then intrapulmonary shunt is created.© Jones & Bartlett Learning, LLCDiaphragmatic Dysfunction© Jones & Bartlett Learning, LLC Positive pressure ventilationNOT FOR may SALE reduce OR intrapulmo- DISTRIBUTIONVentilator-induced diaphragmaticNOT dysfunction FOR SALE can OR DISTRIBUTION nary shunt by improving alveolar ventilation and pre- develop within hours and worsens with the duration venting or reversing atelectasis, especially when PEEP is of mechanical ventilation.43 This may be related to applied. Positive pressure ventilation tends to increase increased oxidative stress on the diaphragm. Direct dead space ventilation, in part due to inspiratory me- measures of diaphragmatic function have been elusive. chanical© Jones bronchodilation & Bartlett of theLearning, conducting LLC airways. © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Maximal inspiratoryNOT FOR pressure SALE (MIP), OR respiratory DISTRIBUTION fre- Normal dead space to tidal volume ratio (VD/VT) is 0.30 quency, tidal volume, and transdiaphragmatic pressures with a normal range of 0.20 to 0.40; VD/VT during me- have all been used as surrogate measures of diaphrag- chanical ventilation may be 0.50 or higher. matic function; however, these are all nonspecific and effort dependent. Nevertheless, diaphragmatic weak- Respiratory Muscles © Jones & Bartlett Learning, LLC © Jonesness occurs & Bartlett with mechanical Learning, ventilation LLC and the optimal NOT FOR SALEGeneralized OR skeletalDISTRIBUTION muscle weakness frequently oc- NOTtherapeutic FOR SALE strategy OR to DISTRIBUTION avoid this development remains curs in critically ill ICU patients, and this may include unclear. It may be beneficial to allow ventilated patients

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© Jones &to Bartlett maintain Learning,some level of LLCspontaneous diaphragmatic © Jonesof secretions & Bartlett and development Learning, of ventilator-associatedLLC function as allowed by patient comfort and adequate NOTpneumonia. FOR SALE Adequate OR DISTRIBUTION humidification, suctioning, and NOT FOR SALEgas exchange. OR DISTRIBUTION Newer modes of mechanical ventilation, airway care should be routine in patients receiving me- including neurally adjusted ventilatory assist (NAVA), chanical ventilation. adaptive support ventilation (ASV), and pressure-support ventilation (PSV) in which some level of spontane- Immune System ous breathing continues© Jones may have & advantagesBartlett Learning,regarding LLCMechanical ventilation with positive© Jones pressure & Bartlett may influ- Learning, LLC maintenance of diaphragmaticNOT FOR function. SALE Inspiratory OR DISTRIBUTION ence the immune system. ForNOT example, FOR ARDS SALE patients OR DISTRIBUTION muscle strength training has been explored in difficult 44 receiving lung protective ventilation (small VT with to wean patients. higher PEEP) may have fewer circulating inflammatory mediators than those receiving large tidal volumes Work of Breathing with no PEEP. Ventilator-associated pneumonia (VAP) Properly© Jones applied, & mechanicalBartlett Learning, ventilation can LLC reduce or is a form of ©hospital-acquired Jones & Bartlett pneumonia Learning, that devel- LLC eliminateNOT theFOR patient’s SALE WOB. OR This DISTRIBUTION is especially impor- ops 48 hoursNOT or more FOR after SALE the initiation OR DISTRIBUTION of mechanical tant in patients with respiratory muscle fatigue. The ef- ventilation. Clinical findings often include a new or pro- fects of mechanical ventilation on WOB are dependent gressive lung infiltrate on imaging, fever, purulent spu- on mode employed, ventilator settings, and the patient’s tum, leukocytosis, and deteriorating oxygenation status. condition. Controlled ventilation eliminates the WOB, © Jones & allowingBartlett for Learning, ventilatory muscle LLC rest. As noted above, © JonesCardiovascular & Bartlett System Learning, LLC NOT FOR SALEcontrolled OR ventilation DISTRIBUTION may also promote the develop- NOTAndre FOR Cournand SALE OR was DISTRIBUTIONamong the first to publish data on ment of respiratory muscle weakness and atrophy. the effects of positive intrathoracic pressures on cardiac Assist-control ventilation allows the patient to trigger output.45 During spontaneous ventilation, intrapleural an inspiration and trigger work can be substantial with and intrathoracic pressures decrease on inspiration, re- inappropriate trigger sensitivity settings or in the pres- © Jones & Bartlett Learning, LLCsulting in an increase in the venous© Jones return & to Bartlett the heart. Learning, LLC ence of autoPEEP. IMV allows the patient to spontane- Strong spontaneous inspiratory efforts can enhance this ously breathe betweenNOT mandatory FOR SALEbreaths; ORhowever, DISTRIBUTION normal effect and increase theNOT stroke FOR volume SALE and carOR- DISTRIBUTION WOB can be substantial when the IMV rate is reduced diac output. When intrathoracic pressures are positive to one-half of that required for full ventilatory support. during mechanical ventilation, the right ventricular (RV) For example, an IMV rate to achieve full ventilatory preload may be reduced if high mean airway pressures support may be 12 breaths/min; when the mandatory © Jones & Bartlett Learning, LLC reduce the cross-sectional© Jones & Bartlettarea of the Learning,great vessels. TheLLC rate is reduced to 6 breaths/min, the patient’s WOB may right ventricular afterload is affected by lung volume and approachNOT FORthat of SALEunsupported OR DISTRIBUTIONspontaneous breathing. its influenceNOT on pulmonary FOR SALE vascular OR resistance DISTRIBUTION (PVR; Mode of ventilation can have a direct impact Figure 3-32). As inspired volume approaches total lung on WOB. As noted, IMV can provide partial ven- capacity (TLC), PVR is increased along with an increase tilatory support that increases the patient’s WOB. in RV afterload. The higher afterload will increase RV Patient-triggered modes (assist-control) can introduce stroke work index but will reduce left ventricular (LV) © Jones & significantBartlett Learning,trigger work. LLCWith pressure-support ven- © Jones & Bartlett Learning, LLC NOT FOR SALEtilation, ORincreasing DISTRIBUTION pressure will tend to decrease the NOT FOR SALE OR DISTRIBUTION WOB. With VC ventilation, inappropriate settings for inspiratory flow and inspiratory time may cause Total patient–ventilator asynchrony and increased WOB. Alveolar With any mode that incorporates a patient trigger and/ Extra-alveolar or spontaneous breathing© Jones (e.g., IMV & Bartlett or PSV), theLearning, pa- LLC sistance © Jones & Bartlett Learning, LLC tient’s spontaneous ventilatoryNOT FOR pattern SALE can ORbe in DISTRIBUTION oppo- NOT FOR SALE OR DISTRIBUTION sition with the ventilator settings. For example, a patient with rapid shallow spontaneous breathing may poorly tolerate assist-control modes of ventilation by trying to exhale during the inspiratory phase of the ventilator. At- tention© Jones to avoiding & Bartlett patient–ventilator Learning, asynchrony LLC is an © Jones & Bartlett Learning, LLC importantNOT FOR aspect SALE of ventilator OR DISTRIBUTIONmanagement to improve re vascular Pulmonary NOT FOR SALE OR DISTRIBUTION patient comfort and reduce the WOB. RV FRC TLC Mucociliary Motility Lung volume © Jones & MechanicalBartlett Learning, ventilation appears LLC to impair airway mu- © Jones & Bartlett Learning, LLC Figure 3-32 The Influence of Lung Volume on Pulmonary Vascular NOT FOR SALEcociliary OR motility, DISTRIBUTION although the mechanism remains NOT FOR SALE OR DISTRIBUTION unclear. This dysfunction likely contributes to retention Resistance.

