Mechanical Ventilation © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT for SALE OR DISTRIBUTION NOT for SALE OR DISTRIBUTION

CHAPTER © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 22 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Mechanical Ventilation © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Dean R. Hess Neil© R.Jones MacIntyre & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION OUTLINE patient–ventilator proportional assist asynchrony ventilation (PAV) The Equation of Motion peak inspiratory spontaneous breathing Indications for Mechanical Ventilation pressure (PIP) trial (SBT) Complications of Mechanical Ventilation permissive hypercapnia synchronized © Jones & VentilatorBartlett Settings Learning, LLC © Jones & Bartlett Learning, LLC plateau pressure intermittent mandatory NOT FOR SALEMonitoring OR the DISTRIBUTION Mechanically Ventilated Patient NOT FOR SALE OR DISTRIBUTION positive end-expiratory ventilation (SIMV) Choosing Ventilator Settings for Different Forms of pressure (PEEP) transpulmonary pressure Respiratory Failure pressure control ventilator-induced lung Ventilatory Support Involves Trade-Offs ventilation (PCV) injury (VILI) Liberation from Mechanical Ventilation © Jones & Bartlett Learning, LLCpressure support ©volume Jones control & Bartlett Learning, LLC OBJECTIVES NOT FOR SALE OR DISTRIBUTION ventilation (PSV) NOT ventilation FOR (VCV)SALE OR DISTRIBUTION pressure triggering weaning parameters 1. List the indications for and complications of mechanical ventilation. INTRODUCTION 2. Discuss issues related to ventilator-associated Mechanical ventilation is an important life support © Joneslung injury. & Bartlett Learning, LLC technology ©that Jones is an integral & Bartlett component Learning, of critical LLC 3.NOT Select FOR appr SALEopriate ORventilator DISTRIBUTION settings. care. MechanicalNOT ventilationFOR SALE can beOR applied DISTRIBUTION as nega- 4. List parameters that should be monitored during tive pressure to the outside of the thorax (e.g., the mechanical ventilation. iron lung) or, most often, as positive pressure to the 5. Discuss issues related to liberation from airway. The desired effect of positive pressure ventila- mechanical ventilation. tion is to maintain adequate levels of PaO2 and PaCO2 © Jones & KEYBartlett TERMS Learning, LLC © Joneswhile also& Bartlett unloading Learning, the inspiratory LLC muscles. Mechani- cal ventilation is a life-sustaining technology, but rec- NOT FOR SALEadaptive OR pressure DISTRIBUTION high-frequency NOT FOR SALE OR DISTRIBUTION ognition is growing that when used incorrectly, it can control oscillatory ventilation increase morbidity and mortality. Positive pressure adaptive support (HFOV) ventilation is provided in intensive care units (ICUs), ventilation (ASV) intermittent mandatory subacute facilities, long-term care facilities, and the airway pressure release ventilation home. Positive pressure ventilation can be invasive ventilation (APRV) © Joneslung-protective & Bartlett ventilatorLearning, LLC © Jones & Bartlett Learning, LLC (i.e., with an endotracheal tube or tracheostomy tube) auto-PEEP NOT FOR strategy SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION or noninvasive (e.g., with a face mask). This chapter compressible volume mean airway pressure – addresses invasive positive pressure ventilation as continuous mandatory (Paw) it is applied in adults with acute respiratory failure. ventilation (CMV) neurally adjusted Modern ventilators used in the intensive care unit are continuous positive ventilatory assist microprocessor controlled and available from several airway© Jones pressure & Bartlett (CPAP) Learning, (NAVA) LLC © Jones & Bartlett Learning, LLC manufacturers (Figure 22–1 and Figure 22–2). flowNOT triggering FOR SALE OR oxygenDISTRIBUTION toxicity NOT FOR SALE OR DISTRIBUTION

462

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© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC FIGURENOT 22–1 FOR Examples SALE of mechanicalOR DISTRIBUTION ventilators commonly used in critical care in theNOT United States.FOR SALE OR DISTRIBUTION

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The Equation of Motion Expiratory valve © Jones & Bartlett Learning, LLC © Jones &(PEEP) Bartlett Learning, LLC Positive pressure, when applied at the air- NOT FOR SALE OR DISTRIBUTION AtmosphereNOT FOR SALE OR DISTRIBUTION way opening, interacts with respiratory system (lung and chest wall) compliance, Filter airways resistance, respiratory system inertance, and tissue resistance to produce gas flow into the lung.© InertanceJones &and Bartlett tissue ElectricalLearning, LLCMicroprocessor © JonesMonitors & Bartlett Learning, LLC Patient resistance are smallNOT and their FOR effects SALE are ORpower DISTRIBUTION(mode and breath delivery) NOTand alarmsFOR SALE OR DISTRIBUTION usually ignored. The interactions of airway pressure (Paw), respiratory muscle pressure (Pmus), flow, and volume with respi- Filter ratory system mechanics can be expressed Air

as the© Jonesequation & of Bartlettmotion: Learning, LLC O2 © Jones & Bartlett Learning, LLC Humidiﬁer PawNOT ϩ Pmus FOR ϭ (FlowSALE ϫ Resistance)OR DISTRIBUTION Inspiratory NOTvalve(s) FOR SALE OR DISTRIBUTION (ﬂow, volume, pressure, FIO ) ϩ (Volume/Compliance) 2 FIGURE 22–2 Modern ventilators are electronically and pneumatically controlled. The

For spontaneous breathing, Paw ϭ 0 and inspiratory valves control flow, pressure, and FIO2 to the patient. The expiratory valve all of the pressure required for ventilation is closed during the inspiratory phase and the inspiratory valve is closed during the © Jones & isBartlett provided Learning,by the respiratory LLC muscles. For expiratory phase.© Jones The expiratory & Bartlett valve controls Learning, positive end-expiratory LLC pressure (PEEP). ϭ The inspiratory and expiratory valves are controlled by the microprocessor. Sensors NOT FOR SALEfull ventilatory OR DISTRIBUTION support, Pmus 0 and all measure pressureNOT and FOR flow, whichSALE are displayedOR DISTRIBUTION as numeric and graphic data and of the pressure required for ventilation determine when an alarm condition is generated. is provided by the ventilator. For partial ventilatory support, both the ventilator and the respiratory muscles contribute to ventilation. © Jones & Bartlett Learning, LLC BOX 22–1© Jones & Bartlett Learning, LLC For full ventilatoryNOT support, FOR the SALE ventilator OR DISTRIBUTIONcontrols NOT FOR SALE OR DISTRIBUTION either the pressure or the flow and volume applied Indications for Mechanical to the airway. The equation of motion predicts that Ventilation Paw will vary for a given resistance and compliance if flow and volume are controlled (volume-targeted Apnea ventilation).© Jones The & Bartlettequation of Learning, motion also LLC predicts that Acute© Jones ventilatory & Bartlett failure (e.g., Learning, LLC rising Paco with acidosis, flowNOT and FORvolume SALE will vary OR for DISTRIBUTION a given resistance and NOT FOR SALE2 OR DISTRIBUTION compliance if Paw is controlled (pressure-targeted respiratory muscle dysfunc- ventilation). tion, excessive ventilatory An important point to remember in considering the load, altered central ventila- equation of motion is that in the setting of high minute tory drive) © Jones & ventilation,Bartlett Learning,long inspiratory-to-expiratory LLC time ratios,© Jones & BartlettImpending Learning, ventilatory LLCfailure Severe oxygenation deficit NOT FOR SALEand prolonged OR DISTRIBUTION expiratory time constants (e.g., as seen inNOT FOR SALE OR DISTRIBUTION obstructive lung disease), the lungs may not return to the baseline circuit pressure during exhalation. This creates auto-PEEP, which must be counteracted by Pmus and Paw in the equation of motion to affect flow and volume delivery. © Jones & Bartlett Learning, LLCfrom drug overdose or from© anesthesia Jones & involved Bartlett with Learning, LLC NOT FOR SALE OR DISTRIBUTIONmajor surgery is an indicationNOT that FOR does SALE not involve OR DISTRIBUTION Indications for Mechanical primary respiratory system failure. In short, mechanical ventilation is required when the patient’s capabilities to Ventilation ventilate the lung and/or effect gas transport across the Mechanical ventilation is indicated in many situations alveolocapillary interface is compromised to the point (Box© 22–1Jones).1 Goals & Bartlett of mechanical Learning, ventilation LLC are shown that the patient’s© Jones life is threatened.& Bartlett Learning, LLC in NOTBox 22–2 FOR. Although SALE ORthese DISTRIBUTION conditions are useful in NOT FOR SALE OR DISTRIBUTION the determination of whether mechanical ventilation Complications of Mechanical is needed, clinical judgment is as important as strict adherence to absolute guidelines. One indication for Ventilation mechanical ventilation is imminent acute respiratory Mechanical ventilation is not a benign therapy, and © Jones & failure;Bartlett in such Learning, cases, initiating LLC mechanical ventilation© Jonesit can &have Bartlett major effectsLearning, on the LLC body’s homeostasis NOT FOR SALEmay prevent OR DISTRIBUTIONovert respiratory failure and respiratoryNOT ( BoxFOR 22–3 SALE).2 In ORaddition DISTRIBUTION to the serious complications arrest. On the other hand, depression of respiratory drive reviewed here associated with positive pressure applied

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to the lungs,3 intubated mechanically ventilated patients bleeding5 and often are given antacids, proton pump © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC also are at risk for complications associated with the use inhibitors, or histamine (H2) blockers to prevent this NOT FOR SALEof artificial OR airways, DISTRIBUTION4 the most serious being accidentalNOT complication. FOR SALE The OR nutritional DISTRIBUTION needs of mechanically disconnection and the development of pneumonia from ventilated patients play an important role in preventing compromised natural airway defenses. Mechanically or promoting complications.6 Undernourished patients ventilated patients are also at risk for gastrointestinal are at risk for respiratory muscle weakness and pneumo- © Jones & Bartlett Learning, LLCnia. An excessive caloric intake,© Jones on the other & Bartlett hand, may Learning, LLC increase carbon dioxide (CO2) production, which can BOXNOT 22–2 FOR SALE OR DISTRIBUTIONmarkedly increase the patient’sNOT ventilatory FOR requirements.SALE OR DISTRIBUTION Sleep deprivation in mechanically ventilated patients has Goals of Mechanical Ventilation recently become recognized.7 Provide adequate oxygenation © JonesProvide & Bartlett adequate alveolarLearning, LLC Ventilator-Induced© Jones Lung& Bartlett Injury Learning, LLC NOT FORventilation SALE OR DISTRIBUTION The applicationNOT of FOR positive SALE pressure OR to DISTRIBUTION the airways can Avoid alveolar overdistension create lung injury under a variety of circumstances. Maintain alveolar recruitment Pulmonary barotrauma (e.g., subcutaneous emphy- Promote patient–ventilator sema, pneumothorax, pneumomediastinum) is one of synchrony the most serious complications of excessive pressure © Jones & Bartlett AvoidLearning, auto-PEEP LLC © Jonesand volume & Bartlett delivery Learning, to the lung and LLC is a consequence of NOT FOR SALE ORUse DISTRIBUTION the lowest possible Fio2 NOTalveolar FOR SALE overdistention OR DISTRIBUTION When choosing appropriate goals to the point of rupture RESPIRATORY RECAP of mechanical ventilation for (Figure 22–3).3 How- Types of Ventilator-Induced an individual patient, consider ever, even when the lung Lung Injury the risk of ventilator-induced is not distended to the » Volutrauma lung injury© Jones. & Bartlett Learning, LLCpoint of rupture, exces- © Jones» Atelectrauma & Bartlett Learning, LLC sive transpulmonary » Biotrauma NOT FOR SALE OR DISTRIBUTION NOT OxygenFOR toxicitySALE OR DISTRIBUTION stretching pressures »

Airway Complications Cardiovascular Complications Laryngeal edema Reduced venous return © Jones & Bartlett TrachealLearning, mucosal LLC trauma © JonesReduced & Bartlett cardiac Learning, output LLC NOT FOR SALE ORContamination DISTRIBUTION of the lower respiratory tractNOT FORHypotension SALE OR DISTRIBUTION Loss of humidifying function of the upper Gastrointestinal and Nutritional airway Complications Mechanical Complications Gastrointestinal bleeding Accidental disconnection Malnutrition Leaks in the© Jonesventilator & circuit Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Renal Complications Loss of electricalNOT FOR power SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Loss of gas pressure Reduced urine output Increase in antidiuretic hormone (ADH) and Pulmonary Complications decrease in atrial natriuretic peptide (ANP) Ventilator-induced lung injury Neuromuscular Complications Barotrauma © Jones & Bartlett Learning, LLC Sleep deprivation© Jones & Bartlett Learning, LLC NOT FOROxygen SALE toxicity OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Atelectasis Increased intracranial pressure Nosocomial pneumonia Critical illness weakness Inflammation Acid–Base Complications Auto-PEEP Respiratory acidosis © Jones & Bartlett AsynchronyLearning, LLC © JonesRespiratory & Bartlett alkalosis Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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beyond the normal maximum (i.e., 30 to 35 cm H O) Importantly, this approach may require acceptance of © Jones & Bartlett Learning, LLC 2 © Jones & Bartlett Learning, LLC can produce a parenchymal lung injury not associated less than normal values for pH and Pao2 in exchange for NOT FOR SALEwith extra-alveolar OR DISTRIBUTION air (ventilator-induced lung injuryNOT lower FOR (and SALE safer) OR distending DISTRIBUTION pressures. [VILI]).8 Importantly, it is the physical stretching and dis- VILI also can result from the cyclical opening of an tention of alveolar structures that causes the injury. This alveolus during inhalation and closure during exhalation concept has been demonstrated in numerous animal (cyclical atelectasis producing atelectrauma).14,15 Indeed, models in which limiting alveolar expansion (e.g., with pressures at the junction between an open and a closed © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning,16 LLC chest strapping) prevents lung injury even in the face of alveolus may exceed 100 cm H2O during this process. very high applied airwayNOT pressures. FOR SALE8 OR DISTRIBUTIONThis injury is reduced with theNOT use FOR of smaller SALE tidal OR vol- DISTRIBUTION Clinical trials have confirmed these animal observa- umes and may be ameliorated by optimal lung recruit- tions and indicate that ventilator strategies exposing ment and an expiratory pressure that prevents alveolar injured human lungs to transpulmonary pressures derecruitment. Positive end-expiratory pressure (PEEP), in excess of 30 to 35 cm H O are associated with lung however, can be a two-edged sword. If an increase in © Jones & Bartlett2 Learning, LLC © Jones & Bartlett Learning, LLC injury.9–12 Of note is that this injury may be more than PEEP results in an increase in alveolar recruitment, simplyNOT the FOR result SALE of excessive OR DISTRIBUTION end-inspiratory alveo- then the stressNOT (distribution FOR SALE of pressure)OR DISTRIBUTION in the lungs lar stretch. Excessive tidal stretch (i.e., repetitive tidal is reduced. If, on the other hand, an increase in PEEP volumes greater than 9 mL/kg), even in the setting of increases end-inspiratory transpulmonary pressure, then

maximal transpulmonary pressures less than 30 cm H2O, the strain (change in size of the lungs during inflation) 9,10,13 17 © Jones & mayBartlett contribute Learning, to VILI. LLC This provides the rationale© Joneson the & lungs Bartlett is increased. Learning, Other LLC ventilatory pattern for using lung-protective ventilator strategies that limit factors may also be involved in the development of VILI. NOT FOR SALEtidal volume OR DISTRIBUTIONand end-inspiratory distending pressures.NOT These FOR include SALE frequency OR DISTRIBUTION of stretch18 and the acceleration or velocity of stretch.19 Vascular pressure elevations may also contribute to VILI.20 VILI is manifest pathologically as diffuse alveolar 7,8,15 © Jones & Bartlett Learning, LLCdamage, and it increases© inflammatoryJones & Bartlett cytokines Learning, LLC in the lungs (biotrauma).21–24 VILI is also associated NOT FOR SALE OR DISTRIBUTIONwith systemic cytokine releaseNOT and FOR bacterial SALE transloca- OR DISTRIBUTION tion24 that are implicated in the systemic inflammatory response with multiorgan dysfunction that increases mortality. The way in which the lungs are ventilated © Jones & Bartlett Learning, LLC may therefore© Jones play a &role Bartlett in systemic Learning, inflammation LLC (Figure 22–4). NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Oxygen Toxicity Oxygen concentrations approaching 100% are known to FIGURE 22–3 Computed tomography scan of the thorax cause oxidant injuries in airways and lung parenchyma.25 of a mechanically ventilated patient with severe barotrauma. Much of the data supporting the concept of oxygen toxic- © Jones & BartlettNote the pr Learning,esence of pneumothorax, LLC pneumomediastinum, © Jones & Bartlett Learning, LLC ity, however, have come from animals that often have quite NOT FOR SALEand subcutaneous OR DISTRIBUTION emphysema. NOT FOR SALE OR DISTRIBUTION different tolerances to oxygen than humans. It is unclear what the safe oxygen concentration or MODS duration of exposure is in sick humans, such as those with acute lung injury (ALI) or acute respiratory distress syn- Biochemical© InjuryJones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC drome (ARDS). Many authorities have Cytokines, complement,NOT FOR SALE OR DISTRIBUTIONDistal Organs NOT FOR SALE OR DISTRIBUTION prostanoids, leukotrienes, argued that a fraction of inspired oxygen – Tissue injury secondary to reactive oxygen species, Bacteria inﬂammatory mediators cells (Fio2) less than 0.4 is safe for prolonged proteases – Impaired oxygen delivery periods of time and that a Fio2 greater Mechanical – Bacteremia than 0.80 should be avoided. However, ventilation© Jones & Bartlett Learning, LLC © JonesVILI &may Bartlett be more Learning, important clini-LLC Neutrophils NOT FORBiophysical SALE InjuryOR DISTRIBUTION NOT callyFOR than SALE oxygen OR toxicity. DISTRIBUTION In one large – Shear – Alveolar–capillary permeability study (ARDSnet), survival was greater – Overdistention – Cardiac output in patients with ALI/ARDS who were – Cyclic stretch – Organ perfusion – Intrathoracic pressure ventilated with a lower tidal volume, presumably avoiding significant VILI, FIGURE 22–4 Mechanical ventilation can result in biochemical and biophysical injury to despite the fact that the required Fio © Jones & theBartlett lungs, which Learning, may result in multisystem LLC organ failure. MODS, multiple© Jones organ dysfunction & Bartlett Learning, LLC 2 NOT FOR SALEsyndrome. OR Adapted DISTRIBUTION from Slutsky AS, Trembly L. Multiple system organNOT failure: FOR is mechanical SALE ORwas DISTRIBUTIONhigher in the group receiving the ventilation a contributing factor? Am J Respir Crit Care Med. 1998;157:1721–1725. lower tidal volumes.

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Ventilator-Associated Pneumonia As intrathoracic pressure increases with positive © Jones & Bartlett Learning, LLC © Jonespressure & Bartlettventilation, Learning, right ventricular LLC filling decreases NOT FOR SALEThe natural OR laryngeal DISTRIBUTION mechanism that protects the lowerNOT FOR SALE OR DISTRIBUTION respiratory tract from aspiration is compromised by an and cardiac output decreases. This is the rationale for endotracheal tube. This permits oropharyngeal debris using volume repletion to maintain cardiac output in to leak into the airways. The endotracheal tube also the setting of high intrathoracic pressure. The effect of impairs the cough reflex and serves as a potential portal reduced cardiac filling on cardiac output may be par- for pathogens to enter© theJones lungs. & The Bartlett underlying Learning, disease LLCtially counteracted by better left© Jonesventricular & functionBartlett due Learning, LLC process makes the lungs prone to infection. Finally, heavy to elevated intrathoracic pressures, which reduce left NOT FOR SALE OR DISTRIBUTION 33 NOT FOR SALE OR DISTRIBUTION antibiotic use in the ICU and the presence of very sick ventricular afterload. In patients with left heart failure, the reduced cardiac fill- patients in close proximity to each other are risk factors RESPIRATORY RECAP for antibiotic-resistant infection. ing and reduced left ven- Preventing ventilator-associated pneumonia (VAP) tricular afterload effects Indications for and of elevated intrathoracic Complications of Mechanical is important© Jones because & Bartlett it is associatedLearning, with LLC morbidity © Jones & BartlettVentilation Learning, LLC 26 pressure may actually and mortality. VAP prevention has become an impor- » Mechanical ventilation NOT FOR SALE OR DISTRIBUTION 26–29 improve cardiacNOT FORfunc- SALE OR DISTRIBUTION tant priority in the mechanically ventilated patient. is indicated to support Hand washing, elevating the head of the bed, and care- tion such that intratho- oxygenation and ventilation fully choosing antibiotic regimens can have important racic pressure removal of patients with acute preventive effects. Circuit changes only when vis- may produce left ven- respiratory failure. » A number of complications © Jones & iblyBartlett contaminated Learning, appear LLC to be helpful.30 Endotracheal© Jonestricular & failure Bartlett if positive Learning, LLC pressure ventilation is are possible with mechanical tubes that provide continuous drainage of subglottic ventilation, and efforts must NOT FOR SALE OR DISTRIBUTION NOT FOR SALE34 OR DISTRIBUTION secretions, endotracheal tubes with specialized cuff removed. be made to minimize these designs, and endotracheal tubes made with antimicro- Intrathoracic pres- conditions. bial materials are other ways of reducing lung contami- sure can also influence nation with oropharyngeal material. However, these distribution of perfusion, as described by the West model tubes are more expensive© Jones and their & Bartlett cost-effectiveness Learning, is LLCof pulmonary perfusion. In© the Jones supine & human Bartlett lung, Learning, LLC 31 blood flow is greatest in zone 3. As intra-alveolar pres- controversial. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION sure rises, there is an increase in zone 2 and zone 1 (deadи и space) regions, creating high ventilation-perfusion (V/Q) Auto-PEEP units. Dyspnea, anxiety, and discomfort associated with Auto-PEEP (also known as intrinsic PEEP or air trap- inadequate ventilatory support can lead to stress-related ping)© Jonesis the result & Bartlettof the lungs Learning, not returning LLC to the base- catecholamine© Jones release, & with Bartlett increases Learning, in myocardial LLC oxygen demands and risk of dysrhythmias.34 In addition, lineNOT proximal FOR airway SALE pressure OR DISTRIBUTION at end-exhalation. The NOT FOR SALE OR DISTRIBUTION determinants of auto-PEEP are high minute volume, coronary blood vessel oxygen delivery can be compro- long inspiratory-to-expiratory time relationships, and mised by inadequate gas exchange from the lung injury long expiratory time constants (i.e., obstructed airways coupled with low mixed venous Po2 due to high oxygen and high-compliance alveolar units). Auto-PEEP raises consumption demands by the inspiratory muscles. © Jones & allBartlett intrathoracic Learning, pressures, LLC which can affect gas delivery,© Jones & Bartlett Learning, LLC hemodynamics, end-inspiratory distention (and thus Ventilator Settings NOT FOR SALEVILI), and OR patient DISTRIBUTION breath triggering. Although some-NOT FOR SALE OR DISTRIBUTION times desired in long inspiratory time ventilatory strate- Volume Control Versus Pressure Control gies, auto-PEEP is generally to be avoided because it is With volume control ventilation (VCV), the ventila- difficult to recognize and to predict its effects. tor controls the inspiratory flow (Figure 22–5). The © Jones & Bartlett Learning, LLCtidal volume is deter- © Jones & Bartlett Learning, LLC mined by the flow and Hemodynamic EffectsNOT FORof Positive SALE OR DISTRIBUTION NOTRESPIRATORY FOR SALE RECAP OR DISTRIBUTION the inspiratory time. In Pressure Ventilation Volume Control Versus practice, however, the Pressure Control Ventilation Because positive pressure ventilation increases intratho- flow and tidal volume » Volume control: Ventilation racic pressure, it can reduce venous return, which may are set on the ventila- remains constant with result© Jones in decreased & Bartlett cardiac output Learning, and a drop LLC in arterial tor. With VCV© Jones the tidal & Bartlettchanges Learning, in respiratory LLC bloodNOT pressure. FOR SALEFluid administration OR DISTRIBUTION and drug therapy volume isNOT delivered FOR SALE ORmechanics, DISTRIBUTION but airway (such as with vasopressors and inotropes) may be nec- regardless of resistance and plateau pressures can fluctuate. essary to maintain cardiac output, blood pressure, and or compliance, and the » Pressure control: Ventilation urine output under these circumstances. Mechanical peak airway pressure fluctuates with changes in ventilation also can cause an increase in plasma antidi- varies (Box 22–4). VCV respiratory mechanics, but © Jones & ureticBartlett hormone Learning, (ADH) andLLC a decrease in atrial natri-© Jonesshould & be Bartlett used when- Learning, LLCpressure is limited to the uretic peptide (ANP), which may reduce urine output ever a constant tidal vol- peak pressure set on the NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONventilator. and promote fluid retention.32 ume is important in the

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maintenance of a desired Paco2, such as with an acute ramp. A descending ramp flow pattern produces a longer © Jones &head Bartlett injury. Learning, The principal LLC disadvantage of VCV is that© Jonesinspiratory & Bartlett time unless Learning, the peak flow LLC is increased. NOT FOR SALEit can produce OR DISTRIBUTION a high peak alveolar pressure and areas ofNOT FORWith SALE pressure OR DISTRIBUTIONcontrol ventilation (PCV) overdistention in the lungs. Also, because the inspiratory (Figure 22–6), the airway pressure is set and remains flow is fixed, VCV can cause patient–ventilator asyn- constant despite changes in resistance and compliance. chrony, particularly if the inspiratory flow is set too low. Box 22–5 lists factors that affect the tidal volume with With VCV, the set flow© Jones can be constant & Bartlett or a descending Learning, LLCPCV. The principal advantage© of Jones PCV is &that Bartlett it prevents Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

NOT FOR SALEFlow (L/min) –80 OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 2 4 6 8 10 12 14 O)

2 50 © Jones & Bartlett Learning,40 LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION30 NOT FOR SALE OR DISTRIBUTION 20 10 0

Pressure (cm H Pressure 2 4 6 8 10 12 14 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 800 600NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 400 200

Volume (mL) Volume 0 © Jones & Bartlett Learning,2 LLC4 6 8 © 10Jones &12 Bartlett 14 Learning, LLC NOT FOR SALE(A) OR DISTRIBUTION Time (s) NOT FOR SALE OR DISTRIBUTION

) 40

L/min 0 ( –40 © Jones & Bartlett Learning,Flow LLC © Jones & Bartlett Learning, LLC –80 NOT FOR SALE OR DISTRIBUTION 2 4 NOT6 FOR8 SALE10 OR DISTRIBUTION12 14

O) 2 50 40 cm H ( ©30 Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 20 NOT10 FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 0 Pressure Pressure 2 4 6 8 10 12 14

800 © Jones & Bartlett) Learning, LLC © Jones & Bartlett Learning, LLC

mL 600 ( NOT FOR SALE400 OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 200 Volume Volume 0 2 4 6 8 10 12 14 © Jones & Bartlett Learning,(B) LLC ©Time Jones (s) & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONFIGURE 22–5 (A) Constant-flow (square wave) NOTvolume controlFOR ventilation. SALE (ORB) Descending DISTRIBUTION ramp-flow volume control ventilation.

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localized alveolar overdistention with changes in resis- improve patient–ventilator synchrony.35,36 The choice © Jones &tance Bartlett and compliance; Learning, the LLC peak alveolar pressure can-© Jonesof VCV & Bartlettor PCV often Learning, is determined LLC by clinician or NOT FOR SALEnot be greaterOR DISTRIBUTION than the pressure set on the ventilator.NOT institutional FOR SALE bias, OR and DISTRIBUTION both modes have advantages and Because the flow can vary with PCV, this mode may disadvantages (Table 22–1).37

BOX© Jones 22–4 & Bartlett Learning, LLC BOX 22–5© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Factors That Affect Tidal Volume (VT) Factors That Affect Peak with Pressure Control Ventilation Inspiratory Pressure (PIP) with Volume Control Ventilation Driving pressure: A higher driving pressure (difference between peak inspi- Peak inspiratory flow setting: A © Jones & Bartlett Learning, LLC © ratoryJones pressure & Bartlett and PEEP) Learning, increases LLC higher flow setting increases NOT FOR SALE OR DISTRIBUTION NOTthe Vt.FOR SALE OR DISTRIBUTION the PIP. Auto-PEEP: An increase in auto-PEEP Inspiratory flow pattern: PIP is reduces the Vt. lower with descending ramp Inspiratory time: An increase in inspira- flow. tory time increases the Vt if inspi- © Jones & Bartlett PositiveLearning, end-expiratory LLC pressure © Jones & Bartlett Learning, LLC ratory flow is present; after flow (PEEP): An increase in PEEP NOT FOR SALE OR DISTRIBUTION NOT FOR SALEdecreases OR DISTRIBUTION to zero, further increases in increases the PIP. the time do not affect the Vt. Auto-PEEP: Auto-PEEP increases Compliance: Decreased compliance the PIP. decreases the Vt. Tidal volume (Vt): An increase in Resistance: Increased resistance Vt results© Jones in a higher & Bartlett PIP. Learning, LLC © Jones & Bartlett Learning, LLC decreases the Vt; after flow decreases Resistance: Greater airways resis- NOT FOR SALE OR DISTRIBUTION to zero, resistanceNOT no FORlonger SALEaffects OR DISTRIBUTION tance results in a higher PIP. the delivered Vt. Compliance: Decreased compli- Patient effort: Greater inspiratory effort ance results in a higher PIP. by the patient increases the Vt. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

) 40

L/min 0 ( © Jones & Bartlett Learning,–40 LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONFlow NOT FOR SALE OR DISTRIBUTION –80 2 4 6 8 10 12 14

O) 2 50 ©40 Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC cm H ( NOT30 FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 20 10 0 Pressure Pressure 2 4 6 8 10 12 14 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC

800 NOT FOR SALE) OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

mL 600 ( 400 200 Volume Volume 0 © Jones & Bartlett Learning, LLC 2 4 ©6 Jones 8& Bartlett10 Learning,12 LLC14 NOT FOR SALE OR DISTRIBUTION NOTTime FOR (s) SALE OR DISTRIBUTION FIGURE 22–6 Pressure control ventilation.

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Ventilator Mode Pressure support ventilation (PSV) (Figure 22–9) is © Jones & Bartlett Learning, LLC © Jonesa spontaneous & Bartlett breathing Learning, mode in LLCwhich patient effort is NOT FOR SALEOptions OR for breathDISTRIBUTION delivery are referred to as modesNOT FOR SALE OR DISTRIBUTION of ventilation.38–41 Traditional modes include continu- augmented by a clinician-determined level of pressure 42 ous mandatory ventila- during inspiration. Although the clinician sets the level of pressure support, the patient sets the respiratory rate, RESPIRATORY RECAP tion (CMV), also called assist/control (A/C), inspiratory flow, and inspiratory time. The Vt is deter- Ventilator Modes © Jones synchronized& Bartlett Learning,intermit- LLCmined by the level of pressure© Jonessupport, &the Bartlett amount ofLearning, LLC » Continuous mandatory patient effort, and the resistance and compliance of the ventilation (CMV) tent mandatory ven- NOT FOR SALE OR DISTRIBUTIONpatient’s respiratory system. NOT FOR SALE OR DISTRIBUTION » Synchronized intermittent tilation (SIMV), and mandatory ventilation (SIMV) pressure support venti- » Pressure support ventilation lation (PSV). The choice (PSV) ■ TABLE 22–1 Advantages and Disadvantages of Volume of mode often is based Control and Pressure Control Ventilation » Continuous positive airway on institutional policy pressure© Jones (CPAP) & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC or the clinician’s bias. Type Advantages Disadvantages » AdaptiveNOT pressure FOR SALEcontrol OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION (APC) No one mode is clearly Volume Constant tidal Increased plateau » Adaptive support ventilation superior; each has its control volume (VT) pressure (Pplat) (ASV) advantages and disad- ventilation with changes in with decreasing » Airway pressure release vantages (Table 22–2). resistance and compliance (alveolar compliance overdistention) ventilation (APRV) Continuous manda- © Jones & Bartlett Learning, LLC © Jones & BartlettType of Learning, ventilation LLCFixed inspiratory » Tube compensation (TC) tory ventilation (CMV) NOT FOR» SALEProportional OR assist DISTRIBUTION ventilation NOT FOR SALE ORfamiliar DISTRIBUTION to most flow may cause (PAV) (or assist/control ven- clinicians asynchrony Neurally adjusted ventilatory tilation) delivers a set » Pressure Reduced risk of Changes in VT with assist (NAVA) volume or pressure and control overdistention changes in resistance » High-frequency oscillatory a minimum respiratory ventilation with changes in and compliance ventilation (HFOV) © Jones rate& Bartlett (Figure 22–7 Learning,). The LLC compliance. © JonesLess familiar & Bartlett type of Learning, LLC NOT FORpatient SALE can OR trigger DISTRIBUTION addi- Variable flow NOT FORventilation SALE for most OR DISTRIBUTION tional breaths above the minimum rate, but the set improves clinicians synchrony in volume or pressure remains constant. When mechani- some patients cal ventilation is begun, it often is best to use CMV (assist/control) to produce nearly complete respiratory muscle rest (i.e., full ventila-

© Jones & Bartlett Learning, 60 LLC © Jones & Bartlett Learning, LLC ) toryNOT support). FOR Regardless SALE OR of the DISTRIBUTION 40 NOT FOR SALE OR DISTRIBUTION mode used, the goal is to strike 20 L/min a balance between excessive ( 0 –20 respiratory muscle rest, which Flow –40 promotes atrophy, and exces- –60 © Jones & siveBartlett respiratory Learning, muscle LLC activ- 2 © Jones4 & Bartlett6 Learning,8 10LLC 12 14 NOT FOR SALEity, which OR promotes DISTRIBUTION fatigue—or, NOT FOR SALE OR DISTRIBUTION put more simply, to avoid the O) 24 2 extremes of too much rest and 20 16 cm H too much exercise. ( 12 Patient-triggered Ventilator-triggered breath breath Continuous positive airway 8 pressure (CPAP) is© a Jones sponta- & Bartlett4 Learning, LLC © Jones & Bartlett Learning, LLC 0 neous breathing mode (Fig- Pressure NOT FOR SALE OR DISTRIBUTION2 4 6 8 NOT10 FOR SALE12 OR14 DISTRIBUTION ure 22–8). The airway pressure is usually but not necessarily 600

greater than atmospheric pres- ) 500 mL

sure. CPAP is commonly used as ( 400 a means© Jones of maintaining & Bartlett alveolar Learning, 300 LLC © Jones & Bartlett Learning, LLC recruitment in mild to moder- 200

NOT FOR SALE OR DISTRIBUTION Volume 100 NOT FOR SALE OR DISTRIBUTION ate forms of pulmonary edema 0 and parenchymal lung injury. 2 4 6 8 10 12 14 CPAP often is used to evaluate a Time (s) patient’s ability to breathe spon- FIGURE 22–7 Continuous mandatory ventilation illustrating ventilator-triggered and patient- © Jones & taneouslyBartlett before Learning, extubation. LLC triggered breaths. © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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Pressure support ventilation is a frequently used cycle to the expiratory phase without the need for active © Jones &mode Bartlett of mechanical Learning, ventilation. LLC However, because it is© Jonesexhalation. & Bartlett Learning, LLC NOT FOR SALEpatient triggered,OR DISTRIBUTION PSV is not an appropriate mode forNOT FORThe flowSALE at which OR DISTRIBUTIONthe ventilator cycles to the expira- patients who do not have an adequate respiratory drive. tory phase during PSV can be a fixed absolute flow, a PSV normally is flow cycled, with secondary cycling flow based on the peak inspiratory flow, or a flow based mechanisms of pressure and time. Although PSV often on peak inspiratory flow and elapsed inspiratory time. is considered a simple© Jones mode of & ventilation, Bartlett Learning,it can be LLCSeveral studies have reported© asynchronyJones & Bartlettwith PSV inLearning, LLC quite complex (Figure 22–10). First, the ventilator must individuals with airflow obstruction, such as chronic recognize the patient’sNOT inspiratory FOR SALEeffort, which OR DISTRIBUTIONdepends obstructive pulmonary diseaseNOT (COPD). FOR43,44 SALE With airflow OR DISTRIBUTION on the ventilator’s trigger sensitivity and the amount obstruction, the inspiratory flow decreases slowly during of auto-PEEP. Second, the ventilator must deliver an PSV, and the flow necessary to cycle may not be reached; appropriate flow at the onset of inspiration. A flow that this course of action stimulates active exhalation to pres- is too© Joneshigh can &produce Bartlett a pressure Learning, overshoot, LLC and a flow sure cycle the© breath.Jones The & problemBartlett increases Learning, with higher LLC that is too low can result in patient flow starvation and levels of PSV and with higher levels of airflow obstruc- asynchrony.NOT FOR Third, SALE the ventilatorOR DISTRIBUTION must appropriately tion. On newerNOT ventilators, FOR SALE the ORtermination DISTRIBUTION flow can

■ TABLE 22–2 Advantages and Disadvantages of Common Modes of Mechanical Ventilation © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Mode of Ventilation Advantages Disadvantages NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Continuous mandatory ventilation Guaranteed volume (or pressure) with each High mean airway pressure (CMV) breath Respiratory alkalosis and auto-PEEP if patient Low patient workload if sensitivity and triggers at rapid rate inspiratory flow set correctly Respiratory muscle atrophy possible

Synchronized intermittent© mandatoryJones & LowerBartlett mean airway Learning, pressure LLC Asynchrony if rate ©set Jonestoo low & Bartlett Learning, LLC ventilation (SIMV) NOT FOR SALEPrevents respiratoryOR DISTRIBUTION muscle atrophy High work of breathingNOT with FOR older ventilators SALE OR DISTRIBUTION Pressure support ventilation (PSV) Variable flow may improve synchrony in some Requires spontaneous respiratory effort patients Fatigue and tachypnea with PSV too low Overcomes tube resistance Activation of expiratory muscles with PSV too high Prevents respiratory muscle atrophy © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Adaptive pressure control Ventilator maintains tidal volume with changes Does not precisely control tidal volume NOT FOR SALE OR DISTRIBUTIONin respiratory system mechanics NOTSupport FOR is taken SALE away if ORthe patient’s DISTRIBUTION tidal volume Variable flow may improve synchrony in some consistently exceeds target patients

Adaptive support ventilation (ASV) Ventilator adapts settings to patient’s May not precisely control tidal volume physiology © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Airway pressure release ventilation Allows spontaneous breathing at any time May be uncomfortable for some patients NOT FOR SALE(APRV) OR DISTRIBUTION during the ventilator cycleNOT FOR SALEMay OR result DISTRIBUTION in large tidal volumes, depending on

May improve ventilation to dependent lung Phigh–Plow difference zones May be large transpulmonary pressure swings May improve oxygenation in patients with ALI during spontaneous breathing or ARDS © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Tube compensation (TC) Overcomes resistance through artificial airway Effect is usually small and may not affect patient NOT FOR SALE OR DISTRIBUTION outcomes NOT FOR SALE OR DISTRIBUTION

Proportional assist ventilation (PAV) Pressure applied to the airway is determined Not useful with weak drive or weak respiratory by respiratory drive and respiratory muscles mechanics Clinician has little control over tidal volume or respiratory rate © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NeurallyNOT adjusted FOR ventilatorySALE assistOR DISTRIBUTIONPressure applied to the airway is determined NOTRequires FOR insertion SALE of special OR gastric DISTRIBUTION tube to (NAVA) by diaphragm activity measure diaphragm EMG Not useful with weak respiratory drive or motor neuron disease

PEEP, positive end-expiratory pressure; Phigh, high airway pressure setting; Plow, pressure release level; ALI, acute lung injury; ARDS, acute © Jones & respiratoryBartlett distress Learning, syndrome; EMG,LLC electromyelogram. © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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40 © Jones & Bartlett Learning,30 LLC © Jones & Bartlett Learning, LLC

) 20 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION10 0 L/min ( –10 –20

Flow –30 –40 –50 © Jones &2 Bartlett 4 Learning,6 LLC8 10 12 © Jones14 & Bartlett Learning, LLC

O) NOT24 FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 2 20 16 cm H ( 12 8 4 © Jones & Bartlett0 Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE Pressure OR DISTRIBUTION2 4 6 8 NOT10 FOR12 SALE OR14 DISTRIBUTION 600

) 500 mL

( 400 300 200 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC

Volume Volume 100 NOT FOR SALE OR DISTRIBUTION0 NOT FOR SALE OR DISTRIBUTION 2 4 6 8 10 12 14 Time (s) FIGURE 22–8 Continuous positive airway pressure.

NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ) 40 20 L/min

( 0 –20

Flow –40 © Jones & Bartlett–60 Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION2 4 6 8 NOT10 FOR 12SALE OR14 DISTRIBUTION

O) 24 2 20 16 cm H ( 12 © Jones & Bartlett Learning,8 LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION4 Trigger NOT FOR SALE OR DISTRIBUTION 0 Pressure Pressure 2 4 6 8 10 12 14

600

) 500 mL

( 400© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 300 200NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Volume Volume 100 0 2 4 6 8 10 12 14 Time (s) © Jones &FIGURE Bartlett 22–9 Learning, Pressure support LLC ventilation. © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

be adjusted to a level appropriate for the patient exceeds the termination flow at which the ventilator (Figure 22–11). cycles, either active exhalation occurs to terminate inspi- © Jones & BartlettAnother Learning, concern with LLC PSV is leaks in the system,© Jonesration, & or Bartlett a prolonged Learning, inspiratory LLCtime is applied. With a NOT FOR SALEsuch as ORwith DISTRIBUTIONa bronchopleural fistula, uncuffed airway,NOT leak, FOR either SALE PCV OR or a ventilatorDISTRIBUTION that allows an adjustable or mask leak with noninvasive ventilation. If the leak termination flow should be used. Another option is to

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set a maximum inspiratory time during PSV such that © Jones & Bartlett Learning, LLC © Jonesthe breath & Bartlett can be time Learning, cycled at aLLC clinician-determined C NOT FOR SALEO) OR DISTRIBUTION 1 NOT FOR SALE OR DISTRIBUTION 2 20 setting. This secondary cycle typically has been fixed at a prolonged time to prevent untoward effects of long 1 D inspiratory times. Some new ventilators allow both the B 2 15 flow cycle and time cycle to be set. 2 © Jones & Bartlett Learning, LLCThe flow at the onset of the© inspiratory Jones & phase Bartlett may also Learning, LLC be important during PCV or PSV. This is called rise time NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 10 and refers to the time required for the ventilator to reach the set pressure at the onset of inspiration. Flows that are A too high or too low at the onset of inspiration can cause 5 asynchrony. Most ventilators allow adjustment of the rise Figure 22–12 © (cm H Airway Pressure Proximal Jones & Bartlett Learning, LLC time during© PSV Jones ( & Bartlett). The Learning,rise time should LLC be adjusted to the patient’s comfort, and ventilator graph- NOT FOR SALE OR DISTRIBUTION ics may be NOTuseful FORas a guide SALE to thisOR setting.DISTRIBUTION However, Time a high inspiratory flow at the onset of inspiration may FIGURE 22–10 Design characteristics of a pressure-supported not be beneficial.45 If the flow is higher at the onset of breath. In this example, baseline pressure (i.e., PEEP) is set at 5 cm inspiration, the inspiratory phase may be prematurely H O and pressure support is set at 15 cm H O (PIP 20 cm H O). 2 2 2 terminated during PSV if the ventilator cycles to the © Jones & TheBartlett inspiratory Learning,pressure is triggered LLC at point A by a patient effort © Jones & Bartlett Learning, LLC expiratory phase at a flow that is a fraction of the peak NOT FOR SALEresulting in OR an airway DISTRIBUTION pressure decrease. Demand valve sensitivity and NOT FOR SALE OR DISTRIBUTION responsiveness are characterized by the depth and duration of this inspiratory flow. negative pressure. The rise to pressure (line B) is provided by a fixed Sleep fragmentation may be more likely during PSV high initial flow delivery into the airway. Note that if flows exceed patient than during CMV because there is no backup rate.46 Cen- demand, initial pressure exceeds set level (B1), whereas if flows are less tral apnea during PSV results in an alarm, which awakens than patient demand, a very slow (concave) rise to pressure can occur the patient. The pattern of awakening and breathing (B2). The plateau of pressure© supportJones (line &C) isBartlett maintained byLearning, servo LLC © Jones & Bartlett Learning, LLC control of flow. A smooth plateau reflects appropriate responsiveness with sleeping and apnea results in periodic breathing to patient demand; fluctuationsNOT would FOR reflect SALE less responsiveness OR DISTRIBUTION of the and sleep disruption. This complicationNOT FOR of SALE PSV can OR be DISTRIBUTION servo mechanisms. Termination of pressure support occurs at point D addressed by switching to CMV or by using a lower and should coincide with the end of the spontaneous inspiratory effort. level of pressure support. With CMV, there is a mini- If termination is delayed, the patient actively exhales (bump in pressure above plateau) (D1); if termination is premature, the patient will have mum respiratory rate set. With a lower level of pressure support, Paco will likely be greater, and the associated continued© Jones inspiratory & efforts Bartlett (D2). Modified Learning, from MacIntyre LLC N, et al. The © Jones2 & Bartlett Learning, LLC Nagoya conference on system design and patient-ventilator interactions respiratory drive will decrease the risk of apnea. duringNOT pressure FOR support SALE ventilation. OR Chest DISTRIBUTION. 1990;97:1463–1466. NOT FOR SALE OR DISTRIBUTION

10% 25% 50% 100 100 100 © Jones & Bartlett80 Learning, LLC 80 © Jones & Bartlett 80Learning, LLC

60 60 60 ) NOT FOR SALE40 OR DISTRIBUTION 40 NOT FOR SALE OR40 DISTRIBUTION 20 20 20 L/min ( 0 0 0 –20 –20 –20

Flow –40 –40 –40 –60 © Jones & Bartlett–60 Learning, LLC –60 © Jones & Bartlett Learning, LLC –80 –80 –80 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

20 20 20

2 15 15 15 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC cm H

( 10 10 10 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 5 5 5 Pressure Pressure 0 0 0 1 2 1 2 1 2 © Jones & Bartlett Learning, LLC © JonesTime (s) & Bartlett Learning, LLC NOT FOR SALEFIGURE 22–11OR DISTRIBUTION Effect of changing the flow termination criteria (cycleNOT off flow FOR as a percentageSALE OR of peak DISTRIBUTION flow) during pressure support ventilation. Note the effect on inspiratory time.