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© Jones &preload. Bartlett The Learning, degree of influence LLC of intrathoracic pres- © Jonespressure, & Bartlettvenous return, Learning, and cardiac LLC output were to sure on both right and left heart function are dependentNOT blame FOR for SALE reduced OR renal DISTRIBUTION perfusion. There also may be a NOT FOR SALEon the transmural OR DISTRIBUTION pressure gradient across the walls of neurohumoral component to positive pressure ventila- the great vessels and myocardial walls. If the lungs are tion’s effect on renal function. Mechanical ventilation has relatively compliant, the transmural wall pressure is di- been shown to activate the renin-angiotensin-aldosterone rectly influenced by alveolar pressure and the potential system and increase sympathetic tone, which may lead to for a decrease in cardiac© Jones output, especially& Bartlett in hypovole Learning,- LLCdecreased urine production. © Jones & Bartlett Learning, LLC atrial natriuretic mic patients, is moreNOT pronounced. FOR SALEOn the otherOR DISTRIBUTIONhand, The effects of positive pressureNOT FORon SALE OR DISTRIBUTION if the lungs are relatively noncompliant, the transmural peptide (ANP) production is less than straightforward. wall pressure may not be readily influenced, and higher There is also a link between lung injury and renal func- pressures may not cause immediate reductions in ve- tion. Inflammatory cytokines resulting from or caus- nous return and cardiac output. ing ARDS may contribute to renal dysfunction. In © Jones & Bartlett Learning, LLC the ARDSNet© trial,Jones it was & notedBartlett using Learning, lung protective LLC strategies (including lower tidal volumes) resulted in a NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR46 DISTRIBUTION RC Insight reduced incidence of renal failure. Lung injury may precede renal impairment as systemic inflammation During positive pressure ventilation, alveolar, pleu- leads to end organ failure. ral, and intrathoracic pressures are increased and In summary, patients receiving mechanical ventila- © Jones & Bartlettvenous return Learning, to the right LLC heart is reduced during © Jonestory support & Bartlett may develop Learning, acute renal LLC failure, and this NOT FOR SALEinspiration OR DISTRIBUTION and returns towards baseline during NOTmay FOR be dueSALE to multiple OR DISTRIBUTION factors such as decreased renal exhalation (in the absence of PEEP). Higher pres- blood flow due to decreased cardiac output, release sures and higher PEEP levels may further impede of inflammatory mediators, humoral pathways, or in- venous return, and this may reduce cardiac output creased sympathetic tone. in compromised patients. © Jones & Bartlett Learning, LLCGastrointestinal System© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Gastrointestinal tract stress ulcers associated with In summary, positive pressure ventilation creates critical illness and mechanical ventilation can result in positive pleural and intrathoracic pressures that com- gastrointestinal bleeding. The incidence of esophagi- press the intrathoracic veins resulting in decreased ve- tis, diarrhea, gall bladder inflammation, and impaired nous return and may result in decreased left ventricular gastrointestinal motility may also increase with posi- output.© Jones Right ventricular & Bartlett output Learning, is also decreased LLC as © Jones & Bartlett Learning, LLC tive pressure ventilation, although it remains unclear alveolarNOT distention FOR SALE compresses OR DISTRIBUTION the pulmonary capillar- NOT FOR SALE OR DISTRIBUTION whether this is related to mechanical ventilation or ies resulting in increased pulmonary vascular resistance, critical illness in general. or right ventricular afterload. The degree of decrease in The splanchnic perfusion refers to the perfusion of right and left ventricular output correlates with increas- the abdominal gastrointestinal organs (e.g., intestines, ing amounts of positive pressure and/or PEEP. As posi- stomach, pancreas, liver, and spleen); positive pres- © Jones & tiveBartlett pressure Learning, increases, cardiac LLC output may decrease. © Jones & Bartlett Learning, LLC sure ventilation is associated with decreased splanch- These effects are exaggerated in patients with low chest NOT FOR SALE OR DISTRIBUTION NOTnic FOR perfusion SALE (Figure OR DISTRIBUTION3-33). There appears to be a wall compliance (as in kyphoscoliosis) or high lung dose-dependent decrease in splanchnic perfusion as compliance (as in emphysema). In healthy patients, the amount of positive pressure applied increases, espe- compensatory mechanisms, including increases in heart cially with PEEP.47 This may be due to decreased cardiac rate and systemic vascular resistance, maintain blood output that may occur with increasing amounts of posi- pressure. If compensatory© Jones mechanisms & Bartlett are inadequate, Learning, LLC © Jones & Bartlett Learning, LLC tive pressure. Paco2 may also influence gut perfusion. hypotension develops.NOT It must FOR be noted,SALE however, OR DISTRIBUTION that Specifically, hypercapnia canNOT cause FORreflex SALEsplanchnic OR DISTRIBUTION positive pressure ventilation may be beneficial in pa- vascular dilation that follows an initial vasoconstriction tients with left ventricular failure by reducing venous related to an increased sympathetic outflow associated return and decreasing left ventricular afterload. 48 with high Paco2. Modes of ventilation that accom- Renal© Jones System & Bartlett Learning, LLC modate spontaneous© Jones breathing & Bartlett may improveLearning, splanchnic LLC NOT FOR SALE OR DISTRIBUTION blood flow.NOT In a 2003 FOR animal SALE model OR study DISTRIBUTION on oleic acid It may come as a surprise to some, but mechanical ven- induced lung injury, Hering et al. compared APRV ventilation can impact renal function and is an independent tilation with and without spontaneous breathing inter- risk factor for the development of acute renal failure. spersed. In this animal study, there was an increase in There are numerous hypotheses that have been proposed gastrointestinal perfusion in the group with spontane- 49 © Jones & toBartlett explain this Learning, relationship, LLC however the mechanisms © Jonesous breathing & Bartlett efforts. Learning, The utilization LLC of lung protective NOT FOR SALEremain poorlyOR DISTRIBUTION understood. It was once thought that the NOTstrategies FOR SALE may also OR preserve DISTRIBUTION gut function and reduce negative effects of mechanical ventilation on intrathoracic mortality associated with end-organ failure.