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Fast Moderate Slow © Jones & Bartlett100 Learning, LLC 100 © Jones & Bartlett100 Learning, LLC NOT FOR SALE80 OR DISTRIBUTION 80 NOT FOR SALE OR80 DISTRIBUTION

60 60 60 ) 40 40 40 20 20 20 L/min ( 0 0 0 –20 –20 –20 Flow –40 © Jones & Bartlett–40 Learning, LLC –40 © Jones & Bartlett Learning, LLC –60 –60 –60 –80 NOT FOR SALE–80 OR DISTRIBUTION –80 NOT FOR SALE OR DISTRIBUTION

20 20 20

O) 2 ©15 Jones & Bartlett Learning, 15LLC © Jones15 & Bartlett Learning, LLC

cm H NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

( 10 10 10

5 5 5 Pressure Pressure 0 0 0 © Jones & Bartlett Learning,1 LLC2 © 1Jones & Bartlett2 Learning, LLC1 2 NOT FOR SALE OR DISTRIBUTION NOTTime FOR (s) SALE OR DISTRIBUTION FIGURE 22–12 Effect of changing rise time during pressure support ventilation. Note the effect on peak flow.

) 40 NOT FOR SALE OR DISTRIBUTION breathsNOT may FOR be pressureSALE ORsup- DISTRIBUTION 20 ported (Figure 22–14). The L/min ( 0 intent is to provide respiratory –20 muscle rest during mandatory Flow –40 breaths and respiratory mus- ©–60 Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 2 4 6 8 10 12 14 cle exercise with the inter-

NOT FOR SALE OR DISTRIBUTION NOT FOR SALEvening ORbreaths. DISTRIBUTION However, it

O) 24 2 has been shown that con- 20 16 Spontaneous Mandatory siderable inspiratory effort cm H ( 12 breath breath occurs with both the manda- 8 tory breaths and the interven- © Jones & Bartlett4 Learning, LLC © Jones & Bartlett Learning,ing spontaneous LLC breaths. As 0 NOT FOR SALE Pressure OR DISTRIBUTION2 4 6 8 NOT10 FOR 12SALE OR14 DISTRIBUTIONthe level of SIMV support is reduced, the work of breath- 600

ing increases for both manda- ) 500

mL tory and spontaneous breaths

( 400 300 (Figure 22–15).47 This effect 200 © Jones & Bartlett Learning, LLC can© be Jones ameliorated & Bartlett with the Learning, LLC

Volume Volume 100 NOT FOR SALE OR DISTRIBUTION additionNOT ofFOR pressure SALE support, OR DISTRIBUTION 0 2 4 6 8 10 12 14 which results in unloading of Time (s) both mandatory and spontaneous breaths.48 FIGURE 22–13 Synchronized intermittent mandatory ventilation illustrating spontaneous and mandatory breaths. On newer ventilators, a © Jones & Bartlett Learning, LLC © Jones & volumeBartlett feedback Learning, mechanism LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALEfor pressure-controlled OR DISTRIBUTION or pressure-supported breaths Synchronized intermittent mandatory ventilation exists.49,50 This is called adaptive pressure control. The (SIMV) (Figure 22–13) provides mandatory breaths desired tidal volume is set on the ventilator, but the (VCV or PCV) that are interspersed with spontaneous breath type is actually pressure control or pressure © Jones & breaths.Bartlett The Learning, mandatory LLC breaths are delivered at the© Jonessupport. & BartlettThe ventilator Learning, then adjusts LLC the inspiratory NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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60 guaranteed (General Electric).

© Jones & Bartlett) 40 Learning, LLC © Jones & Bartlett Learning,Volume LLC support is a volume NOT FOR SALE20 OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONfeedback mode in which the L/min ( 0 breath type is only pressure –20 support.50 Flow –40 Because breath delivery –60 during these volume feedback 2 © Jones4 & Bartlett6 Learning,8 10 LLC 12 14 © Jones & Bartlett Learning, LLC modes is pressure controlled,

O) 24 2 NOT FOR SALE OR DISTRIBUTION tidalNOT volume FOR will SALE vary ORwith DISTRIBUTION 20 16 Pressure-support Mandatory changes in respiratory system cm H ( 12 breath breath compliance, airway resistance, 8 and patient effort. If changes 4 in lung mechanics cause the 0

Pressure Pressure © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 2 4 6 8 10 12 14 tidal volume to change, the NOT FOR SALE OR DISTRIBUTION NOT FOR SALEventilator OR adjusts DISTRIBUTION the pres- 800

sure setting in an attempt ) 600

mL to restore the tidal volume. ( 400 However, it is important to realize that providing a vol- © Jones & Bartlett200 Learning, LLC © Jones & Bartlett Learning, LLC Volume Volume ume guarantee negates the NOT FOR SALE0 OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 2 4 6 8 10 12 14 pressure-limiting feature of a Time (s) clinician-set pressure control FIGURE 22–14 Synchronized intermittent mandatory ventilation with pressure support of level (i.e., worsening respira- spontaneous breaths. tory system mechanics will © Jones & Bartlett Learning, LLC increase© Jones the applied & Bartlett pressure). Learning, LLC Another potential problem Spontaneous MandatoryNOT FOR SALESpontaneous OR DISTRIBUTIONwith these approaches is thatNOT if the FOR patient’s SALE demand OR DISTRIBUTION breath breath breaths increases and produces a larger tidal volume, the pressure level will diminish, a change that may not be appropriate for a patient in respiratory failure. Flow © Jones & Bartlett Learning, LLC Airway ©pressure Jones release & Bartlett ventilation Learning, (APRV) LLC is a time-cycled, pressure-controlled mode of ventilatory NOT FOR SALE OR DISTRIBUTION support.51 ItNOT is a modificationFOR SALE of OR SIMV DISTRIBUTION with an active Volume exhalation valve that allows the patient to breathe spontaneously throughout the ventilator-imposed pressures (with or without PSV). Because APRV is often used Airway Pressure with a long inspiratory-to-expiratory timing pattern, © Jones & Bartlett Learning, LLC © Jonesmost of& theBartlett spontaneous Learning, breaths LLCwill occur during the NOT FOR SALE OR DISTRIBUTION NOTlong FOR lung SALE inflation OR periodDISTRIBUTION (Figure 22–17). APRV is available under a variety of proprietary trade names: Pressure

Esophageal APRV (Dräger), BiLevel (Puritan Bennett), BiVent (Sie- Time mens), BiPhasic (Avea), PCVϩ (Dräger), and DuoPAP (Hamilton).50 FIGURE 22–15 Synchronized© Jones intermittent & Bartlett mandatory Learning, LLC © Jones & Bartlett Learning, LLC ventilation. Note that the esophageal (i.e., pleural) pressure APRV uses different terminology to describe breath change for the mandatoryNOT breath FOR is nearly SALE as great OR as thatDISTRIBUTION delivery phases. Lung inflationNOT depends FOR SALE on the ORhigh DISTRIBUTION for the spontaneous breaths. airway pressure setting (Phigh). The duration of this

inflation is termed Thigh. Oxygenation is thus heavily

pressure to deliver the set minimal target tidal volume influenced by Phigh, Thigh, and Fio2. The magnitude and Figure 22–16 duration of lung deflation is determined by the pres- ( © Jones ).& IfBartlett tidal volume Learning, increases, LLC the machine © Jones & Bartlett Learning, LLC decreases the inspiratory pressure, and if tidal volume sure release level (Plow) and the release time (Tlow). The decreases,NOT FOR the machine SALE increasesOR DISTRIBUTION the inspiratory pres- ventilator-determinedNOT FOR tidal SALE volume OR is DISTRIBUTION thus dependent sure. This mode goes by the following names: pressure on lung compliance, airways resistance, and the dura- regulated volume control (Maquet Servo-i), AutoFlow tion and timing of this pressure release maneuver. The (Dräger), adaptive pressure ventilation (Hamilton Gali- timing and magnitude of this tidal volume coupled with the patient’s spontaneous breathing determine © Jones & leo),Bartlett volume Learning, control plus LLC(Puritan Bennett), and volume© Jones & Bartlett Learning, LLC targeted pressure control or pressure controlled volume alveolar ventilation (Paco ). As noted earlier, T is NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION2 high

60038_CH22_462_500.pdf 475 11/1/10 11:05 AM 476 CHAPTER 22 Mechanical Ventilation O) O) © Jones & Bartlett2 40 Learning, LLC © Jones2 &40 Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

0 0 40 seconds 40 seconds Pressure (cm H Pressure Pressure (cm H Pressure 80 © Jones & Bartlett Learning, LLC 80 © Jones & Bartlett Learning, LLC

0 NOT FOR SALE OR DISTRIBUTION 0 NOT FOR SALE OR DISTRIBUTION Flow (L/min) –80 Flow (L/min) –80 40 seconds 40 seconds 1000 1000 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Volume (mL) Volume 0 (mL) Volume 0 40 seconds 40 seconds (A) (B) © Jones & BartlettFIGURE 22–16 Learning, (A) Effect ofLLC adaptive pressure control with a compliance© Jones increase & Bartlett or respiratory Learning, effort increase. LLC (B) Effect of adaptive NOT FOR SALEpressure OR control DISTRIBUTION with a compliance decrease or respiratory effortNOT decrease. FOR From SALEBranson RD, OR Johannigman DISTRIBUTION JA. The role of ventilator graphics when setting dual-control modes. Respir Care. 2005;50:187–201. Reprinted with permission.

Paw exchange, often with lower maximal set airway pressures 51 © Jones & Bartlett Learning, LLCthan CMV, has been demonstrated© Jones with & APRV. Bartlett How- Learning, LLC ever, the end-inspiratory alveolar distention in APRV is Phigh NOT FOR SALE OR DISTRIBUTIONnot necessarily less than that providedNOT FOR during SALE other formsOR DISTRIBUTION of support, and it could be substantially higher, because spontaneous tidal volumes can occur while the lung is fully inflated with the APRV set pressure. Randomized con- © Jones & Bartlett Learning, LLC trolled trials© comparing Jones &APRV Bartlett with other Learning, lung-protective LLC strategies have shown no difference in outcome.52,53 Plow NOT FOR SALE OR DISTRIBUTION AdaptiveNOT support FOR ventilation SALE OR (ASV) DISTRIBUTION automatically selects tidal volume and frequency for mandatory breaths Time and the tidal volume for spontaneous breaths on the basis of the respiratory system mechanics and target minute Thigh Tlow ventilation. ASV delivers pressure-controlled breaths © Jones & FIGUREBartlett 22–17 Learning, Airway pressure LLC release ventilation. © Jonesusing an& adaptiveBartlett scheme, Learning, in which LLC the mechanical work NOT FOR SALE OR DISTRIBUTION NOTof FOR breathing SALE is minimized. OR DISTRIBUTION The ventilator selects a tidal volume and frequency that the patient’s brain stem would

usually much greater than Tlow; thus, in the absence of theoretically select. The ventilator calculates the required spontaneous breathing, APRV is functionally the same minute ventilation based on the patient’s ideal body as pressure-controlled inverse ratio ventilation. To sus- weight and estimated dead space volume (2.2 mL/kg). tain optimal recruitment© Jones with APRV, & Bartlett the greater Learning, part of LLCThe clinician sets a target percentage© Jones of& minuteBartlett ven- Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION the total time cycle (80% to 95%) usually occurs at Phigh, tilation that the ventilator will support; for example, whereas in order to minimize derecruitment, the time higher than 100% if the patient has increased ventilatory

spent at Plow is brief (0.2–0.8 second in adults). If Tlow is requirements (e.g., because of sepsis or increased dead too short, exhalation may be incomplete and intrinsic space), or less than 100% during ventilator liberation. PEEP may result. The ventilator measures the expiratory time constant ©Spontaneous Jones & breathing Bartlett during Learning, APRV results LLC from dia- and uses this© Jonesalong with & Bartlettthe estimated Learning, dead space LLC to phragmNOT contraction, FOR SALE which OR should DISTRIBUTION result in recruitment determine NOTan optimal FOR breathing SALE ORfrequency DISTRIBUTION in terms of of dependent alveoli, thus reducing shunt and improving the work of breathing. The target tidal volume is calcu- oxygenation. The spontaneous efforts also may enhance lated as the minute ventilation divided by the frequency, both recruitment and cardiac filling as compared with other and the pressure limit is adjusted to achieve an average controlled forms of support. The long inflation phase also delivered tidal volume equal to the target. The ventila- © Jones & recruitsBartlett more Learning, slowly, filling LLC alveoli and raises mean airway© Jonestor also & adjustsBartlett the Learning,inspiration-to-expiration LLC (I:E) ratio NOT FOR SALEpressure OR without DISTRIBUTION increasing applied PEEP. Improved gasNOT to FOR avoid SALE air trapping. OR DISTRIBUTION ASV has been shown to supply

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reasonable ventilatory support in a O) © Jones &variety Bartlett of patients Learning, with respiratoryLLC 2 15 © Jones & Bartlett Learning, LLC NOT FOR SALEfailure.54–58 OR However, DISTRIBUTION outcome stud- NOT FOR SALE OR DISTRIBUTION cm H ies in patients with acute respiratory ( failure comparing ASV with conventional lung-protective strategies have

Pressure Pressure 0 not been reported. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Tube compensation (TC) is designed to overcomeNOT theFOR flow- SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION resistive work of breathing imposed

by an endotracheal tube or trache- ) 75 ostomy tube.58–61 It measures the L/min ( 0 resistance© Jones of the& Bartlett artificial Learning,airway LLC © Jones & Bartlett Learning, LLC and applies a pressure proportional NOT FOR SALE OR DISTRIBUTIONFlow NOT FOR SALE OR DISTRIBUTION to that resistance. The clinician can –75 set the fraction of tube resistance for which compensation is desired (e.g., 50% compensation rather than © Jones & fullBartlett compensation). Learning, Although LLC it has © Jones & Bartlett Learning, LLC been shown that TC can effectively 0.50

NOT FOR SALE OR DISTRIBUTION ) NOT FOR SALE OR DISTRIBUTION compensate for resistance through L ( the artificial airway, it has not been shown to improve outcome.61 0.25

Proportional assist ventilation Volume 0 (PAV) is a positive-feedback© Jones con-& Bartlett Learning, LLC © Jones & Bartlett Learning, LLC trol mode that provides ventilatory support in proportionNOT to theFOR neural SALE OR DISTRIBUTION5 seconds NOT FOR SALE OR DISTRIBUTION output of the respiratory center.50 FIGURE 22–18 Proportional assist ventilation. From Marantz S, Patrick W, Webster K, et al. The ventilator monitors respiratory Response of ventilator-dependent patients to different levels of proportional assist. J Appl Physiol. drive as the inspiratory flow of the 1996;80:397–403. Reprinted with permission. patient,© Jones integrates & Bartlett flow to volume,Learning, LLC © Jones & Bartlett Learning, LLC measures elastance and resistance, and then calculates PAV/NAVA theNOT pressure FOR required SALE from OR DISTRIBUTIONthe equation of motion. NOT FOR SALE OR DISTRIBUTION Using this calculated pressure and the tidal volume, the ventilator calculates work of breathing (WoB): WoB ϭ ∫P ϫ V. These calculations occur every 5 ms during breath delivery, and thus the applied pressure APC/ASV © Jones & andBartlett inspiratory Learning, time vary LLC breath by breath and within© Jones & Bartlett Learning, LLC PSV/PCV NOT FOR SALEthe breath OR ( FigureDISTRIBUTION 22–18). The ventilator estimatesNOT FORSupport SALE OR DISTRIBUTION resistance and elastance (or compliance) by applying end-inspiratory and end-expiratory pause maneuvers of 300 ms every 4 to 10 seconds. The clinician adjusts the percentage of support (from 5% to 95%), which allows © Jones & Bartlett Learning, LLC © Jones & BartlettVolume Learning, LLC the work to be partitioned between the ventilator and the Effort/drive control patient. Typically, theNOT percentage FOR of SALE support OR is set DISTRIBUTION so that NOT FOR SALE OR DISTRIBUTION FIGURE 22–19 Effect of patient effort on the amount of support the work of breathing is in the range of 0.5 to 1.0 joules provided with various ventilator modes. per liter. If the percentage of support is high, patient work of breathing may be inappropriately low and excessive volume and pressure may be applied (runaway phenom- (Figure 22–19).62 The cycle criterion for PAV is flow and enon).© Jones If the percentage & Bartlett of Learning,support is too LLC low, patient is adjustable© by Jones the clinician, & Bartlett similar toLearning, pressure support LLC workNOT of breathing FOR SALE may be OR excessive. DISTRIBUTION ventilation.NOT PAV requires FOR SALE the presence OR DISTRIBUTION of an intact ven- PAV applies a pressure that will vary from breath to tilatory drive and a functional neuromuscular system. breath depending upon changes in the patient’s elas- PAV is only available on one ventilator in the United tance, resistance, and flow demand. This differs from States (PAVϩ, Puritan Bennett 840) and cannot be PSV or PCV, in which the level of applied pressure is used with noninvasive ventilation because leaks prevent © Jones & constantBartlett regardless Learning, of demand, LLC and from VCV, in which© Jonesaccurate & Bartlettdetermination Learning, of respiratory LLC mechanics. PAV NOT FOR SALEthe level OR of pressure DISTRIBUTION decreases when demand increasesNOT may FOR be moreSALE comfortable OR DISTRIBUTION compared with other modes,63

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and it may be associated with better patient–ventilator Breath Triggering © Jones &synchrony Bartlett andLearning, sleep.64 Whether LLC PAV improves clinical© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOTPositive FOR SALE pressure OR breaths DISTRIBUTION can be either time triggered outcomes remains to be determined. (breaths delivered according to a clinician-set rate or Neurally adjusted ventilatory assist (NAVA) is trig- timer) or patient triggered (breaths triggered by either a gered, limited, and cycled by the electrical activity of the change in circuit pressure or flow resulting from patient diaphragm (diaphragmatic EMG). The neural drive is effort). The patient effort required to trigger the venti- transformed into ventilatory© Jones output & Bartlett (neuro-ventilatory Learning, LLClator is an imposed load for ©the Jones patient. & Pressure Bartlett trig- Learning, LLC coupling). The diaphragmatic EMG is measured by a NOT FOR SALE OR DISTRIBUTIONgering occurs because of a pressureNOT FOR drop SALEin the system OR DISTRIBUTION multiple-array esophageal electrode, which is ampli- (Figure 22–20). The pressure level at which the ventila- fied to determine the support level (NAVA gain). The tor is triggered is set so that the trigger effort is minimal cycle-off is commonly set at 80% of peak inspiratory but auto-triggering is unlikely (typically this is 1 to 2 cm activity. The level of assistance is adjusted in response to H2O below the PEEP or CPAP). Flow triggering is an changes© Jones in neural & Bartlett drive, respiratory Learning, system LLC mechanics, alternative ©to pressureJones &triggering. Bartlett With Learning, flow triggering LLC inspiratory muscle function, and behavioral influences. NOT FOR SALE OR DISTRIBUTION the ventilatorNOT responds FOR to SALE a change OR in DISTRIBUTIONflow rather than Because the trigger is based on diaphragmatic activity a drop in pressure at the airway. With some ventilators, rather than pressure or flow, triggering is not adversely a pneumotachometer is placed between the ventilator affected in patients with flow limitation and auto-PEEP. circuit and the patient to measure inspiratory flow. In NAVA is only available on the Servo-i ventilator. Small other ventilators, a background or base flow and flow © Jones & clinicalBartlett studies Learning, have demonstrated LLC improved trigger and© Jonessensitivity & Bartlett are set. When Learning, the flow LLC in the expiratory cir- cycle synchrony with NAVA,65 but data demonstrating NOT FOR SALE OR DISTRIBUTION NOTcuit FOR decreases SALE by OR the DISTRIBUTIONamount of the flow sensitivity, the improved outcomes are lacking. Another concern with ventilator is triggered. For example, if the base flow is set NAVA is the expense associated with the esophageal at 10 L/min and catheter and the invasive nature of its placement. the flow sensitiv- RESPIRATORY RECAP High-frequency oscillatory ventilation (HFOV) uses ity is set at 3 L/ very high breathing frequencies66 (up to 900 breaths/min Types of Ventilator Triggering © Jones & Bartlett Learning, LLCmin, the ventila- Ventilator© Jones self-triggers & Bartlett when Learning, LLC in the adult) coupled with very small tidal volumes » NOT FOR SALE OR DISTRIBUTIONtor triggers when aNOT set time FOR is reached. SALE OR DISTRIBUTION to provide gas exchange in the lungs. HFOV literally the flow in the » Patient triggers the ventilator vibrates a bias flow of gas delivered at the proximal end of expiratory circuit through changes in pressure the endotracheal tube and effects gas transport through drops to 7 L/min or flow. complex nonconvective gas transport mechanisms. At (the assumption the© alveolar Jones level, & Bartlett the substantial Learning, mean pressure LLC func- is that the ©patient Jones has &inhaled Bartlett at 3 L/min). Learning, Flow LLCtrig- tions as high-level CPAP. The potential advantages to NOT FOR SALE OR DISTRIBUTION gering has NOTbeen shownFOR toSALE reduce OR the DISTRIBUTION work of breath- HFOV are twofold. First, the very small alveolar pressure ing with CPAP.67 However, it may not be superior to swings minimize overdistension and derecruitment. Sec- pressure triggering with pressure-supported breaths or ond, the high mean airway pressure maintains alveolar mandatory breaths.68 Neither pressure triggering nor patency and prevents derecruitment. Experience with flow triggering may be effective if significant auto-PEEP HFOV in neonatal and pediatric respiratory failure is is present. Regardless of whether pressure triggering or © Jones & generallyBartlett positive, Learning, but experience LLC in the adult is limited.© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOTflow FOR triggering SALE isOR used, DISTRIBUTION the current generation of ven- Its use is usually reserved for refractory hypoxemic respi- tilators is more responsive to patient effort, and differ- ratory failure. Whether its use is associated with better ences between pressure and flow triggering are minor.69 patient outcomes is yet to be determined.