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1. 0 to lower ICP, and this has been suggested in the past to © Jones & Bartlett Learning, LLC* © Jones & Bartlett Learning, LLC NOTtreat FOR patients SALE with OR severe DISTRIBUTION head trauma and/or cerebral NOT FOR SALE0.8 OR DISTRIBUTION edema. Unfortunately, hyperventilation may also cause cerebral ischemia and contribute to secondary brain 0.6 injury and is currently not recommended in the initial treatment of severe traumatic brain injury. Optimal ICP 0.4 management requires a multimodal approach combin-

Tissue blood flow blood Tissue ing symptoms, imaging, and other physiological param- 0.2 NOT FOR SALE OR DISTRIBUTION NOT FOR55,56 SALE OR DISTRIBUTION eters to an individualized treatment plan. 0.0 Anxiety, agitation, and pain are common in patients APRV APRV APRV receiving mechanical ventilatory support. There is a with without without spontaneous spontaneous spontaneous component of discomfort associated with the endo- © Jones &breathing Bartlett Learning,breathing LLCbreathing tracheal tube© and Jones a common & Bartlett patient responseLearning, is to LLC equal V equal P NOT FOR SALE OR DISTRIBUTIONE AW attempt to removeNOT FOR the source SALE of that OR discomfort DISTRIBUTION (i.e., Control self extubation). Many ICU procedures and activi- Induced lung injury ties may increase patients’ discomfort. These include * P < 0.05 blood sampling, suctioning and airway care, wound care, bathing, linen changes, and other diagnostic and © Jones & FigureBartlett 3-33 Learning, The Effects of Spontaneous LLC Ventilation on Splanchnic© Jonestherapeutic & Bartlett procedures. Learning, Patients mayLLC experience anger, NOT FOR SALEBlood Flow. OR DISTRIBUTION NOTfear, FOR pain, SALE and frustration; OR DISTRIBUTION explaining procedures and Data from Hering, R., Viehofer, A., Zinserling, J., Wrigge, H., Kreyer, S., Berg, A., Minor, T., providing reassurance may be helpful. Oversedation, Putensen, C. Effects of spontaneous breathing during airway pressure release ventilation on intestinal blood flow in experimental lung injury. Anesthesiology. 2003;99(5):1137–1144. however, may delay ventilator weaning and is associated with reduced spontaneous ventilatory drive, increased ventilator days, and higher costs.57 The appropriate use Central Nervous System of sedatives and analgesics continues to be a mainstay © Jones & Bartlett Learning, LLC 58 © Jones & Bartlett Learning, LLC Mechanical ventilationNOT can FORhave both SALE direct OR and DISTRIBUTION indi- of pain management. DevelopmentNOT FOR of ICU SALE delirium OR is DISTRIBUTION rect effects on the central nervous system. The most a common problem and steps to reduce delirium, and minimize hemodynamic and respiratory effects of seda- notable direct affect is increased ICP due to increased 59 intrathoracic pressures and reduced venous return. tive drugs, should be implemented. The mere presence of an endotracheal tube can cause Sleep coughing© Jones and gagging& Bartlett and increased Learning, intrathoracic LLC © Jones & Bartlett Learning, LLC pressuresNOT FORthat may SALE cause ORtransient DISTRIBUTION elevations in ICP. ICU patientsNOT often FOR suffer SALE from poor OR sleep DISTRIBUTION quality and Impedance of venous return during positive pressure disordered sleep. This is due to disease-related factors, breathing can lead to increased ICP and decreased ce- patient care activities causing arousal and awakening rebral perfusion pressure. In healthy patients, cerebral and environmental noise. Maintaining normal circa- autoregulation minimizes these effects by maintaining dian rhythms, limiting environmental noise, reducing © Jones & cerebralBartlett perfusion. Learning, However, LLC in patients with underly- © Jonesadministration & Bartlett of sedatives Learning, and hypnotics, LLC and taking NOT FOR SALEing cerebrovascular OR DISTRIBUTION compromise, such as head injuries NOTsteps FOR to SALEtreat or avoidOR DISTRIBUTION the development of delirium may or intracranial tumors, these autoregulatory mecha- be helpful. nisms may be defective. This subset of patients may Sleep disruption in the ICU and sleep fragmenta- benefit from ICP monitoring while receiving mechani- tion related to mechanical ventilation are difficult to cal ventilation. differentiate. Sleep disruption refers to a disrupted Ventilator settings© and Jones the resultant & Bartlett pH and Learning, Pco2 LLCsleep-wake cycle. Sleep fragmentation© Jones refers & Bartlett to repeti- Learning, LLC can also influence ICP.NOT The FOR influence SALE of OR pH andDISTRIBUTION Paco2 tive, short interruptions in sleep.NOT Pain FOR is a commonSALE OR DISTRIBUTION on cerebral vasculature have been investigated since cause of sleep fragmentation. Bright lights, noise, move- the works of Lambertson and colleagues in the 1960s. ment, and anything that distracts from a dark, quiet They concluded that rapid CO2 conversion to hydrogen environment can lead to sleep fragmentation and day- ions and the CSF pH was the basis of vascular diameter time fatigue. Secretions, bronchospasm, and patient– alterations© Jones and & control Bartlett of cerebral Learning, blood flow. LLC Low or ventilator asynchrony© Jones can & Bartlettalso awaken Learning, the patient. LLC highNOT pH resultedFOR SALE in vasodilation OR DISTRIBUTION and vasoconstriction, InappropriateNOT alarm FOR settings SALE can resultOR DISTRIBUTION in further sleep 50-52 respectively. Harder & Madden showed Pco2’s effect fragmentation. When sleep fragmentation is displaced on vascular constriction independent of pH, suggest- by sleep loss, daytime sleepiness is the result, which ing various potential mechanisms influencing cerebral may delay weaning from mechanical ventilation. His- 53,54 blood flow (CBF) and ICP. Decreased Pco2 is a torically, ICU staff have been aware of sleep disruption © Jones & cerebralBartlett vasoconstrictor Learning, whileLLC increased Pco2 is a cere-© Jonesand measures & Bartlett have beenLearning, employed LLC to improve sleep in NOT FOR SALEbral vasodilator. OR DISTRIBUTION Thus, hyperventilation can be used NOTmechanically FOR SALE ventilated OR DISTRIBUTION patients.