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FORBeginning SALE of OR DISTRIBUTION Beginning ofNOT FOR SALE OR DISTRIBUTION patient effort patient effort Pressure Pressure Pressure trigger

© Jones & Bartlett Learning, LLCTime © Jones & Bartlett Learning,Time LLC NOT FOR SALE OR(A)( DISTRIBUTION NOTB FOR) SALE OR DISTRIBUTION FIGURE 22–20 (A) Pressure-triggered breath. (B) Flow-triggered breath.

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Tidal Volume to improve oxygenation, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning,RESPIRATORY LLC RECAP Tidal volume is selected to provide an adequate Paco unless it is coupled with NOT FOR SALE OR DISTRIBUTION NOT2 the FOR ability SALE to spontane- OR DISTRIBUTIONSettings for Tidal Volume, but avoid alveolar overdistention, decreased cardiac Respiratory Rate, and output, and auto-PEEP.70 Tidal volume is directly set ously breathe (see the Inspiratory Time in VCV but is determined by the driving pressure and discussion of APRV ear- » Tidal volume: Set to avoid inspiratory time in PCV and PSV. As noted earlier, large lier in this chapter), this overdistention extreme (and potentially » Respiratory rate: Set for tidal volumes increase© Jonesmortality & in Bartlett patients with Learning, ALI or LLC © Jones & Bartlett Learning, LLC hazardous) form of ven- desired partial pressure ARDS and increase the risk of developing ALI or ARDS of arterial carbon dioxide NOT FOR SALE OR10,71 DISTRIBUTIONtilation is seldom neces- NOT FOR SALE OR DISTRIBUTION in patients with previously normal lungs. A tidal (PaCO ) sary to achieve adequate 2 volume should be chosen that maintains plateau pres- » Inspiratory time: Set to avoid oxygenation. auto-PEEP and hemodynamic sure (Pplat) below 30 cm H2O (assuming a near-normal chest wall compliance), or perhaps higher if chest wall The I:E ratio is the compromise compliance© Jones is &severely Bartlett reduced Learning, (e.g., morbid LLC obesity, relationship© Jonesbetween & Bartlett Learning, LLC inspiratory time and expiratory time. For example, an anasarca,NOT FOR ascites). SALE Tidal OR volume DISTRIBUTION should be selected NOT FOR SALE OR DISTRIBUTION based on predicted body weight (PBW), which is deter- inspiratory time of 2 seconds with an expiratory time of mined by height and sex: 4 seconds produces an I:E ratio of 1:2 and a respiratory rate of 10 breaths/min. With VCV, the peak inspiratory Male patients: PBW ϭ 50 ϩ 2.3 ϫ flow, flow pattern, and tidal volume are the principal [Height (inches) Ϫ 60] © Jones & Bartlett Learning, LLC © Jonesdeterminants & Bartlett of inspiratory Learning, time LLC and the I:E ratio. ϭ ϩ ϫ With PCV, the inspiratory time, I:E ratio, or percent- NOT FOR SALEFemale patients:OR DISTRIBUTION PBW 45.5 2.3 NOT FOR SALE OR DISTRIBUTION [Height (inches) Ϫ 60] age inspiratory time are set directly. In both VCV and PCV, the principal determinant of expiratory time is A reasonable starting point for most patients with respi- the respiratory rate. ratory failure is 6 mL/kg PBW. © Jones & Bartlett Learning, LLCInspiratory Flow Pattern© Jones & Bartlett Learning, LLC Respiratory Rate NOT FOR SALE OR DISTRIBUTIONFor VCV, the inspiratory flowNOT pattern FOR can beSALE constant OR or DISTRIBUTION A respiratory rate is chosen to provide an acceptable descending ramp. For the same inspiratory time, the PIP minute ventilation, as follows: is greater with constant flow than with descending ramp – и flow; the Paw is greater with ramp flow than with con- Ve ϭ Vt ϫ f и stant flow; and gas distribution is better with a descend- where© Jones f is the &respiratory Bartlett rate, Learning, Ve is the LLC minute ven- ing ramp flow© Jonespattern. Because& Bartlett the flow Learning, is greater atLLC the tilation,NOT andFOR Vt SALE is the tidalOR DISTRIBUTIONvolume. A rate of 15 to beginning ofNOT inspiration, FOR SALE patient– OR ventilator DISTRIBUTION synchrony 25 breaths/min is used when mechanical ventilation may be better with a descending ramp flow pattern. is initiated. If a smaller tidal volume is selected to pre- Although the choice of flow pattern often is based on vent alveolar overdistention, a higher respiratory rate clinician bias or the capabilities of a specific ventilator, may be required (25 to 35 breaths/min). The respira- descending ramp flow may be desirable compared with © Jones & toryBartlett rate may Learning, be limited LLC by the development of auto-© Jonesother &inspiratory Bartlett flowLearning, patterns. LLC An end-inspiratory NOT FOR SALEPEEP. The OR minute DISTRIBUTION ventilation that produces a normalNOT pause FOR can SALE be set OR to improve DISTRIBUTION distribution of ventilation, Paco2 without risk for lung injury or auto-PEEP may but this prolongs inspiration and may have a deleterious

not be possible, and the Paco2 thus is allowed to effect on hemodynamics and auto-PEEP. increase (permissive hypercapnia). The inspiratory flow decreases exponentially with PCV and PSV. The peak flow and rate of flow decrease Inspiratory Time© Jones & Bartlett Learning, LLCdepend on the driving pressure,© Jones airways resistance,& Bartlett lung Learning, LLC compliance, and patient effort. With high resistance, For patient-triggeredNOT mandatory FOR breaths, SALE the OR inspiratory DISTRIBUTION NOT FOR SALE OR DISTRIBUTION flow decreases slowly. With a low compliance and long time should be short (1.5 seconds or less) to improve inspiratory time, flow decreases more rapidly, and a ventilator–patient synchrony. A shorter inspiratory time period of zero flow may be present at end-inhalation requires a higher inspiratory flow, which increases the (Figure 22–21). peak inspiratory pressure (PIP) but does not greatly affect© Jones the Pplat. & Increasing Bartlett the Learning, inspiratory timeLLC increases © Jones & Bartlett Learning, LLC – theNOT mean FOR airway SALE pressure OR (P DISTRIBUTIONaw), which may improve Positive End-ExpiratoryNOT FOR SALE Pressure OR DISTRIBUTION oxygenation in some patients with ARDS. When long Because critical care patients are often immobile and inspiratory times are used (over 1.5 seconds) and spon- supine, with compromised cough ability, it is common

taneous breaths are not permitted, paralysis or sedation to use low-level PEEP (3 to 5 cm H2O) with all mechani- (or both) often is required. Long inspiratory times also cally ventilated patients to prevent atelectasis. In patients © Jones & canBartlett cause auto-PEEPLearning, and LLC may result in hemodynamic© Joneswith ALI & Bartlettor ARDS, moreLearning, substantial LLC levels of PEEP may – NOT FOR SALEinstability OR because DISTRIBUTION of the elevated Paw or the auto-PEEP.NOT be FOR required SALE to maintain OR DISTRIBUTION alveolar recruitment. An appro- Although inverse ratio ventilation has been advocated priate PEEP level to maintain alveolar recruitment is

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150 150 Other uses of PEEP include preload and after- © Jones & Bartlett Learning, LLC © Jones &load Bartlett reduction Learning, in the setting LLC of left heart failure, NOT FOR100 SALE OR DISTRIBUTION 100 NOT FORpneumatic SALE OR splinting DISTRIBUTION in the setting of airway mala- 50 50 cia, and facilitation of leak speech with cuff deflation in patients with a tracheostomy.76 0 0 Mean Airway Pressure

Flow (L/min) –50 © Jones Flow (L/min) & Bartlett–50 Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONAcross all modes, oxygenationNOT FOR and cardiacSALE effects OR DISTRIBUTION –100 –100 of mechanical ventilation often correlate best with – – the mean airway pressure (Paw). Indeed, Paw is –150 –150 a key component of the oxygenation index (OI ϭ Time Time ϫ – ϫ 100 [Paw Fio2]/Pao2) that often is used (A) (B) as a more accurate reflection of gas transport © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning,– LLC FIGURE 22–21NOT Flow FOR waveforms SALE during OR pressure DISTRIBUTION control ventilation: low resistance impairment.NOT FOR Factors SALE that affectOR DISTRIBUTION the Paw during and low compliance (A), and high resistance and high compliance (B). mechanical ventilation are the PIP, PEEP, I:E ratio, respiratory rate, and inspiratory flow pattern. Most patients can be managed with mean P values PEEP less than 15 to 20 cm H O. 7 cm H2O 2 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Recruitment Maneuvers NOT FOR SALE OR DISTRIBUTIONSensitivity SensitivityNOT FOR SALE OR DISTRIBUTION –1 cm H2O –1 cm H2O A recruitment maneuver (RM) is an intentional tran- Auto-PEEP Auto-PEEP sient increase in transpulmonary pressure to promote 10 cm H O 3 cm H O 2 2 reopening of unstable collapsed alveoli and thereby improve gas exchange.77 However, although use of © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC PEEP PEEP the maneuver is physiologically reasonable, there 10 cm H2O NOT FOR SALE10 cm OR H2O DISTRIBUTIONhave been no randomizedNOT controlled FOR SALEtrials demon- OR DISTRIBUTION strating an outcome benefit from this improvement in gas exchange. RMs are probably best reserved for Trigger effort = 11 cm H2O Trigger effort = 4 cm H2O the setting of refractory hypoxemia in patients with FIGURE 22–22 Trigger effort is increased when auto-PEEP is present. To trigger ARDS.78 A variety of techniques have been described the ventilator, the patient’s effort must first overcome the level of auto-PEEP that is © Jones & Bartlett Learning, LLC as recruitment© Jones maneuvers & Bartlett (Table 22–3 Learning,). It is uncer- LLC present. Increasing the set PEEP level may raise the trigger level closer to the total PEEP, thus improvingNOT FOR the ability SALE of the patientOR DISTRIBUTIONto trigger the ventilator. However, this tain whetherNOT FOR any one SALE approach OR isDISTRIBUTION superior to the method should not be used if raising the set PEEP level results in an increase in the others. After performing an RM, it is important to total PEEP. set PEEP to a level that retains recruitment. If the lungs are already maximally recruited as the result of PEEP, the benefits of an RM are likely minimal. © Jones RESPIRATORY& Bartlett Learning, RECAP LLCalso part of a lung- protective© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONstrategy. PEEP should beNOT FOR SALE OR DISTRIBUTION Uses of Positive End- used cautiously in patients ■ TABLE 22–3 Different Lung Recruitment Maneuvers Expiratory Pressure with unilateral disease, » Maintain alveolar because it may overdistend Recruitment recruitment Maneuver Method » Counterbalance the more compliant lung, auto-PEEP © Jonescausing & Bartlettshunting of Learning, blood to LLCSustained high- Sustained inflation© Jones delivered & by Bartlettincreasing Learning, LLC pressure inflation PEEP to 30–50 cm H O for 20–40 seconds » Reduce preload and NOT FORthe less SALE compliant OR lung. DISTRIBUTION NOT FOR2 SALE OR DISTRIBUTION afterload PEEP also may be use- Intermittent sigh Periodic sighs with a tidal volume reaching Pneumatic splinting of the » ful to improve triggering by Pplat of 45 cm H O airway 2 patients experiencing auto- » Facilitation of leak speech Extended sigh Stepwise increase in PEEP by 5 cm H O PEEP.72–75 Auto-PEEP func- 2 with a simultaneous stepwise decrease in © Jones & Bartletttions Learning, as a threshold LLC pressure © Jonestidal volume& Bartlett over 2 minutes Learning, leading to aLLC

thatNOT must FOR be overcome SALE ORbefore DISTRIBUTION the pressure (or flow) NOT FORCPAP level SALE of 30 cmOR H2O DISTRIBUTION for 30 seconds decreases at the airway to trigger the ventilator. Increas- ing the set PEEP to a level near the auto-PEEP may Intermittent PEEP Intermittent increase in PEEP from baseline increase to higher level improve the patient’s ability to trigger the ventilator (Figure 22–22). Whenever PEEP is used to overcome the Pressure control Pressure control ventilation of 10–15 cm ϩ © Jones & effectBartlett of auto-PEEP Learning, on triggering, LLC PIP and Pplat must be© Jones PEEP & BartlettH Learning,2O with PEEP of 25–30LLC cm H2O to reach a peak inspiratory pressure of 40–45 cm H O monitored to ensure that increasing the set PEEP does 2 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE ORfor DISTRIBUTION2 minutes not contribute to further hyperinflation.

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Importantly, an RM can produce injury in the form of Volume © Jones &hemodynamic Bartlett Learning, compromise LLC and barotrauma. © Jones & Bartlett Learning,Expired gasLLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Inspired Oxygen Concentration Volume Volume An Fio2 of 1.0 is commonly used when mechanical venti-

lation is initiated. Pulse oximetry (Spo2) is useful to guide Inspired gas titration of the Fio2 (and© Jones PEEP) provided& Bartlett periodic Learning, blood LLC © Jones & Bartlett Learning, LLC gas measurements NOTare obtained FOR SALEto confirm OR the DISTRIBUTION pulse NOT FOR SALEPatient OR DISTRIBUTION oximetry results. RESPIRATORY RECAP A target Spo2 of Setting the Fractional 88% or higher Ventilator Humidifer Inspired Oxygen usually provides FIGURE 22–23 The ability to detect a leak depends on the site Concentration © Jones & Bartlett Learning,a partial LLC pressure where volume ©is measur Jonesed. If &the Bartlett volume on the Learning, inspiratory limb LLC is Initiate mechanical ventilation » of arterial oxygen greater than the volume on the expiratory limb, then there is a leak NOTwith FOR 100% SALEoxygen. OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION in the system (circuit or patient). If the inspired volume at the patient (Pao2) of 60 mm » Titrate the FIO2 to maintain an Hg or higher. is greater than the expired volume at the patient, there is a leak acceptable arterial oxygen in the patient (e.g., around the cuff of the endotracheal tube or a saturation as measured by Although it is bronchopleural fistula). pulse oximetry. common practice © Jones & Bartlett Learning, LLC to wait 20 to 30© Jones & Bartlett Learning, LLC NOT FOR SALEminutes OR after DISTRIBUTION the Fio2 is changed before arterial bloodNOT FOR SALE OR DISTRIBUTION gas measurements are obtained, 10 minutes may be 400 mL is delivered to the patient. For patients ventilated adequate unless the patient has obstructive lung disease, with a small tidal volume, the compressible gas volume which requires a longer equilibration time.79 can greatly affect alveolar ventilation. Some ventilators adjust for the effects of compressible volume such that Sigh © Jones & Bartlett Learning, LLCthe volume chosen by the clinician© Jones is the actual& Bartlett delivered Learning, LLC Vt after correction for the effect of compressible volume. Some ventilators areNOT capable FOR of providing SALE ORperiodic DISTRIBUTION sigh NOT FOR SALE OR DISTRIBUTION The effects of compressible volume on the delivered volumes.80 The rationale for use of sighs is that the Vt, auto-PEEP, plateau pressure, and mixed exhaled periodic hyperinflation reduces the risk of atelectasis. partial pressure of carbon dioxide (Pe–co ) are shown in Indeed, a sigh is actually a very brief RM. For many 2 Equation 22–1. years the use of sighs during mechanical ventilation was The mechanical dead space of the circuit should also not© considered Jones & important. Bartlett However,Learning, several LLC studies of © Jones & Bartlett Learning, LLC be considered. Mechanical dead space is that part of the patientsNOT withFOR ARDS SALE have OR reported DISTRIBUTION improved alveolar NOT FOR SALE OR DISTRIBUTION ventilator circuit through which the patient rebreathes recruitment with the use of sighs.81,82 and thus becomes an extension of the patient’s anatomic dead space. Alveolar ventilation is zero if the sum of the Alarms volume loss in the circuit and the mechanical dead space © Jones & ItBartlett is particularly Learning, important LLC that all alarms be correctly© Jonesis greater & Bartlett than the Vt Learning, set on the ventilator. LLC set on the ventilator. The most important alarm is the NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION patient-disconnect alarm, which can be a low pres- Humidification sure alarm or a low exhaled volume alarm (or both). A Because the function of the upper airway is bypassed sensitive alarm should detect not only disconnection when endotracheal and tracheostomy tubes are used, but also leaks in the system. The ability to detect a leak the inspired gas must be filtered, warmed, and humidi- depends on the site where the volume is measured (Fig- © Jones & Bartlett Learning, LLCfied before delivery to the patient.© Jones All ventilator & Bartlett circuits Learning, LLC ure 22–23). Other alarms set on the ventilator include include a filter in the inspiratory limb and an active or those for high pressure,NOT I:E FORratio, FioSALE, and OR loss DISTRIBUTIONof PEEP. NOT FOR SALE OR DISTRIBUTION 2 passive humidifier. An active humidifier typically humid- To detect changes in resistance and compliance, the peak ifies the inspired gas by passing it over or bubbling it airway pressure alarm is important with VCV, and the through a heated water bath. When an active humidifier low exhaled volume alarm with PCV or PSV. is used, the ventilator circuit may be heated to prevent © Jones & Bartlett Learning, LLC excessive condensation© Jones &in Bartlettthe circuit. Learning, A passive humidi- LLC CircuitNOT FOR SALE OR DISTRIBUTION fier uses anNOT artificial FOR nose SALE (heat and OR moisture DISTRIBUTION exchanger) Because of the gas compression in the ventilator circuit to collect heat and humidity from the patient’s exhaled and the compliance of the ventilator circuit tubing, as gas and returns that to the patient on the next inhala-

much as 3 to 5 mL/cm H2O can be compressed in the tion. Regardless of the humidification technique used, ventilator circuit. In other words, at an airway pres- condensation should be seen in the inspiratory ventila-

© Jones & sureBartlett of 25 cmLearning, H2O above LLC PEEP, about 100 mL of the© Jonestor circuit & Bartlett or the proximal Learning, endotracheal LLC tube or both, NOT FOR SALEgas delivered OR DISTRIBUTION from the ventilator is not delivered to theNOT which FOR indicates SALE ORthat DISTRIBUTIONthe inspired gas is fully saturated patient. If the ventilator is set to deliver 500 mL, only with water vapor.

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© Jones & Bartlett EQUATIONLearning, LLC22–1 © JonesMonitoring & Bartlett the Learning, Mechanically LLC NOT FOR SALE OR DISTRIBUTION NOTVentilated FOR SALE ORPatient DISTRIBUTION Effects of Compressible Volume It is important to monitor the function of the mechanical The effect of compressible volume on ventilator frequently, including checking the ventilator the delivered tidal volume (Vt) can be settings and alarm systems, the humidifier and circuitry, expressed as follows: and the patient’s airway. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 1 VTpt = NOT× VFORTvent SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 1 + (Cpc/Crs) Physical Assessment Asymmetric chest motion may indicate main stem where: (endobronchial) intubation, pneumothorax, or atel- Vtpt ϭ Tidal volume delivered to the ectasis. Paradoxical chest motion may be seen with flail patient© Jones & Bartlett Learning, LLC chest or respiratory© Jones muscle & Bartlett dysfunction. Learning, Retractions LLC CpcNOT ϭ Compliance FOR SALE of the OR ventilator DISTRIBUTION circuit may occur ifNOT the inspiratoryFOR SALE flow OR or sensitivity DISTRIBUTION is inappropriately set or Crs ϭ Compliance of the respiratory if the airway is RESPIRATORY RECAP system obstructed. If Methods of Humidification Vtvent ϭ Tidal volume from the ventilator the patient is not with Mechanical Ventilation © Jones & Bartlettcircuit Learning, LLC © Jonesbreathing & Bartlett in syn- Learning,» Active LLC humidification: Heated humidifier NOT FOR SALE OR DISTRIBUTION NOTchrony FOR SALEwith the OR DISTRIBUTION The effect of compressible volume on ventilator (i.e., is » Passive humidification: Artificial nose auto-PEEP (positive end-expiratory pres- bucking the venti- sure) can be expressed as follows: » The presence of condensate lator), the settings in the inspiratory circuit Crs + Cpc on the ventilator near the patient indicates Auto-PEEP = × Measured Pplat may not be appro- adequate humidification. Cr©s Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONpriate or the pa- NOT FOR SALE OR DISTRIBUTION where auto-PEEP is the patient’s actual tient may need sedation or analgesia or both. A patient auto-PEEP (positive end-expiratory respiratory rate greater than the trigger rate on the pressure). ventilator may indicate the presence of auto-PEEP com- The effect of compressible volume promising triggering. In conjunction with inspection, on© the Jones Pplat (plateau& Bartlett pressure) Learning, can be LLC the chest can© Jones be palpated & Bartlett to assess Learning, the symmetry LLC of expressedNOT FOR as follows: SALE OR DISTRIBUTION chest movement.NOT PalpationFOR SALE of the OR tracheal DISTRIBUTION position can Crs + Cpc help detect pneumothorax. Crepitation indicates sub- Pplat = × Measured auto-PEEP cutaneous emphysema. Percussion can be useful in the Crs detection of unilateral hyperresonance or tympany with where Pplat is the patient’s actual plateau a pneumothorax. Unilateral decreased breath sounds © Jones & Bartlettpressure. Learning, LLC © Jonesmay indicate & Bartlett bronchial Learning, intubation, LLC pneumothorax, atel- The effect of compressible volume on ectasis, or pleural effusion. An end-inspiratory squeak NOT FOR SALEthe mixed OR exhaled DISTRIBUTION partial pressure of car- NOTover FOR the SALE trachea OR usually DISTRIBUTION indicates insufficient air in the – bon dioxide (Peco2) can be expressed as artificial airway cuff. follows: Blood Gas Measurements – ϭ – ϫ VTvent Peco2 Peco2(vent)© Jones & Bartlett Learning, LLCThe earliest indicators of hypoxemia© Jones often & Bartlettare changes Learning, LLC VTpt NOT FOR SALE OR DISTRIBUTIONin the patient’s clinical statusNOT (e.g., restlessnessFOR SALE and ORcon- DISTRIBUTION where: fusion, changes in level of consciousness, tachycardia – ϭ – Peco2 Patient’s actual Peco2 or bradycardia, changes in blood pressure, tachypnea, bucking the ven- Pe–co ϭ Pe–co from the ventilator 2(vent) 2 tilator, cyano- RESPIRATORY RECAP circuit © Jones & Bartlett Learning, LLC sis). The ©most Jones & MonitoringBartlett RequiredLearning, During LLC VtventNOT ϭFOR Tidal SALE volume OR from DISTRIBUTION the ventilator commonlyNOT used FOR SALEMechanical OR Ventilation DISTRIBUTION circuit assessment of » Physical examination oxygenation is the » Blood gas measurements Vtpt ϭ Tidal volume delivered to the partial pressure of » Lung mechanics patient arterial oxygen. » Hemodynamics © Jones & Bartlett Learning, LLC © JonesA low & Pao Bartlett indi- Learning,» Patient–ventilator LLC synchrony 2 » Sedation NOT FOR SALE OR DISTRIBUTION NOTcates FOR hypoxemia SALE OR DISTRIBUTION