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Complications of Mechanical injury and necrosis, impaired oxygen delivery, and dif- © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning,60 LLC Ventilation NOTfuse FOR alveolar SALE damage. OR DISTRIBUTION The transpulmonary pressure, NOT FOR SALE OR DISTRIBUTION which is the difference between the plateau pressure The complications related to mechanical ventilation are and pleural pressure, determines the degree of alveolar numerous and include both pulmonary and extrapul- distention. As plateau pressure rises, so does the trans- monary organ systems. pulmonary pressure, which can result in “volutrauma,” © Jones & Bartlett Learning, LLCor lung injury related to high© lung Jones volumes. & BartlettBaro- Learning, LLC Pulmonary NOT FOR SALE OR DISTRIBUTIONtrauma refers to injuries causedNOT by highFOR ventilation SALE OR DISTRIBUTION The pulmonary complications attributed to me- pressure, resulting in alveolar rupture and release of chanical ventilation are comprehensively called gas. Clinically, this includes pneumothorax, pneumo- “ventilator-associated lung injury” or VALI. These mediastinum, pneumopericardium, and subcutaneous complications include airway complications, pneumo- emphysema. Pneumothorax can be life threatening, thorax,© Jones equipment & Bartlett failure, lung Learning, injury related LLC to the especially in© patients Jones on & ongoing Bartlett mechanical Learning, ventila- LLC applicationNOT FOR of pressure, SALE development OR DISTRIBUTION of ventilator asso- tion, due to NOTthe development FOR SALE of tension OR DISTRIBUTION pneumothorax. ciated pneumonia (VAP), and oxygen toxicity. Tension pneumothorax is a medical emergency that requires prompt recognition and management includ- Airway Complications ing needle decompression followed by tube thoracos- tomy. Pneumomediastinum, pneumopericardium, and Most airway complications are associated with the subcutaneous emphysema typically have less clinical © Jones & endotrachealBartlett Learning, tube (ETT) LLCitself. Laryngeal and tracheal © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOTconsequence; FOR SALE however, OR DISTRIBUTION close monitoring for develop- injuries (including laryngeal edema, vocal cord injury, ment of pneumothorax in patients with pneumome- and tracheal stenosis) are the most common complica- diastinum is prudent. Additionally, airway pressures tions described. These are secondary to the direct pres- should be minimized (if possible) to prevent further sure and inflammation induced by the ETT and inflated lung injury. Conversely, ventilation at low tidal volumes cuff. The purpose of© theJones ETT cuff& Bartlett is two-fold: Learning, (1) to seal LLCcan induce “atelectrauma,” the© repeated Jones collapse & Bartlett and Learning, LLC the airway for optimal delivery of mechanical ventila- NOT FOR SALE OR DISTRIBUTIONopening of the alveoli with eachNOT breath. FOR Unfortunately, SALE OR DISTRIBUTION tion and (2) to prevent aspiration and reduce incidence due to the heterogeneity of lung disease, particularly of VAP. This must be balanced with the potential for prevalent in ARDS, a given pressure can induce atel- tracheal mucosal ischemia and resultant granulation, ectrauma in regions with decreased compliance while fibrosis, and stenosis. These changes are often seen with causing volutrauma in regions with normal compliance. cuff© pressuresJones &exceeding Bartlett 30 Learning,cm H2O, thus itLLC is recom- Because of this,© Jones it is recommended & Bartlett that Learning, patients re- LLC mended that cuff pressures be monitored and main- NOT FOR SALE OR DISTRIBUTION ceive low tidalNOT volumes FOR (typically SALE 6OR to 8 DISTRIBUTION mL/kg IBW) to tained at 20 to 30 cm H2O. limit volutrauma, with an appropriate level of PEEP to minimize atelectrauma. Equipment Failure Present-day mechanical ventilators are equipped with Ventilator-Associated Pneumonia © Jones & numerousBartlett alarms Learning, to alert LLChealth care providers to © JonesAs noted & Bartlettabove, ventilator-associated Learning, LLC pneumonia (VAP) changes in pressures, volumes, and respiratory rate. NOT FOR SALE OR DISTRIBUTION NOTis FOR pneumonia SALE that OR develops DISTRIBUTION after 48 hours on me- These alarms allow for early troubleshooting and avoid- chanical ventilation. Intubated patients are particularly ance of adverse events. However, these safeguards may susceptible to the development of pneumonia because be rendered ineffective by ventilator malfunction or the protective mechanisms of the upper airway are power failure, which may contribute to the morbidity bypassed. Most cases of VAP are thought to be caused and mortality of mechanically© Jones ventilated & Bartlett patients. Learning, For LLCby microaspiration of secretions© Jones from the & oropharynx Bartlett Learning, LLC this reason, a manualNOT resuscitator FOR (oftenSALE referred OR DISTRIBUTION to as or upper gastrointestinal tract.NOT The FORventilator SALE circuit OR DISTRIBUTION an “ambu-bag”) with PEEP valve should be readily avail- itself provides an environment for bacterial growth and able at the bedside to assure continued ventilation and biofilm production. Notably, exchanging the ventila- oxygenation of the patient while the ventilator malfunc- tor circuit does not appear to decrease the incidence tion is assessed and rectified. of VAP. Most cases are polymicrobial, especially by © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Lung Injury Due to Pressure gram-negative organisms, although the frequency of NOT FOR SALE OR DISTRIBUTION isolation ofNOT methicillin-resistant FOR SALE strains OR DISTRIBUTION of Staphylococ- Ventilator-induced lung injury (VILI) refers to the dam- cus aureus are rising. Due to associated morbidity and age to the lung induced by the application of positive mortality, high cost, and changes in reimbursement pressure. Alveolar overdistention, the primary driver of strategies, prevention of VAP has become an area of VILI, is thought to induce biophysical and biochemi- extensive research. Many different interventions have © Jones & calBartlett changes Learning,that result in increasedLLC permeability of the © Jonesbeen studied & Bartlett to reduce Learning, VAP including LLC a variety of cuff NOT FOR SALEalveolar-capillary OR DISTRIBUTION membrane, pulmonary edema, cell NOTdesigns, FOR SALE subglottic OR suctioning, DISTRIBUTION chlorhexidine oral rinses,

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© Jones &and Bartlett gastric decontaminationLearning, LLC to name a few; however, © Joneswhich &compresses Bartlett intrathoracic Learning, veins LLC leading to de- no clear prevention strategy has been established. Nev-NOTcreased FOR SALEvenous return.OR DISTRIBUTION This results in the pooling of ve- NOT FOR SALEertheless, OR VAP DISTRIBUTION prevention strategies include avoiding nous blood in the extrathoracic vasculature, particularly invasive mechanical ventilation when possible, mini- within the abdominal viscera. Increased intrathoracic mizing time on mechanical ventilation by minimizing pressure is also transmitted to adjacent structures, sedation and implementing weaning protocols early, el- which can falsely elevate hemodynamic measurements, evating the head of bed© Jones to 30 to 45& degrees,Bartlett and Learning, removal LLCincluding central venous pressure© Jones (CVP) &and Bartlett pulmo- Learning, LLC of subglottic secretions.NOT Formation FOR SALE of VAP OR bundle DISTRIBUTION nary capillary wedge pressureNOT (PCWP). FOR The SALE magnitude OR DISTRIBUTION protocols implementing these strategies has been as- of elevation is dependent upon the compliance of the sociated with a significant reduction in the development lung and the amount of PEEP applied. of VAP. Renal Oxygen Toxicity © Jones & Bartlett Learning, LLC As mentioned© Jonesabove, positive & Bartlett pressure Learning, ventilation isLLC an HighNOT concentrations FOR SALE of inspired OR DISTRIBUTION oxygen can contribute independentNOT risk factor FOR for SALE the development OR DISTRIBUTION of acute to a wide range of lung injury, from mild tracheobron- renal failure in critically ill patients.62 The mechanism chitis to diffuse alveolar damage that is histologically is poorly understood, but thought to be related to he- indistinguishable from ARDS. Hyperoxia produces modynamic, neurohormonal, and biotrauma factors. reactive oxygen species that deplete the cell’s antioxi- The systemic hemodynamic effects of positive pressure © Jones & dantsBartlett and induces Learning, cellular LLC injury. Since the airway lining© Jonesventilation, & Bartlett as previously Learning, discussed, LLC decrease renal NOT FOR SALEand alveoli OR are DISTRIBUTION most exposed to inspired oxygen, they NOTblood FOR flow SALE thereby OR reducing DISTRIBUTION glomerular filtration rate are also most at risk for cellular injury. Clinical conse- and urine output.63 Positive pressure ventilation af- quences include absorption atelectasis, worsening hy- fects numerous neurohormonal pathways including the percapnia, and airway and parenchymal damage. High renin-angiotensin axis, nonosmotic vasopressin release, levels of inspired oxygen result in alveolar nitrogen and atrial natriuretic peptide (ANP) production. This washout and ultimately© Jones alveolar &closure, Bartlett or atelectasis. Learning, LLCseries of complex interactions© culminates Jones & in Bartlett a decrease Learning, LLC Hyperoxic hypercarbiaNOT results FOR from SALE the Haldane OR DISTRIBUTION effect in renal blood flow and GFR,NOT and fluidFOR retention SALE withOR DISTRIBUTION and increased dead space ventilation. The Haldane ef- resulting oliguria.64 Finally, positive pressure ventilation fect describes the affinity of hemoglobin for oxygen or activates the inflammatory cascade with the release of carbon dioxide. Increases in inspired oxygen leads to multiple pro-inflammatory cytokines including IL-6, rightward displacement of the CO2-hemoglobin dis- IL-8, and TNFα. These mediators contribute to the sociation© Jones curve & given Bartlett that oxyhemoglobin Learning, bindsLLC CO2 development© ofJones oxidative & stressBartlett and cellular Learning, apopto- LLC lessNOT avidly FOR than deoxyhemoglobin. SALE OR DISTRIBUTION There is an increase sis, which leadsNOT to FORfurther SALE decline ORin renal DISTRIBUTION blood flow in oxyhemoglobin with increased Fio2 resulting in in- and GFR. creased dissociation of CO2 from hemoglobin leading to increased serum CO2 levels. Airway erythema and CNS/Psychological edema can be seen in the large airways bronchoscopi- Cerebral blood flow (CBF) is proportional to cerebral © Jones & callyBartlett within Learning, 6 hours on oxygen LLC therapy, even without © Jones & Bartlett Learning, LLC 60 perfusion pressure (CPP), which is the difference be- NOT FOR SALEpositive ORpressure. DISTRIBUTION NOTtween FOR mean SALE arterial OR pressureDISTRIBUTION (MAP) and ICP. Thus, Parenchymal injury can also be seen, although it CPP (and CBF) decreases as MAP decreases and ICP remains unclear whether this is from oxygen therapy increases. Critically ill patients may have decreases in alone or secondary to VILI. Certain drugs, such as bleo- MAP due to shock, high PEEP, and high mean airway mycin (Blenoxane), may increase the sensitivity of the pressures. Elevations in ICP may be seen in traumatic lungs to oxygen therapy. The general goal should be to © Jones & Bartlett Learning, LLCbrain injury, cerebrovascular ©accident, Jones intracerebral & Bartlett Learning, LLC minimize Fio (particularly to < 0.60 if possible) and 2 NOT FOR SALE OR DISTRIBUTIONhemorrhage, and intracranialNOT tumors. FOR SALE OR DISTRIBUTION administer PEEP to minimize alveolar derecruitment. Cerebral autoregulation is the ability of the cerebral The role of antioxidants remains unclear. circulation to maintain CBF with wide changes in CPP Extrapulmonary Organ Systems by adjusting the cerebral vascular resistance. Cerebral © Jones & Bartlett Learning, LLC autoregulation© Jones is limited & by Bartlett the ability Learning, of the cerebral LLC Extrapulmonary complications of mechanical ventila- arterioles to constrict and dilate. In the normal healthy tionNOT may beFOR cardiac, SALE cardiovascular, OR DISTRIBUTION renal, neurologic, individual, NOTcerebral FOR autoregulation SALE OR can DISTRIBUTIONmaintain CBF neuromuscular, psychologic, or gastrointestinal. Me- with CPP of 60 to 150 mmHg. In chronically hyper- chanical ventilation may also have an input on the pa- tensive or critically ill patients, this adaptation is often tient’s immune system and nutritional status. compromised.

© Jones & Cardiac/CardiovascularBartlett Learning, LLC © JonesNeuromuscular & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION As discussed previously, the application of positive ICU acquired weakness is widely prevalent in pressure increases pleural and intrathoracic pressures, patients following ICU hospitalizations and can

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© Jones &manifest Bartlett in threeLearning, ways: polyneuropathy, LLC myopathy, © Jonesvolume & ventilation Bartlett andLearning, low PEEP haveLLC higher concen- and/or muscle atrophy. Definitive diagnosis is made trations of inflammatory mediators than patients who NOT FOR SALE OR DISTRIBUTION 46, 60 NOT FOR SALEby electrophysiology OR DISTRIBUTION testing. Motor and sensory nerves receive smaller tidal volumes and higher PEEP. are stimulated, and the resultant action potentials ana- This potent activation of the inflammatory cascade is lyzed for nerve injury, muscle injury, or a combination implicated in the pathogenesis of VILI and is thought of both. Critical illness polyneuropathy (CIP) is a sym- to be the basis for improved outcomes in low tidal metric, distal sensory-motor© Jones axonal & Bartlett polyneuropathy Learning, LLCvolume ventilation. © Jones & Bartlett Learning, LLC that affects motor (especiallyNOT FOR extremity SALE and OR respiratory DISTRIBUTION NOT FOR SALE OR DISTRIBUTION muscles), sensory, and autonomic nerves. Critical illness myopathy (CIM) results in extremity and respiratory muscle weakness; however, sensory function is Key Points preserved (unlike in CIP). Both may result in extremity ■■ The iron lung and chest cuirass are examples of nega- and respiratory muscle weakness and difficulty weaning © Jones & Bartlett Learning, LLC tive pressure© Jones ventilators; & Bartlett the iron lung Learning, saved many LLC from the ventilator. NOT FOR SALE OR DISTRIBUTION lives duringNOT the FORpolio epidemics.SALE OR DISTRIBUTION ■■ Patient-triggered, pressure-cycled ventilators Nutritional (e.g., Bird Mark 7) and flow-sensitive breathing Critical illness results in increased catabolism by means valves (e.g., Bennett PR-2) were based on technology of the inflammatory cascade. Providing adequate nutri- developed during World War II. © Jones & tionalBartlett support Learning, is often challenging LLC in the ICU. Excessive© Jones■■ Patient- & Bartlett or time-triggered Learning, volume LLC ventilators were NOT FOR SALEnutritional OR support DISTRIBUTION increases metabolic rate and in- NOT FORintroduced SALE in OR the lateDISTRIBUTION 1960s and allowed for precise creases ventilation requirement. Insufficient nutritional control of the patient’s tidal volume, respiratory rate, support can contribute to respiratory muscle catabolism and minute ventilation. ■■ ˙ and atrophy, resulting in increased risk of nosocomial VO2 is defined as the volume of oxygen taken up by pneumonia. Nutritional support is essential. A retro- the body per minute; normal resting V˙ O is about © Jones & Bartlett Learning, LLC © Jones & 2Bartlett Learning, LLC spective analysis of over 4000 patients showed that 250 mL O2/min. ■■ ˙ early enteral feedingNOT (within FOR 48 hours) SALE resulted OR inDISTRIBUTION a de- VCO2 is defined as the volumeNOT ofFOR carbon SALE dioxide OR DISTRIBUTION crease in ICU and hospital mortality.65 The EDEN study produced by the body per minute; normal resting ˙ showed no significant difference in outcomes (ventilator VCO2 is about 200 mL CO2/min. ■■ days, 60-day mortality, and infectious complications) Inspiratory time (TI) is defined as the time from the between patients who received trophic feeds and those beginning to the end of inspiration, including any receiving© Jones full feeds. & Bartlett66 Thus, theLearning, general consensus LLC of breath hold© Jones time. & Bartlett Learning, LLC ■■ nutritionalNOT FOR guidelines SALE is that OR enteral DISTRIBUTION nutrition should be ExpiratoryNOT time FOR (TE) is SALE the time OR from DISTRIBUTION the end of instituted within 24 to 48 hours of ICU admission. inspiration until the end of expiration and the beginning of the next breath. ■■ Gastrointestinal The total cycle time (Ttot) = TI + TE; Ttot = 60 ÷ respiratory rate (f). The effects of positive pressure ventilation on the © Jones & Bartlett Learning, LLC © Jones■■ Normal & Bartlett tidal volume Learning, (V ) is about LLC 7 mL/kg of gastrointestinal system are primarily secondary to T NOT FOR SALE OR DISTRIBUTION NOT FORPBW; V