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PIP © Jones & Bartlett Learning, LLCPaO2 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONResistance ﬂow

Lung Pplat FIO2 Paw function Compliance tidal volume © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC PEEPNOT FORI:E SALE ratio OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION PEEP Total-PEEP Auto-PEEP

FIGURE 22–24 Factors affecting PaO2 during mechanical ventilation. FIGURE 22–26 Airway pressure waveform during volume © Jones & Bartlett Learning, LLC control ventilation.© Jones An end-inspiratory & Bartlett and anLearning, end-expiratory LLC NOT FOR SALE OR DISTRIBUTION breath holdNOT is applied FOR to measur SALEe plateau OR pressure DISTRIBUTION and auto-PEEP. Note that the difference between peak inspiratory PaCO2 pressure and plateau pressure is determined by the flow setting on the ventilator and airways resistance. Note that the difference between plateau pressure and total PEEP is VCO VA = VE – VD 2 determined by the tidal volume setting on the ventilator and © Jones & Bartlett Learning, LLC © Jonesthe &total Bartlett level of PEEP Learning, (including auto-PEEP). LLC NOT FOR SALE OR DISTRIBUTIONVT f NOT FOR SALE OR DISTRIBUTION has become the standard of care in mechanically venti- Tl TE lated patients. End-tidal Pco2 is used to monitor carbon dioxide levels noninvasively. In patients with normal FIGURE 22–25 Factors affecting PaCO2 during mechanical© Jonesventilation. & Bartlett Learning, LLClungs, end-tidal Pco2 closely© approximates Jones & Bartlett the Paco Learning,2. LLC NOT FOR SALE OR DISTRIBUTIONHowever, in patients with anNOT elevated FOR Vd/Vt, SALE there OR can DISTRIBUTION be a large and inconsistent gradient between the Paco2 and the end-tidal Pco . For this reason, monitoring end- and a dysfunction in the lungs’ ability to oxygenate arte- 2 tidal Pco2 is of limited value for the assessment of the rial blood. The Pao2 must always be interpreted in rela- Paco2 during mechanical ventilation. End-tidal Pco2 is tion to the Fio2 (and often the mean airway pressure). In mechanically© Jones ventilated & Bartlett patients, Learning, a number LLC of factors can useful to differentiate© Jones tracheal & Bartlett intubation Learning, from esopha- LLC geal intubation. affectNOT the FORPao2, suchSALE as aOR change DISTRIBUTION in the Fio2, the PEEP NOT FOR SALE OR DISTRIBUTION level, or the patient’s lung function (Figure 22–24). – – Lung Mechanics The mixed venous oxygenation (Pvo2 or Svo2) is a better indicator of tissue oxygenation. A Pv–o less Monitoring of the peak pressure, Pplat, and auto-PEEP – 2 than 35 mm Hg (or Svo2 less than 70%) indicates tissue is particularly important. Pplat is measured by applica- © Jones & hypoxia.Bartlett The Learning, Paco is determined LLC by carbon dioxide© Jonestion of & an Bartlett end-inspiratory Learning, pause LLCof 0.5 to 1.5 seconds, и 2 и production (Vco ) and the alveolar ventilation (Va). If and auto-PEEP is determined by application of an end- NOT FOR SALEи OR DISTRIBUTION2 NOT FOR SALE OR DISTRIBUTION the Vco is constant, the Paco varies inversely with the expiratory pause of 0.5 to 1.5 seconds (Figure 22–26). и 2 и 2 Va. The minute ventilation (Ve) affects the Paco indi- During PCV the inspiratory flow often decreases to a и2 rectly because of the relationship between the Ve and no-flow period at end-inspiration. In this case, the peak и и the Va. An increase in the Ve decreases the Paco , and a pressure and Pplat are equivalent. Both Pplat and auto- и 2 decrease in the Ve increases© Jones the Paco& Bartlett2. This is illustratedLearning, LLCPEEP can be accurately measured© Jones only when & Bartlett the patient Learning, LLC by the following relationship:NOT FOR SALE OR DISTRIBUTIONis not exerting effort. NOT FOR SALE OR DISTRIBUTION ϭ и ϫ и ϫ Ϫ To avoid overdistention and lung injury, the goal is to Paco2 (Vco2 0.863) / (Ve [1 Vd/Vt]) maintain Pplat below 30 cm H2O (and lower if possible). where Paco is the partial pressure of arterial carbon To assist in this and to minimize unnecessary cardiac и 2 и dioxide, Vco2 is carbon dioxide production, Ve is minute effects and triggering difficulties, auto-PEEP should be ventilation,© Jones and & Vd/Vt Bartlett is the Learning, ratio of dead LLC space to tidal as low as possible,© Jones preferably & Bartlett zero. Learning,Importantly, LLCthese volume.NOT Figure FOR 22–25SALE shows OR theDISTRIBUTION factors that determine circuit measurementsNOT FOR of SALE respiratory OR DISTRIBUTIONsystem pressures

the Paco2 during mechanical ventilation. all assume normal chest wall compliance in order for The use of noninvasive monitors may reduce the them to be a reasonable estimate of transpulmonary need for arterial blood gas determinations, because pressures (i.e., a normal chest wall compliance will they allow continuous assessment between blood gas have little effect on the measured airway pressures). © Jones & measurements.Bartlett Learning, Pulse oximetry LLC can be used to titrate an© JonesIn the & setting Bartlett of abnormal, Learning, very LLC low chest wall com-

NOT FOR SALEappropriate OR FioDISTRIBUTION2 and PEEP. Continuous pulse oximetryNOT pliance FOR SALE(e.g., obesity, OR DISTRIBUTION ascites), these airway pressure

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1.6 1000 © Jones & Bartlett Learning, LLC © Jones & Bartlett900 Learning, LLC

NOT FOR SALE) OR DISTRIBUTION NOT FOR SALE800 OR DISTRIBUTION L ( 1.2 700 C 600 500 0.8 400

© Jones & Bartlett Learning, LLC (mL) Volume © Jones & Bartlett Learning, LLC Upper 300 NOT FOR SALEinﬂection OR pointDISTRIBUTION 200 NOT FOR SALE OR DISTRIBUTION 0.4 Volume Above FR Volume 100 Lower 0 inﬂection point 10 20 30 0.0 Pressure (cm H O) 10 20 30 40 2 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Airway Pressure (cm H2O) NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONPressure FIGURE 22–27 Pressure–volume curve for normal lungs (solid manometer circles) and ARDS (open circles). Note the presence of a lower and upper inflection point on the pressure–volume curve for ARDS.

Calibrated © Jones & measurementsBartlett Learning, may be profoundly LLC affected by chest wall© Jonessyringe & Bartlett Learning, LLC NOT FOR SALEstiffness OR and DISTRIBUTIONthese effects need to be subtracted fromNOT FOR SALE OR DISTRIBUTION Patient the airway pressure to determine true transpulmonary pressure. This can be done directly with an esophageal Filter pressure measurement or estimated by an experienced FIGURE 22–28 Super syringe technique to measure pressure–volume curve. clinician. The use of esophageal pressures for both estimating true transpulmonary© Jones & pressures Bartlett and Learning, assess- LLC © Jones & Bartlett Learning, LLC ing the triggering loadsNOT from FOR auto-PEEP SALE is OR described DISTRIBUTION in NOT FOR SALE OR DISTRIBUTION more detail next. the effects of resistance on the pressure measurement. Auto-PEEP has other manifestations that can be mon- The role of the PV curve in setting the ventilator cur- itored. The patient’s breathing pattern can be observed; rently is unclear. Although its use is physiologically if exhalation is still occurring when the next breath is attractive, more experience is needed with these mea- delivered,© Jones auto-PEEP & Bartlett is present. Learning, Inspiratory LLC efforts that surements before© Jones the PV & curve Bartlett can be Learning, recommended LLC for do NOTnot trigger FOR the SALE ventilator OR suggest DISTRIBUTION the presence of auto- routine use NOTin setting FOR the SALEventilator. OR DISTRIBUTION PEEP. From the flow graphics on the ventilator, it can be The stress index is a method to assess the level of observed that expiratory flow does not return to zero PEEP to avoid overdistension and underrecruitment before the subsequent breath is delivered when auto- (Figure 22–29).84 This approach uses the shape of the PEEP is present. pressure–time curve during constant-flow tidal volume © Jones & BartlettThe inflation Learning, pressure–volume LLC (PV) curve of the© Jonesdelivery. & BartlettIf the compliance Learning, is worsening LLC as the lungs 83 Ͼ NOT FOR SALErespiratory OR system DISTRIBUTION can be used to set the ventilator.NOTare FOR inflated SALE (upward OR DISTRIBUTIONconcavity, stress index 1), this For patients with ARDS, the PV curve is sigmoidal suggests overdistension, and the recommendation is (Figure 22–27). A lower inflection point presumably to decrease PEEP or tidal volume. If the compliance is represents the pressure at which a large number of improving as the lungs are inflated (downward concav- alveoli are recruited, or opened. An upper inflection ity, stress index Ͻ 1), this suggests further potential for point presumably represents© Jones the & Bartlettpressure at Learning, which a LLCrecruitment, and the recommendation© Jones & is Bartlettto increase Learning, LLC large number of alveoliNOT are FOR overdistended. SALE OR Therefore, DISTRIBUTION it PEEP. The ideal stress index isNOT 1, in which FOR there SALE is a linearOR DISTRIBUTION would seem reasonable to set the PEEP above the lower increase in pressure with constant-flow inflation of the inflection point and the Pplat below the upper inflection lungs. point. Because there is hysteresis in the PV curve (i.e., Esophageal pressure is measured from a thin-walled it is shifted leftward during deflation), some argue that balloon, which contains a small volume of air (Ͻ1 mL), the© ideal Jones PEEP & setting Bartlett should Learning, be determined LLC during the placed into© theJones lower & esophagus Bartlett Learning,(Figure 22–30 LLC).85 deflationNOT phaseFOR ofSALE the PV OR plot. DISTRIBUTION EsophagealNOT pressure FOR changes SALE reflect OR changes DISTRIBUTION in pleural The traditional PV curve is measured as a series of pressure, but the absolute esophageal pressure does not plateau pressures during small incremental changes in reflect absolute pleural pressure. Changes in esophageal inspiratory and expiratory volumes from a super syringe pressure can be used to assess respiratory effort and (Figure 22–28). The inflation PV curve can also be mea- patient work of breathing during spontaneous breath- © Jones & suredBartlett when Learning, a slow (e.g., 5LLC to 10 L/min), constant flow is© Jonesing and & patient-triggered Bartlett Learning, modes ofLLC ventilation, to assess NOT FOR SALEset on the OR ventilator DISTRIBUTION and the ventilator display of the PVNOT chest FOR wall SALE compliance OR DISTRIBUTION during full ventilatory support, curve is observed. This slow flow effectively eliminates and to assess auto-PEEP during spontaneous breathing

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Tidal Recruitment Overdistention © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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

Stress index < 1 Stress index = 1 Stress index > 1 © Jones & Bartlett Learning,FIGURE LLC 22–29 Stress index concept during© constant-flow Jones &volume Bartlett control ventilation. Learning, For a LLC NOT FOR SALE OR DISTRIBUTIONstress index less than 1, the airway pressure NOTcurve presents FOR a SALEdownward OR concavity, DISTRIBUTION suggesting a continuous decrease in elastance and tidal recruitment. For a stress index higher than 1, the curve presents an upward concavity, suggesting a continuous increase in elastance and overdistention. For a stress index equal to 1, the curve is straight, suggesting the absence of tidal variations in elastance. Reprinted with permission of the American Thoracic Society. Copyright © American Thoracic Society. Grasso S, Stripoli T, De Michele M, et al. ARDSnet ventilatory protocol and alveolar© Jones hyperinflation: & Bartlett role of positive Learning, end-expiratory LLC pressure. Am J Respir Crit Care Med©. Jones & Bartlett Learning, LLC 2007;176:761–767.NOT FOR SALE Official JournalOR DISTRIBUTION of the American Thoracic Society; Diane Gern, Publisher.NOT FOR SALE OR DISTRIBUTION 1

0 Flow (L/s) © Jones & Bartlett Learning, LLC 0.8 © Jones & Bartlett Learning, LLC NOTCatheter FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Volume (L) Volume 0 30 O) © Jones & Bartlett Learning, LLC © Jones2 & Bartlett Learning, LLC Pressure NOT FOR SALE OR DISTRIBUTION NOT FOR(cm H 0SALE OR DISTRIBUTION 20 Esophageal O) balloon 2

Pes 0 Estimation of Missed © Jones & Bartlett Learning, LLC(cm H auto-PEEP trigger© Jones effort & Bartlett Learning, LLC

FIGURE 22–30 PositionNOT of esophagealFOR SALE balloon ORto measure DISTRIBUTION NOTTime FOR SALE OR DISTRIBUTION changes in intrapleural pressure. FIGURE 22–31 Auto-PEEP. Note the amount of effort required to trigger the ventilator, represented by the amount of decrease in esophageal pressure required for triggering. Also note the presence of an inspiratory effort that does not trigger the ventilator. and© patient-triggered Jones & Bartlett modes Learning, of ventilation. LLC If exhala- © Jones & Bartlett Learning, LLC tion is passive, the change in esophageal (i.e., pleural) NOT FOR SALE OR DISTRIBUTION recognizedNOT as a patientFOR SALErespiratory OR rateDISTRIBUTION (observed by pressure required to reverse flow at the proximal airway inspecting chest wall movement) that is greater than the (i.e., to trigger the ventilator) reflects the amount of trigger rate on the ventilator. auto-PEEP. Negative esophageal pressure changes that The increase in esophageal pressure (⌬Pes) during produce no flow at the airway indicate failed trigger passive inflation of the lungs can be used to calculate efforts; in other words, the patient’s inspiratory efforts © Jones & Bartlett Learning, LLC © Joneschest wall& Bartlett compliance Learning, (Figure 22–32 LLC): NOT FOR SALEare insufficient OR DISTRIBUTION to overcome the level of auto-PEEP andNOT FOR SALE OR DISTRIBUTION trigger the ventilator (Figure 22–31). Clinically, this is Ccw ϭ Vt/⌬Pes

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Changes in esophageal pressure, relative to changes in positive (i.e., PEEP is greater than esophageal pressure) © Jones &alveolar Bartlett pressure, Learning, can be LLC used to calculate transpul-© Jones(Figure & 22–33Bartlett). This Learning, is most likely LLC with a decrease in NOT FOR SALEmonary ORpressure DISTRIBUTION (lung stress). This may allow moreNOT chest FOR wall SALE compliance, OR DISTRIBUTION such as occurs with abdominal precise setting of tidal volume (and Pplat) in patients compartment syndrome, pleural effusion, or obesity. In with reduced chest wall compliance. In this case, trans- this case, it is desirable to keep PEEP greater than pleural pulmonary pressure (difference between Pplat and Pes) pressure. Unfortunately, artifacts in esophageal pressure, is targeted at less than 27 cm H O. especially in supine critically ill patients, make it very diffi- © Jones2 & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC The use of an esophageal balloon has been advocated cult to measure absolute pleural pressure accurately.87,88 In to allow more preciseNOT setting FOR of PEEP. SALE86 If pleural OR DISTRIBUTIONpressure patients with abdominal compartmentNOT FOR syndrome, SALE bladder OR DISTRIBUTION is high relative to alveolar pressure (i.e., PEEP), then there pressure may be useful to assess intra-abdominal pres- may be a potential for derecruitment. With this approach, sure, the potential collapsing effect on the lungs, and the PEEP is increased until the transpulmonary pressure is amount of PEEP necessary to counterbalance this effect.89 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT60 FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 40 20 0 –20

© Jones & BartlettFlow (L/min) –40 Learning, LLC © Jones & Bartlett Learning, LLC –60 NOT FOR SALE OR DISTRIBUTION1 2 NOT FOR SALE3 OR DISTRIBUTION4 5 32 Ccw = VT/⌬Pes O) O) Airway pressure 2 2 24 = 350 mL/5 cm H2O = 70 mL/cm H O 16 Esophageal pressure 2 8 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Pes (cm H Paw (cm H 0 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 1 2 3 4 5 400 300 200 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 100 Volume (mL) Volume NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 0 1 2 3 4 5 Time (s)

FIGURE 22–32 Calculation of chest wall compliance. The esophageal pressure increases by 5 cm H2O with a tidal volume of 350 mL in a passively ventilated patient. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE60 OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 40 20 0

–20 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Flow (L/min) –40 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 2 4 6 8 10 12 14 40 O) O)

2 30 2

©20 Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 10 Pes (cm H Paw (cm H 0 2 4 6 8 10 12 14 © Jones & Bartlett Learning, LLC Time© Jones (s) & Bartlett Learning, LLC FIGURE 22–33 Airway and esophageal pressures in a passively ventilated patient. In this case, the transpulmonary pressure during exhalation is NOT FORpositive SALE because OR PEEP DISTRIBUTION is greater than the esophageal pressure. NOT FOR SALE OR DISTRIBUTION

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are lowest) to account for the respiratory varia- After bronchodilator © Jones & Bartlett Learning, LLC © Jones &tion Bartlett in pleural Learning, pressure. At LLC end-exhalation, mea- NOT FOR SALE60 OR DISTRIBUTION NOT FORsurements SALE OR such DISTRIBUTION as the pulmonary artery wedge Before bronchodilator pressure, pulmonary artery pressure, and central 45 venous pressure are affected by the amount of PEEP transmitted to the pleural space, which is 30 © Jones & Bartlett Learning, LLC determined by lung compliance© Jones &and Bartlett chest wall Learning, LLC Expiration compliance. In patients with normal chest NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 15 wall compliance (over 150 mL/cm H2O) and decreased lung compliance (under 50 mL/cm Volume (mL) 0 H2O), less than one-fourth of the alveolar pressure 200 400 600 900 is transmitted to the pleural space.

Flow (L/min) In addition to esophageal pressure measure- ©–15 Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ments, changes in the pleural pressure can also be NOT FOR SALE OR DISTRIBUTIONInspiration estimatedNOT through FOR SALE observation OR ofDISTRIBUTION the respiratory –30 variation in the thoracic vascular catheter pressure measurements (i.e., the central venous –45 pressure, pulmonary artery pressure, and pul- © Jones & Bartlett Learning, LLC © Jones &monary Bartlett artery Learning, occlusion pressure).LLC With a stiff –60 chest wall, the esophageal pressure or vascular NOT FOR SALEFIGURE OR22–34 DISTRIBUTION Flow–volume loops showing a response to bronchodilatorNOT FORpressure SALE ORshows DISTRIBUTION greater fluctuation during the administration. The expiratory limb of the curve is concave in patients with respiratory cycle, and greater effects of positive expiratory flow limitation. Administration of a bronchodilator aerosol leads to pressure ventilation on hemodynamics can be improvement in expiratory flow. From MacIntyre NM, Branson RD. Mechanical expected. Ventilation. WB Saunders; 2001:17. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONPatient–Ventilator Interactions:NOT FOR SALE OR DISTRIBUTION Synchrony and Asynchrony In patients with obstructive lung disease, it may be use- During any patient-triggered breath, the patient’s effort ful to monitor the flow–volume curve during mechanical must interact with the ventilator’s gas delivery algorithm. ventilation (Figure 22–34). The flow–volume curve may © Jones & Bartlett Learning, LLC These interactions© Jones are & considered Bartlett synchronousLearning, whenLLC provide insight into the severity of airflow obstruction ventilator flow is in phase with patient effort. In contrast, 90 andNOT response FOR to bronchodilatorSALE OR DISTRIBUTION administration. asynchronousNOT interactions FOR SALE occur ORwhen DISTRIBUTION these processes are out of phase. At its worse, asynchrony appears as if Hemodynamics the patient is fighting or bucking the ventilator. How- Because positive pressure ventilation can affect cardiac ever, asynchrony often is much more subtle. Failure of function, it is important to assess hemodynamics during the patient to breathe in synchrony with the ventilator © Jones & mechanicalBartlett Learning,ventilation. At LLC a minimum, the arterial blood© Jonesdecreases & Bartlett patient comfort Learning, and increases LLC both the work of NOT FOR SALEpressure OR and DISTRIBUTIONheart rate should be measured frequently.NOT breathing FOR SALE and the OR oxygen DISTRIBUTION cost of breathing. Asynchrony When the high airway pressures needed to support oxy- often leads to increased sedation needs and has been genation adversely affect cardiac performance, hemody- associated with longer time on mechanical ventilation.91,92 namics may need to be supported with fluid, inotropes, Asynchrony can be categorized as trigger asynchrony, and pressors. The role of the pulmonary artery cath- flow asynchrony, cycle asynchrony, and mode asynchrony. eter in mechanical ventilation© Jones is &unclear, Bartlett and itsLearning, use has LLCTrigger asynchrony occurs© when Jones the patient& Bartlett has dif- Learning, LLC declined in recent years.NOT FOR SALE OR DISTRIBUTIONficulty triggering the ventilatorNOT or FORthe ventilator SALE auto-OR DISTRIBUTION It is important to appreciate the effect of positive pres- triggers. The ventilator trigger sensitivity should be as sure ventilation on hemodynamic assessments. During sensitive as possible without causing auto-triggering. positive pressure ventilation, pleural pressure increases Inability of the patient to trigger can be caused by during inhalation by an amount determined by lung an insensitive trigger setting on the ventilator, which compliance© Jones and & chest Bartlett wall compliance: Learning,89 LLC can be corrected© Jones by reduction & Bartlett of the Learning, pressure or LLC flow NOT FOR SALE OR DISTRIBUTION required forNOT the patient FOR toSALE trigger OR the DISTRIBUTIONventilator. Inabil- ⌬Ppl/⌬Pplat ϭ Cl / (Cl ϩ Ccw) ity to trigger also can be due to respiratory muscle where ⌬Ppl is the change in pleural pressure, ⌬Pplat weakness. Perhaps the most common cause of failure to is the change in alveolar pressure, Cl is lung com- trigger is auto-PEEP in patients with obstructive airway pliance, and Ccw is chest wall compliance. By con- disease. As noted earlier, auto-PEEP can be reduced by © Jones & vention,Bartlett hemodynamic Learning, LLCmeasurements are made at© Joneslowering & Bartlettminute ventilation, Learning, shortening LLC the I:E ratio, or NOT FOR SALEend-exhalation OR DISTRIBUTION (i.e., when transpulmonary pressuresNOT reducing FOR SALE airway ORobstruction DISTRIBUTION through administration of

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bronchodilators and clearing of secretions. Using PEEP by adjusting the trigger sensitivity. Other causes of auto- © Jones &to Bartlett counterbalance Learning, auto-PEEP LLC and thus reduce the trig-© Jonestriggering & Bartlett include excessive Learning, water LLC condensation in the NOT FOR SALEgering loadOR canDISTRIBUTION be effective for patients with COPD,NOT ventilator FOR SALE circuit OR and leaksDISTRIBUTION in the circuit. These causes of but this technique is not effective if the auto-PEEP is auto-triggering are addressed by draining the circuit and primarily the result of a high minute ventilation and correcting the leak. insufficient expiratory time. Whenever PEEP is used Flow asynchrony occurs when the ventilator does to counterbalance auto-PEEP,© Jones &care Bartlett must be Learning, taken to LLCnot meet the patient’s inspiratory© Jones flow &demand. Bartlett Lack Learning, LLC avoid hyperinflation with the PEEP. When the attempt of synchrony can be detected by evaluating the airway is to counterbalanceNOT auto-PEEP FOR with SALE PEEP, OR the clinicianDISTRIBUTION pressure waveform. With NOTasynchrony, FOR SALEthe pressure OR DISTRIBUTION should monitor the peak inspiratory pressure as PEEP is waveform with each breath differs from every other, increased. If the PIP rises above the desired threshold or and there is breath-to-breath variability in the peak increases by a value greater than the increase in PEEP, airway pressure (Figure 22–35). A good way to detect overdistention© Jones &should Bartlett be suspected. Learning, LLC asynchrony© is Jones to compare & Bartlett patient-triggered Learning, breaths LLC Another form of trigger asynchrony is auto-trigger- with a breath delivered via the manual breath control. ing.NOT Auto-triggering FOR SALE causes OR the DISTRIBUTION ventilator to trigger in ComparingNOT the shape FOR of SALE the mandatory OR DISTRIBUTION and sponta- response to an artifact. One artifact that can produce neous breaths on the pressure–time waveform can auto-triggering is cardiac oscillations.93 This is addressed demonstrate the effects of patient effort (i.e., a vigorous

Flow (L/min) –30 –40 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC –50 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 2 4 6 8 10 12 14 24 20 O) O)

2 16 2 12 8 © 4Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 0 Pes (cm H Paw (cm H NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION –4 –8 2 4 6 8 10 12 14 Time (s) (A) © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE60 OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 50 40 30 20 10 0 –10

Flow (L/min) –20 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC –30 –40 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION –50 2 4 6 8 10 12 14 40 O) O) 2 2 ©30 Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT20 FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Pes (cm H Paw (cm H 10

0 2 4 6 8 10 12 14 Time (s) © Jones &(B) Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FORFIGURE SALE 22–35 OR(A) The DISTRIBUTION inspiratory effort of the patient is not met by fixed NOTflow from FOR the ventilator SALE during OR pressure DISTRIBUTION control ventilation. The dashed line represents the airway pressure curve that would result from passive inflation, and the shaded area represents the work done by the patient against the insufficient flow from the ventilator. (B) When the flow setting of the ventilator is increased, the patient is more synchronous with the ventilator.