SALET varies OR with DISTRIBUTION size, gender, age, activity, and changes in cardiac output and the resulting splanchnic disease. hypoperfusion. This hypoperfusion leads to increases ■■ The dead space volume (V ) is the volume of inspired in splanchnic resistance that can culminate in gastric D gas that fills the conducting zone of the lung and any mucosal ischemia and stress ulcer formation. For this unperfused alveoli. reason, mechanical ventilation for more than 48 hours © Jones & Bartlett Learning, LLC■■ Alveolar ventilation per minute© Jones (V˙ ) is & tidal Bartlett Learning, LLC is considered an indication for stress ulcer prophy- A NOT FOR SALE OR DISTRIBUTIONvolume (VT) minus dead spaceNOT (V FORD) times SALE rate (f): OR DISTRIBUTION laxis. Agents used for stress ulcer prophylaxis include V˙ = (V – V ) × f. cytoprotective agents (i.e., sucralfate) or acid suppres- A T D ■■ During invasive positive pressure ventilation, the sion agents (i.e., histamine receptor 2 antagonists or airway must be sealed to deliver pressure, flow, and proton pump inhibitors). Mucosal breakdown may also volume; a cuffed endotracheal or tracheostomy tube increase risk of bacterial translocation from the gastro- © Jones & Bartlett Learning, LLC is commonly© Jones used to & accomplish Bartlett the Learning, seal (hence LLC the intestinal tract to the blood and result in nosocomial NOT FOR SALE OR DISTRIBUTION term invasiveNOT ventilation). FOR SALE OR DISTRIBUTION infection. Gastrointestinal motility is often impaired ■■ During noninvasive positive pressure ventilation, the in patients on positive pressure ventilation for un- airway must also be sealed to deliver pressure, flow, clear reasons. This may manifest as an intolerance to and volume. An oro or nasal mask interface is com- enteral feeding. monly used to accomplish the seal (hence the term © Jones & Bartlett Learning, LLC © Jonesnoninvasive & Bartlett ventilation). Learning, LLC Immune System NOT FOR SALE OR DISTRIBUTION NOT FOR■■ Peak SALEinspiratory OR pressure DISTRIBUTION (PIP) is the highest proxi- Positive pressure ventilation triggers activation of the mal airway pressure attained during the inspiratory inflammatory cascade. Patients who receive large tidal phase of mechanical ventilation.

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■■ ■■ © Jones & BartlettPlateau pressure Learning, (Pplateau LLC) is the pressure measured © JonesThe & trigger Bartlett variable Learning, is the method LLC by which inspira- during an inspiratory hold maneuver, typically 1 sec-NOT FORtion begins;SALE triggers OR DISTRIBUTION include time or patient effort (as NOT FOR SALEond or OR less DISTRIBUTION in duration. sensed by a pressure or flow change or a neural signal ■■ Extrinsic PEEP is intentionally applied to the airway with NAVA). at end expiration for therapeutic purposes. ■■ The cycle variable is the method by which inspiration ■■ AutoPEEP (aka intrinsic PEEP, occult PEEP) is unin- stops; cycle variables include volume, time, pressure, tended PEEP, usually© Jones caused by& airflowBartlett obstruction Learning, LLCand flow. © Jones & Bartlett Learning, LLC ■■ and/or inadequateNOT TE. It FORis also SALEknown asOR air trappingDISTRIBUTION In the volume-control mode,NOT VT FORis set, andSALE PIP willOR DISTRIBUTION or dynamic hyperinflation and is more common in vary with changes in compliance and resistance; in patients with obstructive lung disease. the pressure-control mode, inspiratory pressure is ■■ Continuous positive airway pressure (CPAP) de- set and VT will vary with changes in compliance and scribes spontaneous breathing at an elevated baseline resistance. ■■ pressure.© Jones & Bartlett Learning, LLC Spontaneous© Jones VT can &be Bartlettpressure supported Learning, to reduce LLC ■■ PEEPNOT and FOR CPAP SALE increase OR mean DISTRIBUTION airway pressure, work of breathingNOT FOR (WOB) SALE and compensateOR DISTRIBUTION for the increase functional residual capacity (FRC), and in- imposed WOB due to the artificial airway. crease the surface area for gas exchange. ■■ Assist-control ventilation (AC) is an older term ■■ Physiologic PEEP is a small amount of PEEP used to refer to time- or patient-triggered CMV. (3 to 5 cm H2O) used for most patients to prevent AC may be volume controlled (VC-CMV) or © Jones & Bartlettexpiratory Learning, alveolar collapse. LLC © Jonespressure & Bartlett controlled Learning, (PC-CMV). LLC ■■ ■■ NOT FOR SALEOne approachOR DISTRIBUTION to optimal PEEP adjusts the PEEP NOT FORSynchronized SALE OR intermittent DISTRIBUTION mandatory ventilation level for the best tissue oxygen delivery (D˙ O2). (SIMV) refers to IMV in which mandatory breaths ■■ Mean airway pressure (Paw) is affected by tidal may be patient or time triggered. volume, PIP, PEEP, autoPEEP, rate, inspiratory time, ■■ Mandatory minute ventilation (MMV) is a mode inspiratory flow and pressure waveforms, expiratory of ventilation in which the ventilator automatically ˙ time, I:E ratio, and© the Jones patient’s & respiratoryBartlett Learning,mechan- LLCmakes adjustments to assure© Jonesa minimum & Bartlettset VE. Learning, LLC ■■ ics (compliance [C]NOT and resistanceFOR SALE [Raw]). OR DISTRIBUTIONPressure-support ventilationNOT (PSV) FOR is a SALE OR DISTRIBUTION ■■ Input power refers to the power source used by the patient-triggered, flow-cycled form of pressure venti- ventilator to perform the required work; input power lation. PSV can be used as a standalone, spontaneous may be electric or pneumatic. form of breathing or in conjunction with IMV. ■■ Most modern critical care ventilators are micro- ■■ Airway pressure-release ventilation (APRV) is a dual ©processor Jones controlled & Bartlett and controlLearning, systems LLC may be CPAP mode© Jones of ventilation. & Bartlett Learning, LLC open loop or closed loop. ■■ Automatic tube compensation (ATC) is an auto- ■■ NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION For most ventilator patients, VT is initiated at 6 to mated form of pressure support designed to reduce 8 mL/kg of predicted or ideal body weight (PBW the work of breathing associated with endotracheal or IBW; the terms are often used interchangeably). tube resistance. ■■ Clinically, the best index of effective ventilation is ■■ Volume-assured pressure support (VAPS) or pres- measurement of Paco2. sure augmentation refers to a “within breath” form of © Jones & Bartlett■■ Learning, LLC © Jones & Bartlett Learning, LLC VT and respiratory rate (f) are adjusted to alter Paco2 volume-targeted pressure support. NOT FOR SALEand pH.OR DISTRIBUTION NOT FOR■■ Proportional SALE assistOR DISTRIBUTION ventilation (PAV) is an automated ■■ Fio2 and PEEP are adjusted to alter oxygenation form of ventilatory support that adjusts the level of (Pao2, Sao2). support provided based on the patient’s measured ■■ Pressure control (PC) and volume control (VC) are inspiratory flow, elastance, and resistance. ■■ the two primary control© Jones variables & Bartlett for invasive Learning, me- LLCPressure-regulated volume© control Jones (PRVC) & Bartlett automati- Learning, LLC chanical ventilation. cally varies pressure breath to breath to achieve a ■■ NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Mandatory breaths occur when the ventilator deliv- set VT. ers the same breath type with every breath. ■■ Automode automatically titrates the level of sup- ■■ Spontaneous breaths occur when the start and end of port provided between control and support modes, inspiration are determined by the patient, indepen- depending on the patient’s level of spontaneous dent of other ventilator settings. ventilation. ■■ © Jones & Bartlett Learning, LLC ■■ © Jones & Bartlett Learning, LLC NOTWith CMV, FOR all SALE breaths OR are mandatory;DISTRIBUTION with IMV AdaptiveNOT support FOR ventilation SALE (ASV) OR DISTRIBUTIONis another form mandatory breaths are interspersed with spontane- of closed-loop, automated ventilation that combines ous breaths. aspects of pressure support and pressure control. ■■ VC and PC may be combined with continuous man- ■■ Types of high-frequency ventilation (HFV) in- datory ventilation (CMV) or intermittent manda- clude high-frequency positive pressure ventilation © Jones & Bartletttory ventilation Learning, (IMV); LLC thus, the primary modes © Jones(HFPPV), & Bartlett high-frequency Learning, jet ventilation LLC (HFJV), NOT FOR SALEof mechanical OR DISTRIBUTION ventilation are VC-CMV, VC-IMV, NOT FORhigh-frequency SALE OR percussive DISTRIBUTION ventilation (HFPV), and PC-CMV, and PC-IMV. high-frequency oscillatory ventilation (HFOV).

9781284139860_CH03_095_154.indd 152 21/02/19 5:38 PM References 153

■■ High-frequency oscillatory ventilation (HFOV) uses 10. Atlas GM. A mathematical model of mean airway pressure based © Jones & Bartlett Learning, LLC © Jonesupon & positiveBartlett end-expiratory Learning, pressure, LLC I:E ratio, and plateau pres- much lower than normal VT and very high ventila- NOT FOR SALE OR DISTRIBUTION NOT FORsure. SALECardiovasc OR Eng . DISTRIBUTION2003;3(4):131–139. tory rates to maintain ventilation while lowering the 11. Smiths Medical. ParaPAC plus – transport ventilator. Available at risk of ventilator-induced lung injury (VILI). https://www.smiths-medical.com/products/ventilation/. Updated ■■ Neurally adjusted ventilatory assist (NAVA) uses the 2017. diaphragm’s electrical (EMG) signal to initiate and 12. Zoll Medical Corporation. Zoll EMV+ 731 series transport cycle the breath from I to E. A specially designed ventilators for the military. Available at https://www.zoll.com © Jones & Bartlett Learning, LLC/medical-products/ventilators/.© Updated Jones 2015. & Bartlett Learning, LLC nasogastric catheter must be correctly positioned for NOT FOR SALE OR DISTRIBUTION13. Convertino V, Grudic G, MulliganNOT J, MoultonFOR SALES. Estimation OR of DISTRIBUTION NAVA to function. individual-specific progression to impending cardiovascular insta- ■■ The inspiratory flow waveforms include square, as- bility using arterial waveforms. J Appl Physiol. 2013;115:1196–2013. cending, descending, and sinusoidal. 14. Chatburn R, El-Khatib M, Mireles-Cabodevila E. A taxonomy ■■ Mechanical ventilation alarms must be properly for mechanical ventilation: 10 fundamental maxims. Respir Care. 2014;59(11):1747–1763. adjusted© Jones to assure& Bartlett proper monitoringLearning, and LLC patient 15. Slutsky A©, Ranieri Jones V. Mechanical & Bartlett ventilation: Learning, Lessons from LLC the safety.NOT FOR SALE OR DISTRIBUTION ARDSNetNOT trial. Respir FOR Res .SALE 2000;1:73–77. OR DISTRIBUTION ■■ Active humidification during invasive mechanical 16. Gentile M. Cycling of the mechanical ventilator breath. Respir ventilation should be targeted at 33 to 44 mg/L at Care. 2011;56(1):52–57. inspired temperatures of 34º to 41ºC; risk of thermal 17. Du H, Amato M, Yamada Y. Automation of expiratory trigger > sensitivity in pressure support ventilation. Respir Care Clin North injury is increased at 41ºC. Am. 2001;7(3):503–517. ■■ © Jones & BartlettIncreases Learning, in mean airway LLC pressure (Paw) decrease © Jones18. Mireles & Bartlett-Cabodevila Learning, E, Hatipoglu, LLCU, Chatburn R. A ratio- NOT FOR SALEvenous OR return DISTRIBUTION and may reduce cardiac output. NOT FORnal frameworkSALE ORfor selecting DISTRIBUTION modes of ventilation. Respir Care. ■■ Respiratory muscle atrophy and ventilator-induced 2013;58(2):348–366. diaphragmatic dysfunction can develop in patients 19. ARDSNet. Mechanical ventilation protocol summary. Available at http://www.ardsnet.org/files/ventilator_protocol_2008-07.pdf. receiving mechanical ventilatory support. 20. Henderson WR, Griesdale DE, Dominelli P, Ronco R. Does ■■ Hazards and complications associated with mechani- prone positioning improve oxygenation and reduce mortality in cal ventilation include© Jones increased & BartlettICP, acute Learning,renal fail- LLCpatients with acute respiratory© distress Jones syndrome? & BartlettCan Respir Learning, J. LLC 2014;21(4):213–215. ure, and gastrointestinalNOT FORbleeding. SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ■■ Other hazards of mechanical ventilation include 21. Mancebo J, Fernandez R, Blanch L, et al. A multicenter trial of prolonged prone ventilation in severe acute respiratory distress ventilator-associated pneumonia (VAP), VILI, airway syndrome. Am J Respir Crit Care Med. 2006;173:1233–1239. complications, and the risk of ventilator failure or ac- 22. Guerin C, Reignier J, Richard J., et al. Prone positioning in severe cidental disconnect. acute respiratory distress syndrome. N Engl J Med. 2013;368: ■■ 2159–2168. ©Reduced Jones Pco &2 isBartlett a cerebral Learning, vasoconstrictor LLC while in- © Jones & Bartlett Learning, LLC 23. Blosser S. Airway pressure release ventilation (APRV) man- creased Pco2 is a cerebral vasodilator; this should be NOT FOR SALE OR DISTRIBUTION agement.NOT APRV FORFinal Exam. SALE Available OR at DISTRIBUTIONhttps://www.pdffiller considered when caring for with patients with head .com/101286566-aprvpdf-APRV-final-from-Sandy-Blosser-. trauma or traumatic brain injury. 24. Mireles-Cabodevila E, Kacmarek RM. Should airway pressure ■■ Sleep fragmentation can impact patient outcomes release ventilation be the primary mode in ARDS? Respir Care. and care should be taken to reduce sleep disruption. 2016;61(6):761–773. 25. Zhou Y, Jin X, Lv Y, et al. 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33. Maquet Getinge Group. Neurally adjusted ventilatory assist intestinal blood flow in experimental lung injury. Anesthesiology. © Jones & Bartlett(NAVA®): Learning, Personalized ventilation. LLC Available at https:\\www© Jones2003;99(5):1137–1144. & Bartlett Learning, LLC NOT FOR SALE.maquet.com/int/products/nava/. OR DISTRIBUTION Updated 2016. NOT50. FOR Lamber SALEtsen CJ, OR Semple DISTRIBUTION SJ, Smyth MG, Gelfand R. H+ and 34. Kallio M, Peltoniemi O, Anttila E, et al. Neurally adjusted venti- pCO2 as chemical factors in respiratory and cerebral circulatory latory assist (NAVA) in pediatric intensive care: A randomized control. J Appl Physiol. 