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patient effort literally sucks the airway pressure graphic is necessary to bring a patient into synchrony with the © Jones &downward). Bartlett Learning, Clinical signs LLC of asynchrony include tachy-© Jonesventilator, & Bartlett propofol Learning, may be useful. LLC When ventilation NOT FOR SALEpnea, retractions, OR DISTRIBUTION and chest-abdominal paradox. FlowNOT requires FOR SALE long inspiratory OR DISTRIBUTION times and high airway pres- asynchrony can be corrected by an increase in the flow sures, pharmacologic control of the patient’s breathing is setting or change in the inspiratory flow pattern during almost always necessary. VCV, by changing from VCV to PCV,35,36,94 or by an 1 increase in the pressure© Jones setting or& theBartlett rise time Learning, set- LLC © Jones & Bartlett Learning, LLC ting during PCV or PSV. However, asynchrony can Flow also occur with PCVNOT (Figure FOR 22–36 SALE).95 For OR patients DISTRIBUTION (L/s) NOT FOR SALE OR DISTRIBUTION who have a high respiratory drive because of anxi- 0.8 ety or pain, flow asynchrony may be improved by 95 (L)

appropriate use of sedation or analgesia. Volume Cycle asynchrony occurs when the neural inspira- 30 © Jones & Bartlett Learning, LLC O) © Jones & Bartlett Learning, LLC tory time of the patient does not match the inspira- 2

toryNOT time settingFOR SALEon the ventilator. OR DISTRIBUTION If the inspiratory Paw NOT FOR SALE OR DISTRIBUTION (cm H time is too short, the patient might double-trigger 40

Figure 22–37 O)

the ventilator ( ). During volume con- 2

trol ventilation, this can cause breath stacking, such Pes

© Jones & thatBartlett the patient Learning, is effectively LLC receiving a tidal volume © Jones(cm H & Bartlett Learning, LLC twice what is set. If the inspiratory time is too long, Time (s) NOT FOR SALEthe patient OR will DISTRIBUTION actively exhale against the ventilator- FIGURENOT FOR 22–36 SALE Patient–ventilator OR DISTRIBUTION asynchrony in a patient receiving pressure delivered breath. Cycle asynchrony can occur during control ventilation. From Kallet RH, Campbell AR, Dicker RA, et al. Work of breathing PSV in patients with obstructive lung disease or during lung-protective ventilation in patients with acute lung injury and acute when a leak is present. Cycle asynchrony during PSV respiratory distress syndrome: a comparison between volume and pressure-regulated breathing modes. Respir Care. 2005;50:1623–1631. Reprinted with permission. can be corrected by© lowering Jones the & pressureBartlett support Learning, LLC © Jones & Bartlett Learning, LLC level, by an increase in the termination flow setting on newer-generationNOT FOR ventilators, SALE ORor DISTRIBUTION NOT FOR SALE OR DISTRIBUTION by use of pressure control instead of pressure

support (pressure control causes inspiration Inhalation to be time cycled rather than flow cycled). Time Flow Cycle© Jonesasynchrony & Bartlett is recognized Learning, as activation LLC © Jones & Bartlett Learning, LLC of the expiratory (abdominal) muscles during

theNOT inspiratory FOR phase;SALE this OR can DISTRIBUTION be detected Exhalation NOT FOR SALE OR DISTRIBUTION clinically by palpation of the patient’s abdo- FIGURE 22–37 Double-triggering. Note that the patient receives two breaths in men. Cycle asynchrony can also be detected rapid succession. Adapted from Pohlman MC, et al. Excessive tidal volume from by observation of the ventilator graphics (Fig- breath stacking during lung-protective ventilation for acute lung injury. Crit Care Med. ure 22–38). 2008;36:3019–3023. © Jones & BartlettMode asynchrony Learning, occurs LLC when the ventila- © Jones & Bartlett Learning, LLC

NOT FOR SALEtor delivers OR different DISTRIBUTION breath types. With SIMV, O) NOT FOR SALE OR DISTRIBUTION 2 30 for example, some breath types are manda- Pressure spike tory and others are spontaneous. Because the patient’s respiratory center cannot adapt to varying breath types, asynchrony can develop © Jones & Bartlett Learning,–10 LLC © Jones & Bartlett Learning, LLC

between the patient and the ventilator. Another (cm H Pressure form of mode asynchronyNOT occursFOR SALEwith adap- OR DISTRIBUTION2 4 6 NOT7 FOR 10SALE OR12 DISTRIBUTION 60 tive pressure control, in which the ventilator Flow = reduces support when the patient’s efforts 35 L/min result in a tidal volume that exceeds the set tidal volume.49,97

© Jones & Bartlett Learning, LLC Flow (L/min) © Jones & Bartlett Learning, LLC –60 NOT FOR SALE OR DISTRIBUTION 2 NOT4 FOR6 SALE 7OR DISTRIBUTION10 12 Sedation Time (s) Anxiety is a common cause of failure to FIGURE 22–38 Airway pressure and flow waveforms illustrating active exhalation during breathe in synchrony with the ventilator. In pressure support ventilation. Note that the flow does not decelerate to the flow termination these cases pharmacologic support may be criterion of the ventilator (5 L/min for this specific ventilator). Also note the presence of © Jones & Bartlett Learning, LLC a pressure© spikeJones at the & end Bartlett of each inspiration, Learning, indicating LLC that the ventilator is pressure necessary in the form of analgesics (narcot- NOT FOR SALE OR DISTRIBUTION cycling ratherNOT than FOR flow cycling. SALE Modified OR fromDISTRIBUTION Branson RD. Modes of ventilator operation. In: ics), sedatives (benzodiazepines), or (rarely) MacIntyre NR, Branson RD, eds. Mechanical Ventilation. Philadelphia: WB Saunders; 2000. paralyzing agents. When short-term sedation Copyright Elsevier 2000.

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It must be remembered that all forms of respiratory severe acidosis, provided that the Pplat does not exceed © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC suppression are associated with adverse side effects. It 30 cm H2O. Respiratory rate is adjusted to control pH. The NOT FOR SALEis most ORimportant DISTRIBUTION that disconnect alarms be properlyNOT potential FOR SALE for air trapping OR DISTRIBUTION in parenchymal lung injury is low set when the patient’s ability to breathe spontane- if the breathing frequency is less than 35 breaths/min. ously is pharmacologically suppressed. Significant An increased inspiratory time, and even inverse ratio ven-

problems with pharmacologic suppression of respira- tilation (e.g., APRV), can be used to increase Pao2 with tion have been reported,© Jones such & as Bartlett long-term Learning, respira- LLCrefractory hypoxemia. The ©mechanisms Jones & for Bartlett improved Learning, LLC tory muscle weakness after use of paralyzing agents oxygenation with inverse ratio ventilation include longer during mechanical NOTventilation. FOR98,99 SALE It has OR been DISTRIBUTION shown gas mixing time, recruitmentNOT of slowly FOR filling SALE alveoli, OR and DISTRIBUTION that assessment of the patient’s response to a daily development of auto-PEEP. trial of sedation cessation significantly reduces the Although imaging or mechanical techniques to days of mechanical ventilation.100 This suggests that guide proper PEEP settings have physiologic appeal, many© Jonesmechanically & Bartlett ventilated Learning, patients are LLC excessively they are technically© Jones challenging & Bartlett and Learning, not practical LLC for sedated and that this excessive sedation prolongs the routine use. Thus, most clinicians rely on various gas NOT FOR SALE OR DISTRIBUTION100,101 NOT FOR SALE OR DISTRIBUTION course of mechanical ventilation. exchange criteria to guide PEEP and Fio2 titrations. This involves the use of algorithms designed to provide

adequate oxygenation (Pao2 55 to 80 mm Hg or Spo2 of

Choosing Ventilator Settings for 88% to 95%) while minimizing Fio2. An example would © Jones & DifferentBartlett Learning, Forms LLCof Respiratory © Jonesbe the & National Bartlett Institutes Learning, of Health’s LLC ARDS Network PEEP/Fio algorithm (Figure 22–39).12,103 Note that NOT FOR SALEFailure OR DISTRIBUTION NOT FOR SALE2 OR DISTRIBUTION this PEEP/Fio2 algorithm attempts to balance pressure

ALI and ARDS (Parenchymal Lung Injury) administration (PEEP) with Spo2 or Pao2 and with Fio2. With ALI and ARDS, lung compliance is low and lung vol- Randomized controlled trials have compared various ume is decreased. It is important to realize, however, that gas exchange strategies for setting PEEP in conjunc- there are often marked© Jonesregional differences& Bartlett in theLearning, degree LLCtion with low Vt strategies and© Joneshave reported & Bartlett that both Learning, LLC aggressive (i.e., 13 to 15 cm H O PEEP) and conserva- of alveolar involvement. Whereas some alveoli may be col- 2 NOT FOR SALE OR DISTRIBUTIONtive (i.e., 7 to 9 cm H O) approachesNOT FOR have SALE comparable OR DISTRIBUTION lapsed or consolidated, others may be hyperinflated and 2 outcomes.103–105 In terms of hospital survival, however, others may be normal. The tidal volume will preferentially a recent meta-analysis of these studies suggests that go to the regions with the more normal mechanics. A higher levels of PEEP may be beneficial for patients with normal tidal volume may thus be distributed preferentially ARDS (Pao /Fio Յ 200 mm Hg), whereas higher levels to the© Joneshealthier & regions Bartlett of the Learning, lungs, resulting LLC in potential ©2 Jones2 & Bartlett Learning, LLC of PEEP are not beneficial (and may produce harm) in for regional overdistention injury. Parenchymal injury can NOT FOR SALE OR DISTRIBUTION patients withNOT ALI FOR(Pao /Fio SALE Ͼ 200 OR mm DISTRIBUTION Hg).105,106 also affect the airways, which can contribute to reduced 2 2 Some mechanical approaches to setting PEEP are regional ventilation to injured lung units. Gas exchange practiced in ICUs where the staff has considerable experi- abnormalities with ALI and ARDS are a consequence и и ence managing ALI and ARDS (Box 22–6). These include of alveolar flooding and/or collapse, resulting in V/Q и и titration to the highest compliance,107 titration to a pres- mismatching and shunts. The low-V/Q regions result in © Jones & Bartlett Learning, LLCи и © Jonessure greater & Bartlett than the Learning, lower inflection LLC point of the pres- hypoxemia, and the high-V/Q regions result in increased NOT FOR SALE OR DISTRIBUTION NOTsure–volume FOR SALE curve, OR83 DISTRIBUTIONand the best stress index.84 PEEP dead space and hypercarbia. should be avoided that results in a Pplat above 30 cm H O. Frequency–tidal volume settings for ALI and ARDS 2 Higher levels of PEEP should be reserved for cases where focus on limiting end-inspiratory alveolar stretch, which has been shown to improve patient outcomes.10–18,102 This has been © Jones & BartlettLower PEEP Learning, Strategy LLC © Jones & Bartlett Learning, LLC most convincingly NOTdemonstrated FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION by the ARDS Network Trial, which FIO2 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7 0.7 0.8 0.9 0.9 0.9 1.0 reported a 10% absolute reduction PEEP 5 5 8 8 10 10 10 12 14 14 14 16 18 18–24 in mortality with a ventilator strategy using a Vt of 6 mL/kg ideal body (A) weight compared with 12 mL/kg.12 © Jones & Bartlett Learning,Higher LLC PEEP Strategy © Jones & Bartlett Learning, LLC Thus,NOT initial FOR Vt shouldSALE be OR 6 mL/kg. DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Moreover, strong consideration FIO2 0.3 0.3 0.3 0.3 0.3 0.4 0.4 0.5 0.5 0.5–0.8 0.8 0.9 1.0 1.0 should be given to further reducing the Vt if Pplat, adjusted for the effect PEEP 5 8 10 12 14 14 16 16 18 20 22 22 22 24 of excessive chest wall stiffness, (B) © Jones & exceedsBartlett 30 cmLearning, H2O. The LLCVt can be FIGURE 22–39 (A©) Low-PEEP Jones strategy & Bartlett used in the Learning,ARDSnet study. (LLCB) High-PEEP strategy used increased to as much as 8 mL/kg in the ARDSnet study. In each case, combinations of PEEP and FIO were used to maintain a PaO NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION2 2 if there is marked asynchrony or of 55 to 80 mm Hg or SpO2 of 88% to 95%.

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lung recruitment can be demonstrated. In the setting of mechanical disadvantage, which further worsens muscle © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC refractory hypoxemia, recruitment maneuvers may be function. Overinflated regions may also compressи и more NOT FOR SALEused, followed OR DISTRIBUTION by a level of PEEP to maintain alveolarNOT healthy FOR SALEregions ORof the DISTRIBUTION lung, impairing V/Q matching. recruitment. When setting PEEP in patients with ALI or Regions of air trapping and intrinsic PEEP also function ARDS, the hemodynamic effects of the increased intra- as a threshold load to trigger mechanical breaths. thoracic pressure should also be monitored. Noninvasive ventilation (NIV) is standard first-line © Jones & Bartlett Learning, LLCtherapy in patients with COPD© Jones and has &been Bartlett shown toLearning, LLC improve outcomes by reducing the need for endotra- Obstructive LungNOT Disease FOR SALE OR DISTRIBUTIONcheal intubation and improvingNOT survival FOR inSALE this patient OR DISTRIBUTION Respiratory failure from airflow obstruction is due to population.108 NIV has also been used in other forms of increases in airway resistance. This increases the pres- obstructive lung disease (e.g., asthma, cystic fibrosis), sure required for airflow, which may overload inspira- but there is less evidence for better outcomes in these tory© muscles,Jones &producing Bartlett a Learning,ventilatory pumpLLC failure patient populations.© Jones Invasive & Bartlett ventilatory Learning, support is LLC usu- with spontaneous minute ventilation inadequate for ally reserved for those who fail NIV or in those in whom gasNOT exchange. FOR In SALE addition, OR the DISTRIBUTION narrowed airways create NIV is contraindicated.NOT FOR SALE OR DISTRIBUTION regions of lung that cannot properly empty, and auto- Tidal volume should be sufficiently low (e.g., 6 mL/kg)

PEEP is produced. These regions of overinflation create to ensure that Pplat values are below 30 cm H2O. The dead space and put inspiratory muscles at a substantial set rate is used to control pH. However, the elevated © Jones & Bartlett Learning, LLC © Jonesairways & resistanceBartlett andLearning, the low elasticLLC recoil pressure with emphysema increase the potential for air trapping, NOT FOR SALE OR DISTRIBUTION NOTand FOR this SALE limits theOR range DISTRIBUTION of breath rates available. Per- BOX 22–6 missive hypercapnia may be an appropriate trade-off to limit overdistention. The inspiratory time in obstructive Methods for Selecting PEEP lung disease is set as low as possible to minimize the Incremental© JonesPEEP: This & approachBartlett Learning, LLCdevelopment of air trapping.© As Jones noted earlier, & Bartlett judicious Learning, LLC uses combinations of PEEP application of PEEP (up to 75% to 85% of auto-PEEP) NOT FOR SALE OR DISTRIBUTIONcan counterbalance auto-PEEPNOT to facilitate FOR SALE triggering. OR109 DISTRIBUTION and Fio2 to achieve the desired level of oxygenation or the Use of a low-density gas (e.g., helium–oxygen mix- highest compliance. tures [heliox]) is another technique that can be used to Decremental PEEP: This approach decrease auto-PEEP. © Jones begins& Bartlett with a highLearning, level of LLC © Jones & Bartlett Learning, LLC PEEP (e.g., 20 cm H O), after Neuromuscular Disease NOT FOR SALE OR DISTRIBUTION2 NOT FOR SALE OR DISTRIBUTION which PEEP is decreased in a The risk of VILI is generally less in a patient with neuro- stepwise fashion until dere- muscular failure, because lung mechanics are often near cruitment occurs, typically normal and regional overdistention is thus less likely to

with a decrease in Pao2 and occur. Higher tidal volumes may thus be used to improve © Jones & Bartlett Learning,decrease in LLC compliance. © Jonescomfort, & Bartlett maintain Learning,recruitment, LLC prevent atelectasis, NOT FOR SALE ORStress DISTRIBUTION index measurement: The NOTand FOR avoid SALE hypercarbia OR DISTRIBUTION that may adversely affect central pressure–time curve is nervous system function. However, tidal volume should observed during constant- not exceed 10 mL/kg, and Pplat should be kept below 110 flow inhalation for signs 30 cm H2O. Low levels of PEEP are often beneficial for of tidal recruitment and preventing atelectasis. If patients with neuromuscular overdistention.© Jones & Bartlett Learning, LLCdisease develop ALI or ARDS,© theyJones should & Bartlettbe managed Learning, LLC EsophagealNOT pressure FOR measure- SALE OR DISTRIBUTIONusing ventilator strategies incorporatingNOT FOR lower SALE tidal OR vol- DISTRIBUTION ment: This method estimates umes and higher levels of PEEP. the intrapleural pressure by using an esophageal balloon to Ventilatory Support Involves measure the esophageal pres- © Jones sure& Bartlett and subsequently Learning, deter- LLC Trade-Offs© Jones & Bartlett Learning, LLC NOT FORmine SALE the optimal OR DISTRIBUTION level of PEEP To provide adequateNOT FOR support SALE yet minimize OR DISTRIBUTION VILI, mechan- required. ical ventilation goals must involve trade-offs. The need Pressure–volume curve guidance: for potentially injurious ventilating pressures, volumes,

PEEP is set slightly greater and supplemental O2 must be weighed against the ben- than the lower inflection efits of better gas exchange. Accordingly, pH goals as

© Jones & Bartlett Learning,point. LLC © Joneslow as & 7.15 Bartlett and Pao Learning,2 goals as low LLC as 55 mm Hg are NOT FOR SALE OR DISTRIBUTION NOToften FOR considered SALE OR acceptable DISTRIBUTION if necessary to protect the lungs from VILI.111 Ventilator settings are thus selected

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to provide an adequate, but not necessarily normal, a low Pimax may predict respiratory muscle fatigue. © Jones &level Bartlett of gas exchangeLearning, while LLC meeting the goals of enough© JonesThe Pimax & Bartlett is measured Learning, by attachment LLC of an aner- NOT FOR SALEPEEP to OR maintain DISTRIBUTION alveolar recruitment and avoidanceNOT oid FOR manometer SALE ORto the DISTRIBUTION endotracheal or tracheostomy of a PEEP–tidal volume combination that unnecessarily tube. The patient then forcibly inhales after maximum overdistends alveoli at end-inspiration.103–106 This has led exhalation. When the Pimax is measured, it is recom- to ventilatory strategies such as permissive hypercapnia, mended that a unidirectional valve be used and that the permissive hypoxemia,© Jonesand permissive & Bartlett atelectasis. Learning, LLCairway be completely obstructed© Jones for 20 & to Bartlett 25 seconds Learning, LLC (Figure 22–41). A Pimax more negative than –20 cm NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION H2O suggests adequate inspiratory muscle strength. Liberation from Mechanical However, if the patient has high airways resistance or Ventilation An important aspect of the management of patients receiving© Jones mechanical & Bartlett ventilation Learning, is recognizing LLC when © Jones & Bartlett30 Learning, LLC theNOT patient FOR is ready SALE to be OR liberated DISTRIBUTION from the ventilator NOT FOR15 SALE45 OR DISTRIBUTION and extubating the patient at that point. Evidence-based B clinical practice guidelines have been published related 0 60 to liberation from mechanical ventilation; Box 22–7 lists the recommendations from these guidelines.112 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALERespiratory OR DISTRIBUTION Muscles NOT FOR SALE OR DISTRIBUTION For successful liberation from the ventilator, the load C placed on the respiratory muscles must be balanced by the muscles’ ability to meet that load (Figure 22–40). Respiratory muscle fatigue occurs if the load placed on the muscles is excessive,© Jones if the & musclesBartlett are Learning, weak, or LLC © Jones & Bartlett Learning, LLC if the duty cycle (theNOT inspiratory FOR SALEtime relative OR DISTRIBUTION to total NOT FOR SALE OR DISTRIBUTION cycle time) is too long. Common causes of a high load E D are high airways resistance, low lung compliance, and high minute ventilation. In addition, malposition of the diaphragm from air trapping compromises inspiratory © Jones & Bartlett Learning, LLC © Jones & BartlettA Learning, LLC muscle function. Diminished respiratory muscle func- FIGURE 22–41 The one-way valve system used to measure tionNOT may FORalso be SALE the result OR of DISTRIBUTION disease, disuse, malnu- maximum inspiratoryNOT pressure. FOR SALEThe patient OR is connected DISTRIBUTION at A, the trition, hypoxia, or electrolyte imbalance. The clinical manometer (B) is connected at C, and the patient exhales through D. signs of respiratory muscle fatigue are tachypnea, abnor- Port E is occluded during the measurement. In this way, maximum mal respiratory movements (respiratory alternans and inspiratory pressure is measured at functional residual capacity. From Kacmarek RM, Cycyk-Chapman MC, Young PJ, Romagnoli abdominal paradox), and an increase in Paco .113 © Jones & Bartlett Learning, LLC 2 © JonesDM. Determination & Bartlett of maximal Learning, inspiratory pressure:LLC a clinical study Because the maximum inspiratory pressure (Pimax) literature review. Respir Care. 1989;34:868–878. Reprinted with NOT FOR SALEis a good OR indicator DISTRIBUTION of overall respiratory muscle strength,NOT permission. FOR SALE OR DISTRIBUTION

Minute Ventilation Depressed Respiratory Drive Pain and anxiety© Jones & Bartlett Learning, LLC Sedative drugs © Jones & Bartlett Learning, LLC Sepsis NOT FOR SALE OR DISTRIBUTION Brain stem lesionNOT FOR SALE OR DISTRIBUTION Increased dead space Neuromuscular Disease Excessive feeding Load Capacity Increased Resistive Load Cervical spine injury Phrenic nerve injury Bronchospasm Critical illness polyneuropathy © JonesSecretions & Bartlett Learning, LLC © JonesProlonged & neuromuscularBartlett Learning, blockade LLC Small endotracheal tube Hyperinﬂation (COPD) NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Increased Elastic Load Malnutrition Electrolyte disturbance Low lung compliance Primary neuromuscular disease Low chest wall compliance Auto-PEEP Thoracic Wall Abnormality Flail chest © Jones & Bartlett Learning, LLC © Jones & BartlettPain Learning, LLC

NOT FOR SALE ORFIGURE DISTRIBUTION 22–40 Respiratory muscle performance is determinedNOT FOR by the balanceSALE between OR DISTRIBUTIONthe load that is placed on the respiratory muscles and the ability of the muscles to meet that load.