1961;16:473–484. controlled trial. Pediatr Pulmonol. 2014;50(1):55–62. 51. Harper AM, Bell RA. The effect of metabolic acidosis and alkalo- 35. Tobin, MJ. Principles and Practice of Mechanical Ventilation. sis on the blood flow through the cerebral cortex. J Neurol Neuro- 2nd ed. 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Yoon S, Zuccarello M, Rapoport R. pCO2 and pH regulation of ©lem Jones of alarm &fatigue Bartlett with physiologic Learning, monitor LLCdevices: A com- cerebral blood© Jones flow. Front & Physiol Bartlett. 2012;3:1–8. Learning, LLC NOTprehensive FOR observational SALE studyOR of DISTRIBUTION consecutive intensive care unit 55. LeRoux PNOT. Intracranial FOR pressure SALE monitoring OR DISTRIBUTION and management. patients. PLOS. 2014;9(10):1–23. In: Laskowitz D, Grant G, eds. Translational Research in Trau- 39. Restrepo R, Hirst K, Wittnebel L, Wettstein R. Clinical practice matic Brain Injury. Boca Raton, FL: CRC Press/Taylor and Francis guideline: Transcutaneous monitoring of carbon dioxide and oxy- Group; 2016. gen. Respir Care. 2012;57(11):1955–1962. 56. Schirmer-Mikalsen K, Vik A, Skogvoll E, et al. Intracranial pres- 40. Restrepo R, Walsh B. Humidification during invasive and noninva- sure during pressure control and pressure-regulated volume © Jones & Bartlettsive mechanical Learning, ventilation: LLC 2012. Respir Care. 2012;57(5):782–788.© Jonescontrol & Bartlett ventilation inLearning, patients with traumatic LLC brain injury: A ran- 41. Moraes L, Santos CL, Santos RS, et al. Effects of sigh during domized crossover trial. Neurocrit Care. 2016;24(3):332–341. NOT FOR SALEpressure OR control DISTRIBUTION and pressure support ventilation in pulmoNOT- 57. FOR Liu L,SALE Wu A, Yang OR Y, et al.DISTRIBUTION Effects of propofol on respiratory drive nary and extrapulmonary mild acute lung injury. Crit Care. and patient-ventilator synchrony during pressure support venti- 2014;18:474(4):1–13. lation in postoperative patients: A prospective study. Chin Med J. 42. Patroniti N, Foti G, Cortinovis B, et al. Sigh improves gas exchange 2017;130(10):1155–1160. and lung volume in patients with acute respiratory distress syn- 58. Tate J, Dabbs A, Hoffman L, et al. Anxiety and agitation in mechan- drome undergoing pressure© Jones support & ventilation. BartlettAnesthesiology Learning,. LLCically ventilated patients. Qual ©Health Jones Res. 2012;22(2):157–173. & Bartlett Learning, LLC 2002;96(4):788–794. 59. Chlan L, Skaar D, Tracy M, et al. Safety and acceptability of 43. Levine S, Nguyen T,NOT Taylor N,FOR et al. RapidSALE disuse OR atrophy DISTRIBUTION of dia- patient-administered sedativesNOT during FOR mechanical SALE ventilation. OR DISTRIBUTION phragm fibers in mechanically ventilated humans. N Engl J Med. Am J Crit Care. 2017;26(4):288–296. 2008;358:1327–1335. 60. Slutsky AS. Ventilator-induced lung injury. N Engl J Med. 44. Martin D, Smith B, Gabrielli A. Mechanical ventilation, dia- 2014:979–980. doi: 10.1056/NEJMc1400293. phragm weakness and weaning: A rehabilitation perspective. 61. Sackner MA, Landa J, Hirsch J, Zapata A. Pulmonary effects of ©Respir Jones Physiol & Neurobiol Bartlett. 2013;189(2):377–383. Learning, LLC oxygen breathing.© Jones Ann Intern& Bartlett Med. 1975;82:40–43. Learning, LLC 45. Cournand A, Motley H, Werko L, Richards D Jr. Physiological 62. Vivino G, Antonelli M, Moro ML, et al. Risk factors for acute renal NOTstudies FOR on the effectsSALE of intermittentOR DISTRIBUTION positive pressure breathing failure inNOT trauma patients.FOR SALEIntens Care OR Med. DISTRIBUTION 1998;24(8):808–814. on cardiac output in man. Am J Physiol. 1948;152:162–174. 63. Jarnberg PO, de Vilotta ED, Eklund J, Granberg PO. Effects of 46. ARDSNet, Brower R, Matthay M, et al. Ventilation with lower positive end-expiratory pressure on renal function. Acta Anaes- tidal volumes as compared with traditional tidal volumes for thesiol Scand. 1978;22:508–514. acute lung injury and the acute respiratory distress syndrome. 64. Koyner JL, Murray PT. Mechanical ventilation and lung–kidney N Engl J Med. 2000;342(18):1301–1308. interactions. J Am Soc Nephrol. 2008;3:562–570. doi:10.2215/CJN © Jones & 47.Bartlett Beyer J, ConzenLearning, P, Schosser LLC R, Messmer K. The effect of PEEP© Jones.03090707. & Bartlett Learning, LLC NOT FOR SALEventilation OR DISTRIBUTIONon hemodynamics and regional blood flow withNOT 65. FOR Artinian SALE V, Krayem OR H, DISTRIBUTION DiGiovine B. Effects of early enteral feed- special regard to coronary blood flow. Thorac Cardiovasc Surg. ing on the outcome of critically ill mechanically ventilated medi- 1980;28(2):128–132. cal patients. Chest. 2006;129(4):960–967. doi:129.960-07.10.1378 48. Fujita Y, Sakai T, Ohsumi A, Takaori M. Effects of hypocapnia /chest.129.4.960. and hypercapnia on splanchnic circulation and hepatic function 66. Rice TW, Wheeler AP, Thompson BT, et al. Initial trophic vs in the beagle. Anesth Analg. 1989;69(2):152–157. full enteral feeding in patients with acute lung injury: the EDEN 49. Hering R, Viehofer ©A, JonesZinserling &J, et Bartlett al. Effects Learning,of spontane- LLCrandomized trial. JAMA. 2012;307(8):795-803.© Jones & doi:10.1001/jama Bartlett Learning, LLC ous breathing duringNOT airway FOR pressure SALE release OR ventilation DISTRIBUTION on .2012.137. NOT FOR SALE OR DISTRIBUTION

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