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BOX 22–7 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OREvidence-Based DISTRIBUTION Guidelines for DiscontinuingNOT Ventilatory FOR SALE Support OR DISTRIBUTION Recommendation 1: In patients requiring mechanical ventilation for more than 24 hours, a search for all the causes that may be contributing to ventilator dependence should be undertaken. This is particularly true in the patient who has failed attempts at withdrawing the mechanical ventilator. Reversing© Jones all possible & Bartlett ventilatory Learning, and nonventilatory LLC issues should be an integral© Jones part of & the Bartlett venti- Learning, LLC lator discontinuation process. RecommendationNOT FOR 2: Patients SALE receiving OR DISTRIBUTION mechanical ventilation for respiratory failureNOT should FOR undergoSALE OR DISTRIBUTION a formal assessment of discontinuation potential if the following criteria are satisfied: (1) evidence for some reversal of the underlying cause for respiratory failure, (2) adequate oxygenation and pH, (3) hemodynamic stability, and (4) the capability to initiate an inspiratory effort. © JonesRecommendation & Bartlett 3Learning,: Formal discontinuation LLC assessments for patients© Jones receiving & mechanicalBartlett Learning, ventilation for LLC respiratory failure should be performed during spontaneous breathing rather than while the patient is NOT FORstill SALE receiving OR substantial DISTRIBUTION ventilatory support. An initial briefNOT period FOR of spontaneous SALE OR breathing DISTRIBUTION can be used to assess the capability of continuing onto a formal spontaneous breathing trial (SBT). The criteria with which to assess patient tolerance during SBTs are the respiratory pattern, the adequacy of gas exchange, hemodynamic stability, and subjective comfort. The tolerance of SBTs lasting 30 to 120 © Jones & Bartlett Learning,minutes should LLC prompt consideration for ©permanent Jones ventilator& Bartlett discontinuation. Learning, LLC Recommendation 4: The removal of the artificial airway from a patient who has successfully been NOT FOR SALE OR DISTRIBUTIONdiscontinued from ventilatory support shouldNOT beFOR based SALE on assessments OR DISTRIBUTION of airway patency and the ability of the patient to protect the airway. Recommendation 5: Patients receiving mechanical ventilation for respiratory failure who fail an SBT should have the cause for the failed SBT determined. Once reversible causes for failure are corrected,© subsequent Jones & SBTs Bartlett should Learning, be performed LLC every 24 hours. © Jones & Bartlett Learning, LLC Recommendation 6: Patients receiving mechanical ventilation for respiratory failure who fail an SBT shouldNOT receive FOR a stable, SALE nonfatiguing, OR DISTRIBUTION comfortable form of ventilatory supportNOT. FOR SALE OR DISTRIBUTION Recommendation 7: Anesthesia/sedation strategies and ventilator management aimed at early extubation should be used in postsurgical patients. Recommendation 8: Weaning/discontinuation protocols that are designed for nonphysician health- © Jones care& Bartlett professionals Learning, should be LLC developed and implemented ©by Jonesintensive & care Bartlett units. Protocols Learning, aimed LLC at optimizing sedation also should be developed and implemented. NOT FORRecommendation SALE OR 9 :DISTRIBUTION Tracheostomy should be considered after anNOT initial FOR period SALE of stabilization OR DISTRIBUTION on the ventilator when it becomes apparent that the patient will require prolonged ventilator assistance. Tracheostomy then should be performed when the patient appears likely to gain one or more of the benefits ascribed to the procedure. Patients who may derive particular benefit from early tracheostomy are the following: those requiring high levels of sedation to tolerate a translaryngeal tube; © Jones & Bartlett Learning,those with LLCmarginal respiratory mechanics© (often Jones manifested & Bartlett as tachypnea) Learning, in whom LLC a tracheostomy NOT FOR SALE OR DISTRIBUTIONtube having lower resistance might reduceNOT the risk FOR of muscle SALE overload; OR DISTRIBUTION those who may derive psy- chological benefit from the ability to eat orally, communicate by articulated speech, and experience enhanced mobility; and those in whom enhanced mobility may assist physical therapy efforts. Recommendation 10: Unless there is evidence for clearly irreversible disease (e.g., high spinal cord injury or advanced amyotrophic lateral sclerosis), a patient requiring prolonged mechanical ventilatory© support Jones for &respiratory Bartlett failure Learning, should not LLC be considered permanently© ventilator Jones dependent& Bartlett Learning, LLC until 3NOT months FOR of ventilator SALE liberationOR DISTRIBUTION attempts have failed. NOT FOR SALE OR DISTRIBUTION Recommendation 11: Critical care practitioners should familiarize themselves with facilities in their com- munities, or units in hospitals they staff, that specialize in managing patients who require prolonged dependence on mechanical ventilation. Such familiarization should include reviewing published © Jones &peer-reviewed Bartlett Learning, data from those LLC units, if available. When medically© Jones stable & for Bartlett transfer, patients Learning, who LLC have failed ventilator discontinuation attempts in the intensive care unit should be transferred to NOT FORthose SALE facilities OR that DISTRIBUTION have demonstrated success and safety inNOT accomplishing FOR SALE ventilator OR discontinuation. DISTRIBUTION Recommendation 12: Ventilator liberation strategies in the prolonged mechanical ventilation patient should be slow paced and should include gradually lengthening self-breathing trials. Modified from MacIntyre NR, Cook DJ, Ely EW Jr, et al. Evidence-based guidelines for weaning and discontinuing ventilatory sup- © Jones & Bartlettport: Learning, a collective task LLCforce facilitated by the American College© Jones of Chest Physicians; & Bartlett the American Learning, Association LLC for Respiratory Care; and the American College of Critical Care Medicine. Chest. 2001;120:375S–396S NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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low compliance, a Pimax of –20 cm H2O may not be where Pbreath is the pressure required to generate a © Jones &adequate Bartlett for Learning, unassisted breathing. LLC © Jonesspontaneous & Bartlett breath. Learning, The Pbreath LLC can be determined NOT FOR SALEThe respiratoryOR DISTRIBUTION muscles should be rested if fatigueNOT with FOR esophageal SALE ORballoon DISTRIBUTION measurements during a short occurs, and a rest period of 24 hours or longer may be trial of spontaneous breathing. required.114 Respiratory muscle rest usually is provided by ventilatory support high enough to provide patient Assessing Readiness for Liberation comfort and still allow© Jonessome inspiratory & Bartlett efforts. Learning, Impor- LLCA number of factors should© beJones improved & Bartlett before anLearning, LLC tantly, total rest (i.e., no inspiratory muscle activity with attempt is made to liberate the patient from the ventilator controlled mechanicalNOT ventilation) FOR SALE can also OR be DISTRIBUTIONharmful, NOT FOR SALE OR DISTRIBUTION (Box 22–8). Weaning parameters117,118 often are used to because muscle atrophy has been shown to develop in as assess liberation potential and are divided into two cat- 98 If respiratory little as 24 hours under these conditions. egories: parameters affected by lung mechanics, and gas muscle fatigue is the result of an excessive load, the load exchange parameters. The spontaneous Vt (Ͼ 5 mL/kg), should be reduced before attempts are made to liberate © Jones & Bartlett Learning, LLC respiratory ©rate Jones (Ͻ 30 breaths/min),& Bartlett Learning,minute ventilation LLC the patient from the ventilator. This is done with provi- NOT FOR SALE OR DISTRIBUTION (Ͻ 12 L/min),NOT vital FORcapacity SALE (Ͼ 15 mL/kg),OR DISTRIBUTION and the Pimax sion of therapy that can increase lung compliance or Ͻ ( –20 cm H2O) have been used as predictors of success. reduce airways resistance. The rapid shallow breathing index (RSBI)119 is calculated The tension–time index has been used to predict by division of the spontaneous respiratory rate by the Figure 22–42).115 The tension– diaphragmatic fatigue ( Vt (in liters). An RSBI less than 105 has been used as time index is calculated as the product of the contractile © Jones & Bartlett Learning, LLC © Jonespredictive & Bartlett of successful Learning, ventilator liberation,LLC and an RSBI force (Pdi/Pdi–max) and contraction duration (duty greater than 105 has been used to predict failure. An NOT FOR SALEcycle, Ti/Ttot). OR DISTRIBUTION This requires measurement of the meanNOT FOR SALE OR DISTRIBUTION increase in Vd/Vt (which should be less than 0.6) and an transdiaphragmatic pressure (Pdi), the transdiaphrag- и и increase in Vco2 and Vo2 imply an increased ventilatory matic pressure with maximum inhalation (Pdi–max), requirement. the inspiratory time (Ti), and the total respiratory cycle Despite the many weaning parameters that have been time (Ttot). A tension-time© Jones index & Bartlettover 0.15 Learning,is predic- LLCreported, however, no criterion© Jones is better & atBartlett predicting Learning, LLC tive of respiratory muscle fatigue. Measurement of the extubation readiness than a spontaneous breathing trial transdiaphragmatic NOTpressure FOR requires SALE esophageal OR DISTRIBUTION and NOT FOR SALE OR DISTRIBUTION (SBT) with an integrated assessment focusing on the gastric pressure measurements, which are almost never respiratory pattern, gas exchange, hemodynamics, and performed in mechanically ventilated patients. A simpler comfort. In fact, overreliance on weaning parameters form of tension-time index is the pressure–time index 116 (PTI),© Jones which & can Bartlett be determined Learning, more LLC readily with © Jones & Bartlett Learning, LLC equipment available in the critical care unit. It is calcu- BOX 22–8 latedNOT as follows: FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION PTI ϭ (Pbreath/Pimax) ϫ (Ti/Ttot) Criteria Assessed to Determine Readiness for Ventilator Discontinuation (Liberation) © Jones & Bartlett Learning, LLC © Jones & BartlettEvidence Learning,for some reversal LLC of the NOT FOR SALE OR1.0 DISTRIBUTION NOT FOR SALEunderlying OR DISTRIBUTION cause for respiratory failure Adequate oxygenation (e.g., 0.8 Fatigue threshold Ͼ Pao2/Fio2 ratio 150 to 200; PEEP 5 to 8 cm H O; 0.6 Fatigue zone 2

tot Յ © Jones & Bartlett Learning, LLC Fio2 0.4 to 0.5)© Jonesand pH & Bartlett Learning, LLC Ͼ / T I NOT FOR SALE OR DISTRIBUTION (e.g., 7.25) NOT FOR SALE OR DISTRIBUTION T 0.4 Hemodynamic stability, as defined by the absence of 0.2 Nonfatigue T Tdi zone active myocardial ischemia and the absence of clinically © Jones0 & Bartlett Learning, LLC © Jonessignificant & hypotensionBartlett Learning, (i.e., LLC NOT FOR SALE0.2 OR0.4 DISTRIBUTION0.6 0.8 1.0 NOTrequiring FOR noSALE vasopressor OR DISTRIBUTION Pdi/Pdi–max therapy or therapy with only FIGURE 22–42 Tension-time index; note that the low-dose vasopressors) fatigue threshold is a tension-time index of about The capability to initiate an inspi- 0.15 to 0.18. From Grassino A, Macklem PT. Respiratory muscle fatigue and ventilatory failure. ratory effort © Jones & BartlettAnn RevLearning, Med. 1984;35:625–647. LLC Reprinted with © Jones & Bartlett Learning, LLC NOT FOR SALE permission.OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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may result in prolonged stay on the ventilator.120 It also studies allowed performance of the SBT with the patient © Jones &is Bartlett important Learning, to reduce or LLCtemporarily discontinue seda-© Jonesattached & Bartlettto the ventilator. Learning,124–126 LLC NOT FOR SALEtion in ORpreparation DISTRIBUTION of ventilator liberation; this hasNOT FORThe SBTSALE can ORbe performed DISTRIBUTION with no positive pressure been reported to decrease both days of ventilation and applied to the airway, with a low level of CPAP (5 cm 100,121 mortality. H2O), or with a low level of PSV (5 to 8 cm H2O). Pro- ponents of the CPAP approach argue that this maintains Approaches to Liberation© Jones & Bartlett Learning, LLCfunctional residual capacity at© a Joneslevel similar & Bartlett to that after Learning, LLC extubation. It is argued that, in a patient with obstructive Two prospective, randomized, controlled trials com- NOT FOR SALE OR DISTRIBUTIONlung disease, this low level NOTof CPAP FOR maintains SALE airway OR DISTRIBUTION pared SIMV weaning (i.e., gradual reduction in manda- patency if the patient cannot control exhalation because tory breath rate), PSV weaning (i.e., gradual reduction in of the presence of the artificial airway. In patients with the level of PSV), and daily (or twice daily) SBT.122,123 In marginal left ventricular function, however, a low level these studies, after meeting screening criteria, an SBT of positive intrathoracic pressure may support the failing was© performed. Jones & Both Bartlett studies Learning, reported that LLC the major- © Jones & Bartlett Learning, LLC heart. Such patients may tolerate a CPAP trial but then ity of patients were successfully extubated after the first NOT FOR SALE OR DISTRIBUTION develop congestiveNOT FOR heart SALEfailure when OR extubated.DISTRIBUTION34 Also, SBT. In those who failed the initial SBT, no difference in a low level of CPAP may counterbalance auto-PEEP in outcome (duration of ventilation) was seen between the patients with COPD, resulting in a successful SBT, but T piece and PSV methods. However, both the SBT and respiratory failure soon after extubation. PSV methods were superior to SIMV in both studies. © Jones & Bartlett Learning, LLC © JonesProponents & Bartlett of the Learning, low-level LLCPSV approach argue Although newer-generation ventilators feature modes that this overcomes the resistance to breathing through NOT FOR SALEintended OR to facilitate DISTRIBUTION weaning (e.g., SmartCare, adaptiveNOT the FOR artificial SALE airway. OR DISTRIBUTIONHowever, this argument fails to support ventilation, volume support), evidence is lacking recognize that the upper airway of an intubated patient that these modes hasten ventilator liberation compared typically is swollen and inflamed, such that, at least in with use of a daily SBT. one study, the resistance through the upper airway after The traditional approach to an SBT uses a T piece, © Jones & Bartlett Learning, LLCextubation was similar to that© seen Jones with the & endotrachealBartlett Learning, LLC in which the patient is removed from the ventilator, tube in place.127 Resistance through the artificial airway and humidified supplementalNOT FOR SALEoxygen ORis provided. DISTRIBUTION is affected by many factors, includingNOT FOR the patient’s SALE inspi-OR DISTRIBUTION Humidified gas typically is provided as a heated or cool ratory flow, the inner diameter of the tube, whether the aerosol of water from a large-volume nebulizer. For tube is an endotracheal or tracheostomy tube, and the patients with reactive airways, this aerosol may induce presence of secretions in the tube. This makes it difficult bronchospasm. In such cases a humidification system © Jones & Bartlett Learning, LLC to choose an© Jonesappropriate & Bartlett level of pressure Learning, support LLC to that does not generate an aerosol should be used, such overcome tube resistance. However, one study reported as NOTa heated FOR passover SALE humidifier. OR DISTRIBUTION Passive humidifiers similar outcomesNOT whenFOR the SALE SBT was OR performed DISTRIBUTION with a T (e.g., artificial noses, heat and moisture exchangers) 128 piece and with 7 cm H2O PSV. Similar outcomes of an should be avoided because of their dead space and SBT have also been reported with or without the use of resistive workload. tube compensation during an SBT.62 The SBT can be RESPIRATORY RECAP Similar outcomes are likely with a 2-hour SBT or a © Jones & Bartlett Learning, LLC conducted with-© Jones30-minute & Bartlett SBT.129 In Learning, the acute care LLC setting, tolerance of NOT FOR SALELiberation OR DISTRIBUTION from Mechanical out removal ofNOT an FOR SBT ofSALE 30 minutes OR DISTRIBUTIONto 2 hours duration should prompt Ventilation the patient from consideration for extubation. For chronically ventilator- » Regularly assess for the ventilator, and liberation readiness. dependent patients with a tracheostomy, the length of this approach has each SBT is increased, with alternating periods of ven- » Perform a spontaneous several advan- breathing trial to assess tilatory support and SBT. In this case, the goal may be readiness for extubation.© Jones & Bartletttages. NoLearning, addi- LLCdaytime liberation with nocturnal© Jones ventilation. & Bartlett Learning, LLC » If a spontaneousNOT breathing FOR SALEtional OR equipment DISTRIBUTION NOT FOR SALE OR DISTRIBUTION trial is not tolerated, assess is required, and Recognition of a Failed Spontaneous for causes of failure. if the patient fails » Do not use synchronized the SBT, ventila- Breathing Trial intermittent mechanical tory support can A failed SBT is discomforting for the patient and may ventilation (SIMV) as a © Jonesweaning &mode. Bartlett Learning,be quicklyLLC rees- induce significant© Jones cardiopulmonary & Bartlett distress.Learning, Commonly LLC NOT» Use FOR protocols SALE to improve OR DISTRIBUTIONtablished. All the listed criteriaNOT for discontinuation FOR SALE of OR an SBT DISTRIBUTION include tachy- successful liberation. monitoring func- pnea (respiratory rate over 35 breaths/min for 5 minutes

tions and alarms or longer); hypoxemia (Spo2 below 90%); tachycardia on the ventilator are available during the SBT, which (heart rate over 140 beats/min or a sustained increase may allow prompt recognition that the patient is failing above 20%); bradycardia (sustained decrease in the heart © Jones & theBartlett SBT. Most Learning, of the literature LLC related to ventilator lib-© Jonesrate of & over Bartlett 20%); hypertensionLearning, LLC(systolic blood pres- NOT FOR SALEeration studiesOR DISTRIBUTION using a traditional SBT, although severalNOT sure FOR over SALE 180 mmOR Hg);DISTRIBUTION hypotension (systolic blood

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pressure under 90 mm Hg); and agitation, diaphore- © Jones &sis, Bartlett or anxiety. Learning, In some patients LLC the last three factors © FullJones or partial & ventilatory Bartlett support Learning, LLC Comfort NOT FOR SALEare not caused OR DISTRIBUTION by SBT failure and can be appropriately NOT FOR SALE OR DISTRIBUTION treated with verbal reassurance or pharmacologic Disease resolution support. When SBT failure is recognized, ventilatory Determine Adequate gas exchange Assess readiness cause of support should be promptly reestablished. Hemodynamic stability failure © Jones & Bartlett Learning, LLC Ability to breathe© Jones & Bartlett Learning, LLC Causes of Spontaneous Breathing NOT FOR SALE OR DISTRIBUTION NOTFail FOR SALE OR DISTRIBUTION Trial Failure Spontaneous breathing trial When an SBT fails, the reason should be identified and corrected before another SBT is performed. Success There are a variety of physiologic and technical rea- Upper airway patent? sons© why Jones patients & failBartlett an SBT. AnLearning, excessive respiratory LLC Evaluate for extubation© Jones Aspiration& Bartlett risk? Learning, LLC Able to clear secretions? muscleNOT load FOR may beSALE the cause. OR High DISTRIBUTION airways resistance NOT FOR SALE OR DISTRIBUTION and low compliance contribute to the increased effort necessary to breathe. Auto-PEEP may delay liberation Extubate or trach in patients with COPD, because it increases the pleural pressure needed to initiate inhalation. Electrolyte FIGURE 22–43 An evidence-based approach to ventilator discontinuation © Jones & imbalanceBartlett mayLearning, cause respiratory LLC muscle weakness. ©and Jones extubation. & Bartlett Learning, LLC NOT FOR SALEInadequate OR levels DISTRIBUTION of potassium, magnesium, phos- NOT FOR SALE OR DISTRIBUTION phate, and calcium impair ventilatory muscle function. Appropriate nutritional support often improves therapists and nurses. Studies have reported improved the ventilator discontinuation process, but care should outcomes when protocols are used.124–126,134,135 Fig- be taken to avoid overfeeding, because excessive caloric ure 22–43 presents the elements of an effective protocol. ingestion elevates carbon© Jones dioxide & production. Bartlett Learning,Failure of LLCFrom these elements incorporating© Jones best & Bartlettevidence, Learning,a LLC any major organ systemNOT can FOR result SALE in failure OR to DISTRIBUTION liberate specific protocol can be developedNOT FORthat meets SALE the ORlocal DISTRIBUTION the patient from the ventilator. Fever and infection are culture of the ICU. Note that the use of an SBT is central of particular concern because they increase both oxygen to the protocol. consumption and carbon dioxide production, resulting in an increased ventilatory requirement. Cardiac dysfunction© can Jones delay liberation & Bartlett until Learning,appropriate management LLC of KEY POINTS© Jones & Bartlett Learning, LLC cardiovascular status has occurred. NOT FOR SALE OR DISTRIBUTION • EffortsNOT should FOR be SALE made to OR avoid DISTRIBUTION complications Once the patient has been judged to no longer need during mechanical ventilation. mechanical ventilatory support, attention then turns to • Forms of ventilator-induced lung injury include the need for the artificial airway. This requires a different alveolar overdistention and repetitive opening set of assessments that focus on the patient’s ability to and closing. protect the natural airway. Key parameters include cough © Jones & Bartlett Learning, LLC © Jones• &Volume Bartlett control Learning, ventilation LLC maintains minute strength and the need for suctioning (i.e., suctioning NOT FOR SALE OR DISTRIBUTION NOT FOR ventilationSALE OR but DISTRIBUTION allows airway pressure and plateau requirements exceeding every 2 hours should preclude pressure to fluctuate. extubation). Although the ability to follow commands is • Pressure control ventilation allows minute venti- desirable before extubation, it is not essential in patients lation to fluctuate, but airway pressure is limited otherwise able to protect the airway. to the peak pressure set on the ventilator. In appropriately selected patients (e.g., those recover- © Jones & Bartlett Learning, LLC• Modes on modern ventilators© Jones include & Bartlett continuous Learning, LLC ing from a COPD exacerbation), extubation to NIV may NOT FOR SALE OR DISTRIBUTIONmandatory ventilation,NOT synchronized FOR SALE intermit- OR DISTRIBUTION reduce the duration of mechanical ventilation.130–132 Extu- tent mandatory ventilation, pressure support bation to NIV can also be considered to prevent extuba- ventilation, continuous positive airway pressure, tion failure in patients at risk, such as those with COPD, adaptive pressure control, adaptive support ven- cardiac disease, or others at risk for extubation failure. tilation, airway pressure release ventilation, tube However, NIV is generally not recommended to rescue © Jones & Bartlett Learning, LLC compensation,© Jones &proportional Bartlett Learning,assist ventilation, LLC a failed extubation.133,134 If the patient fails extubation, NOT FOR SALE OR DISTRIBUTION neurallyNOT adjusted FOR SALE ventilatory OR DISTRIBUTIONassist, and high- consideration should be given to emergent reintubation. frequency oscillatory ventilation. • The tidal volume should be set to avoid overdis- Ventilator Discontinuation (Weaning) tention lung injury: 6 mL/kg PBW is a suggested Protocols initial setting. © Jones & VentilatorBartlett Learning,discontinuation LLC (weaning) protocols have© Jones• &The Bartlett respiratory Learning, rate and I:E LLC ratio are set to con- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION become increasingly popular in recent years, and these trol the Paco2 and to avoid hemodynamic com- protocols typically are implemented by respiratory promise and auto-PEEP.

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14. Webb HJH, Tierney DF. Experimental pulmonary edema due • The Fio2 initially should be set at 1 and then © Jones & Bartlett Learning, LLC © Jonesto & intermittent Bartlett positive Learning, pressure ventilation LLC with high inflation weaned per pulse oximetry to maintain an Spo2 NOT FOR SALEover OR 88%. DISTRIBUTION NOT FORpressures: SALE protection OR DISTRIBUTION by positive end-expiratory pressure. Am Rev Respir Dis. 1974;110:556–565. • PEEP should be set to avoid alveolar derecruit- 15. Crotti S, Mascheroni D, Caironi P, et al. Recruitment and dere- ment for patients with ARDS and to counterbal- cruitment during acute respiratory failure. Am J Respir Crit Care ance auto-PEEP in patients with COPD. Med. 2001;164:131–140. • The following should be monitored in the 16. Mead J, Takishima T, Leith D. Stress distribution in lungs: a © Jones & Bartlett Learning, LLC model of pulmonary elasticity.© J ApplJones Physiol &. 1970;28:596–608. Bartlett Learning, LLC mechanically ventilated patient: physical signs NOT FOR SALE OR DISTRIBUTION17. Chiumello D, Carlesso E, CadringherNOT FOR P, et al. SALE Lung stress OR and DISTRIBUTION and symptoms, blood gas measurements, lung strain during mechanical ventilation for acute respiratory dis- mechanics, hemodynamics, patient–ventilator tress syndrome. Am J Respir Crit Care Med. 2008;178:346–355. synchrony, and sedation. 18. Vaporidi K, Voloudakis G, Priniannakis G, et al. Effects of • The most important aspect of liberation respiratory rate on ventilator-induced lung injury at a constant Paco in a mouse model of normal lung. Crit Care Med. from mechanical ventilation is assessment for 2 © Jones & Bartlett Learning, LLC 2008;36:1277–1283.© Jones & Bartlett Learning, LLC readiness. 19. Rich BR, Reickert CA, Sawada S, et al. Effect of rate and •NOT A spontaneousFOR SALE breathing OR DISTRIBUTION trial identifies most inspiratoryNOT flow FOR on ventilator SALE induced OR lung DISTRIBUTION injury. J Trauma. patients who are ready for liberation from 2000;49:903–911. mechanical ventilation. 20. Marini JJ, Hotchkiss JR, Broccard AF. Bench-to-bedside review: • The poorest outcomes from the ventilator discon- microvascular and airspace linkage in ventilator-induced lung injury. Crit Care (London). 2003;7:435–444. © Jones & Bartletttinuation Learning, process haveLLC been reported with SIMV.© Jones21. Trembly& Bartlett L, Valenza Learning, F, Ribiero SP, Li LLCJ, Slutsky AS. Injurious ven- • For patients who do not tolerate a spontane- tilatory strategies increase cytokines and C-fos M-RNA expres- NOT FOR SALE ousOR breathing DISTRIBUTION trial, ventilatory support shouldNOT FORsion SALE in an isolated OR rat DISTRIBUTION lung model. J Clin Invest. 1997;99:944–952. be reestablished and the cause of the failure 22. Ranieri VM, Suter PM, Tortorella C, et al. Effect of mechanical identified. ventilation on inflammatory mediators in patients with acute respiratory distress syndrome: a randomized controlled trial. JAMA. 1999;282:54–61. © Jones & Bartlett Learning, LLC23. Slutsky AS, Trembly L. Multiple© system Jones organ & failure: Bartlett is mechan- Learning, LLC REFERENCES ical ventilation a contributing factor? Am J Respir Crit Care Med. 1. Pierson DJ. IndicationsNOT for mechanicalFOR SALE ventilation OR in adultsDISTRIBUTION with 1998;157:1721–1725. NOT FOR SALE OR DISTRIBUTION acute respiratory failure. Respir Care. 2002;47:249–265. 24. Nahum A, Hoyt J, Schmitz L, et al. Effect of mechanical ventila- 2. Matlu GM, Factor P. Complications of mechanical ventilation. tion strategy on dissemination of intertracheally instilled E coli Respir Care Clin North Am. 2000;6:213–252. in dogs. 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36. MacIntyre NR, McConnell R, Cheng KG, et al. Patient-venti- egy for acute respiratory distress syndrome? Anesthesiology. © Jones & Bartlettlator flow Learning, dyssynchrony: LLC flow-limited versus pressure-limited© Jones2009;111:863–870. & Bartlett Learning, LLC NOT FOR SALEbreaths. OR Crit DISTRIBUTION Care Med. 1997;25:1671–1677. NOT 58.FOR Gut SALEtmann J, ORHaberthür DISTRIBUTION C, Mols G, Lichtwarck-Aschoff M. 37. MacIntyre NR, Sessler CN. Are there benefits or harm from Automatic tube compensation (ATC). Minerva Anesthesiol. pressure targeting during lung-protective ventilation? Respir 2002;68:369–377. Care. 2010;55:175–180. 59. Cohen JD, Shapiro M, Grozovski E, et al. Extubation outcome 38. Branson RD, Chatburn RL. Technical description and clas- following a spontaneous breathing trial with automatic tube sification of modes of ventilator operation. Respir Care. compensation versus continuous positive airway pressure. 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Marantz© S, JonesPatrick W, &Webster Bartlett K, et al. Learning,Response of ventilator- LLC support ventilation. Respir Care. 2005;50:166–186. dependent patients to different levels of proportional assist. J 43.NOT Jubran FOR A, Van SALE de Graaff ORWB, TobinDISTRIBUTION MJ. Variability of patient- Appl PhysiolNOT. 1996;80:397–403. FOR SALE OR DISTRIBUTION ventilator interaction with pressure support ventilation in 63. Gay PC, Hess DR, Hill NS. Noninvasive proportional assist patients with chronic obstructive pulmonary disease. Am J ventilation for acute respiratory insufficiency. Comparison Respir Crit Care Med. 1995;152:129–136. with pressure support ventilation. Am J Respir Crit Care Med. 44. Parthasarathy S, Jubran A, Tobin MJ. Cycling of inspiratory and 2001;164:1606–1611. © Jones & Bartlettexpiratory Learning, muscle groups LLC with the ventilator in airflow limita-© Jones64. Bosma& Bartlett K, Ferreyra Learning,G, Ambrogio C, etLLC al. Patient-ventilator inter- tion. 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Does high-frequency ventilation offer benefits over generation during synchronized© Jones intermittent& Bartlett mechanical Learning, venti- LLC conventional ventilation in adult© Jonespatients with & acute Bartlett respiratory Learning, LLC lation: effect of machineNOT assistance FOR onSALE breathing OR effort. DISTRIBUTION Am Rev distress syndrome? Respir CareNOT. 2007;52:595–608. FOR SALE OR DISTRIBUTION Respir Dis. 1988;138:1169–1179. 67. Branson RD, Campbell RS, Davis D, et al. Comparison of pres- 48. Leung P, Jubran A, Tobin MJ. Comparison of assisted ventilator sure and flow triggering systems during continuous positive modes on triggering, patient effort, and dyspnea. Am J Respir airway pressure. Chest. 1994;106:540–544. Crit Care Med. 1997;155:1940–1948. 68. Goulet RL, Hess D, Kacmarek RM. Flow versus pressure 49. Branson RD, Chatburn RL. Controversies in the critical care triggering in mechanically ventilated adult patients. 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Bartlett J Intensive Learning, Care Med. LLC1988;65:1488–1499. © Jones & Bartlett Learning, LLC 2009;24:122–130. 74. Petrof BJ, Lagare M, Goldberg P, et al. Continuous positive 54. Gruber PC, GomersallNOT CD, FOR Leung PE,SALE et al. Randomized OR DISTRIBUTION con- airway pressure reduces workNOT of breathing FOR and SALE dyspnea duringOR DISTRIBUTION trolled trial comparing adaptive-support ventilation with weaning from mechanical ventilation in severe chronic obstruc- pressure-regulated volume-controlled ventilation with auto- tive pulmonary disease. Am Rev Respir Dis. 1990;141:281–289. mode in weaning patients after cardiac surgery. Anesthesiology. 75. Tobin MJ, Lodato RF. PEEP, auto-PEEP, and waterfalls. Chest. 2008;109:81–87. 1989;96:449–451. 55.© TassauxJones D, &Dalmas Bartlett E, Gratadour Learning, P, Jolliet P. Patient-ventilatorLLC 76. Hoit JD,© Banzett Jones RB, &Lohmeier Bartlett HL, etLearning, al. 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JAMA. 2010;303:865–873. © ratoryJones pressure. & BartlettAm J Respir Crit Learning, Care Med. 2007;176:761–767. LLC 106. Mercat ©A, RichardJones JC, & Vi elleBartlett B, et al. PositiveLearning, end-expiratory LLC 85. Benditt JO. Esophageal and gastric pressure measurements. pressure setting in adults with acute lung injury and acute respi- NOTRespir FOR Care. 2005;50:68–77. SALE OR DISTRIBUTION ratory distressNOT syndrome: FOR SALE a randomized OR controlled DISTRIBUTION trial. JAMA. 86. Talmor D, Sarge T, Malhotra A, et al. Mechanical ventilation 2008;299:646–655. guided by esophageal pressure in acute lung injury. N Engl J Med. 107. Suter PM, Fairley HB, Isenberg MD. Optimic end expiratory 2008;359:2095–2104. pressure in patients with acute pulmonary failure. N Engl J Med. 87. Hager DN, Brower RG. Customizing lung-protective mechani- 1975;292:284–289. © Jones & Bartlettcal ventilation Learning, strategies. LLCCrit Care Med. 2006;34:1554–1555. © Jones108. Nava & Bartlett S, Hill N. Non-invasive Learning, ventila LLCtion in acute respiratory 88. Talmor DS, Fessler HE. Are esophageal pressure measure- failure. Lancet. 2009;374:250–259. NOT FOR SALEments OR important DISTRIBUTION in clinical decision-making in mechanicallyNOT 109. FOR Medoff SALE BD. Invasive OR DISTRIBUTIONand noninvasive ventilation in patients with ventilated patients? Respir Care. 2010;55:162–172. asthma. Respir Care. 2008;53:740–750. 89. Hess DR, Bigatello LM. The chest wall in acute lung injury/ 110. Mascia L, Zavala E, Bosma K, et al. High tidal volume is associ- acute respiratory distress syndrome. Curr Opin Crit Care. 2008; ated with the development of acute lung injury after severe brain 14:94–102. injury: an international observational study. Crit Care Med. 90. Dhand R. Ventilator graphics and respiratory mechan- 2007;35:1815–1820. ics in the patient ©with Jones obstructive & lungBartlett disease. RespirLearning, Care. LLC111. Hickling KG, Walsh J, Henderson© Jones S, Jackson & R. Bartlett Low mortality Learning, LLC 2005;50:246–261. NOT FOR SALE OR DISTRIBUTIONrate in adult respiratory distressNOT syndrome FOR using SALE low-volume, OR DISTRIBUTION 91. de Wit M, Miller KB, Green DA, et al. Ineffective triggering pressure-limited ventilation with permissive hypercapnia: a pro- predicts increased duration of mechanical ventilation. Crit Care spective study. Crit Care Med. 1994;22:1568–1578. Med. 2009;37:2740–2745. 112. MacIntyre NR, Cook DJ, Ely EW Jr, et al. Evidence-based guide- 92. Thille AW, Rodriguez P, Cabello B, et al. Patient-ventilator asyn- lines for weaning and discontinuing ventilatory support: a col- chrony during assisted mechanical ventilation. Intensive Care lective task force facilitated by the American College of Chest © MedJones. 2006;32:1515–1522. & Bartlett Learning, LLC Physicians;© Jones the American & Bartlett Association Learning, for Respiratory LLC Care; 93.NOT Imanaka FOR H, NishimuraSALE OR M, Takeuchi DISTRIBUTION M, et al. Autotrigger- and theNOT American FOR College SALE of Critical OR Care DISTRIBUTION Medicine. Chest. ing caused by cardiogenic oscillation during flow-triggered 2001;120(6 suppl):375S–395S. mechanical ventilation. Crit Care Med. 2000;28:402–407. 113. Cohen CA, Zagelbaum G, Gross D, et al. Clinical manifestations 94. Yang LY, Huang YC, Macintyre NR. Patient-ventilator synchrony of inspiratory muscle fatigue. Am J Med. 1982;73:308–316. during pressure-targeted versus flow-targeted small tidal vol- 114. Laghi F, D’Alfonso N, Tobin MJ. Pattern of recovery from dia- ume assisted ventilation. J Crit Care. 2007;22:252–257. phragmatic fatigue over 24 hours. J Appl Physiol. 1995;79:539–546. © Jones & Bartlett95. Kallet RH, Learning, Campbell AR, LLC Dicker RA, et al. Work of breathing© Jones115. St &oller Bartlett JK. Physiologic Learning, rationale forLLC resting the ventilatory during lung-protective ventilation in patients with acute lung muscles. Respir Care. 1991;36:290–296. NOT FOR SALEinjury OR and DISTRIBUTION acute respiratory distress syndrome: a comparisonNOT 116. FOR Jabour SALE ER, Rabil OR DM, DISTRIBUTION Truwitt JD, et al. Evaluation of a new wean- between volume and pressure-regulated breathing modes. ing index based on ventilatory endurance and the efficiency of Respir Care. 2005;50:1623–1631. gas exchange. Am Rev Respir Dis. 1991;144:531–537. 96. Hess DR, Thompson BT. Patient-ventilator dyssynchrony during 117. Epstein SK. Weaning parameters. Respir Care Clin North Am. lung protective ventilation: what’s a clinician to do? Crit Care 2000;6:253–301. Med. 2006;34:231–233.© Jones & Bartlett Learning, LLC118. Meade M, Guyatt G, Cook© D, Joneset al. Predicting & Bartlett success inLearning, LLC 97. Branson RD, Johannigman JA. The role of ventilator graphics weaning from mechanical ventilation. Chest. 2001;120(6 when setting dual-controlNOT modes. FOR Respir SALE Care. 2005;50:187–201.OR DISTRIBUTIONsuppl):400S–424S. NOT FOR SALE OR DISTRIBUTION 98. Levine S, Nguyen T, Taylor N, et al. Rapid disuse atrophy of dia- 119. Yang KL, Tobin MJ. A prospective study of indices predicting phragm fibers in mechanically ventilated humans. N Engl J Med. the outcome of trials of weaning from mechanical ventilation. N 2008;358:1327–1335. Engl J Med. 1991;324:1445–1450. 99. Hermans G, De Jonghe B, Bruyninckx F, Van den Berghe G. 120. Tanios MA, Nevins ML, Hendra KP, et al. A randomized, con- © ClinicalJones review: & Bartlett critical illness Learning, polyneuropathy LLC and myopathy. trolled trial© Jones of the role &of weaningBartlett predictors Learning, in clinical decision LLC Crit Care. 2008;12:238. making. Crit Care Med. 2006;34:2530–2535. 100.NOT Girard FOR TD, Kress SALE JP, Fuchs OR BD, DISTRIBUTION et al. Efficacy and safety of a 121. Kress JP,NOT Pohlman FOR AS, O’Connor SALE MF, OR et al. DISTRIBUTION Daily interruption of paired sedation and ventilator weaning protocol for mechani- sedative infusions in critically ill patients undergoing mechanically ventilated patients in intensive care (Awakening and cal ventilation. N Engl J Med. 2000;342:1471–1477. Breathing Controlled trial): a randomised controlled trial. Lan- 122. Esteban A, Frutos F, Tobin MJ, et al. A comparison of four meth- cet. 2008;371(9607):126–134. ods of weaning patients from mechanical ventilation. N Engl J 101. Strøm T, Martinussen T, Toft P. A protocol of no sedation for Med. 1995;6:345–350. © Jones & Bartlettcritically Learning, ill patients receiving LLC mechanical ventilation: a ran-© Jones123. Brochard& Bartlett L, Rauss Learning, A, Benito S, etLLC al. Comparison of three NOT FOR SALEdomised OR trial.DISTRIBUTION Lancet. 2010;375:475–480. NOT FORmethods SALE of gradual OR withdrawalDISTRIBUTION from ventilatory support during

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weaning from mechanical ventilation. Am J Respir Crit Care on chronic respiratory failure: a prospective, randomized, con- © Jones & BartlettMed. 1994;150:896–903. Learning, LLC © Jonestrolled & Bartlett study. Am JLearning, Respir Crit Care LLCMed. 1999;160:86–92. NOT FOR SALE124. Ely OREW, Baker DISTRIBUTION AM, Dunagan DP, et al. Effect of the duration ofNOT 131. FOR Nava SALE S, Ambrosino OR DISTRIBUTIONN, Clini E, et al. Noninvasive mechanical mechanical ventilation on identifying patients capable of breath- ventilation in the weaning of patients with respiratory failure ing spontaneously. N Engl J Med. 1996;335:1864–1869. due to chronic obstructive pulmonary disease: a randomized, 125. Ely EW, Bennett PA, Bowton DL, et al. Large-scale implemen- controlled trial. Ann Intern Med. 1998;128:721–728. tation of a respiratory therapist-driven protocol for ventilator 132. Esteban A, Frutos-Vivar F, Ferguson ND, et al. Noninvasive weaning. Am J Respir Crit Care Med. 1999;159:439–446. positive-pressure ventilation for respiratory failure after extuba- 126. Robertson TE, Mann© HJ,Jones Hyzy R, & et al.Bartlett Multicenter Learning, implemen- LLC tion. N Engl J Med. 2004;350:2452–2460.© Jones & Bartlett Learning, LLC tation of a consensus-developed,NOT FOR evidence-based, SALE OR spontaneous DISTRIBUTION 133. Keenan SP, Powers C, McCormackNOT DG, FOR Block SALE G. Noninvasive OR DISTRIBUTION breathing trial protocol. Crit Care Med. 2008;36:2753–2762. positive-pressure ventilation for postextubation respiratory dis- 127. Straus C, Louis B, Isabey D, et al. Contribution of the endotra- tress: a randomized controlled trial. JAMA. 2002;287:3238–3244. cheal tube and the upper airway to breathing workload. Am J 134. Marelich GP, Murin S, Battistella F, et al. Protocol weaning Respir Crit Care Med. 1998;157:23–30. of mechanical ventilation in medical and surgical patients by 128. Esteban A, Alia I, Gordo F, et al. Extubation outcome after respiratory care practitioners and nurses: effect on weaning © spontaneousJones & breathing Bartlett trials Learning,with T-tube or pressure-supportLLC time and© incidence Jones of &ventilator-associated Bartlett Learning, pneumonia. LLCChest. ventilation. Am J Respir Crit Care Med. 1997;156:459–465. 2000;118:459–467. 129.NOT Esteban FOR E, Alia SALE I, Tobin MJ, OR et al. DISTRIBUTION Effect of spontaneous breathing 135. Ely EW,NOT Meade FORMO, Haponik SALE EF, etOR al. MechanicalDISTRIBUTION ventilator trial duration on outcome of attempts to discontinue mechanical weaning protocols driven by nonphysician health-care profes- ventilation. Am J Respir Crit Care Med. 1999;159:512–518. sionals: evidence-based clinical practice guidelines. Chest. 130. Girault C, Daudenthun I, Chevron V, et al. Noninvasive ventila- 2001;120(6 suppl):454S–463S. tion as a systematic extubation and weaning technique in acute © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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