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Principles of Mechanical Ventilation

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CHAPTER © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 1NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC PrinciplesNOT FOR SALE OR DISTRIBUTION of MechanicalNOT FOR SALE OR DISTRIBUTION Ventilation © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONDavid W. Chang, EdD,NOT RRT FOR SALE OR DISTRIBUTION © s_maria/Shutterstock © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION OUTLINE OBJECTIVES Introduction © Jones & Bartlett Learning, LLC1. Define and explain the clinical© significanceJones & of Bartlett airflow Learning, LLC Airway Resistance NOT FOR SALE OR DISTRIBUTIONresistance. NOT FOR SALE OR DISTRIBUTION Factors Affecting Airway Resistance 2. Define and explain the clinical significance of static Airway Resistance and Work of Breathing compliance and dynamic compliance. Effects on Ventilation and Oxygenation 3. Describe the clinical application of plateau pressure and Waveform Displays peak inspiratory pressure. Compliance 4. Describe the clinical application of pressure-volume Measurement© Jones of &Compliance Bartlett Learning, LLC (compliance)© Jones slope. & Bartlett Learning, LLC AbnormalNOT LungFOR Compliance SALE OR DISTRIBUTION 5. DescribeNOT the clinical FOR application SALE of ORPIP-Pplat DISTRIBUTION pressure gradient. Plateau Pressure and Peak Inspiratory Pressure 6. Describe the relationship between dead space ventilation and Pressure-Volume Slope rapid shallow breathing pattern. Effects on Ventilation and Oxygenation 7. Define and describe the causes leading to ventilatory Dead Space Ventilation failures. Anatomic Dead Space 8. Define and describe the causes leading to oxygenation © Jones & BartlettAlveolar Dead Learning, Space LLC © Jones failures.& Bartlett Learning, LLC Physiologic Dead Space 9. List the pulmonary and nonpulmonary conditions leading to NOT FOR SALEVentilatory OR Failure DISTRIBUTION NOT FORmechanical SALE ventilation. OR DISTRIBUTION Hypoventilation Ventilation-Perfusion Mismatch KEY TERMS Intrapulmonary Shunting Diffusion Defects airflow resistance plateau pressure Oxygenation Failure © Jones & Bartlett Learning, LLCdead space ventilation ©pressure-volume Jones & Bartlett slope Learning, LLC Hypoxemia and Hypoxia dynamic compliance static compliance Clinical Signs of HypoxiaNOT FOR SALE OR DISTRIBUTIONhypoxemia NOTventilation-perfusion FOR SALE OR DISTRIBUTION Conditions Leading to Mechanical Ventilation hypoxia mismatch Gas Exchange Abnormalities intrapulmonary shunting ventilatory failure Depressed Respiratory Drive oxygenation failure Excessive Ventilatory Workload peak inspiratory pressure Failure of Ventilatory Pump Summary© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC CaseNOT Study FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Bibliography © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 1 © Jones & Bartlett Learning LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION. 9781284202175_CH01_001_012.indd 1 05/12/19 10:43 AM 2 CHAPTER 1 Principles of Mechanical Ventilation © Jones &Introduction Bartlett Learning, LLC © JonesThere & Bartlett are many Learning,conditions that LLC can increase the air- way resistance. Two common diseases with increased Mechanical ventilation is an invasive procedure to pro- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION airway resistance are asthma and COPD (e.g., emphy- vide partial or full support of a patient’s ventilation and sema, chronic bronchitis, and bronchiectasis). Me- oxygenation needs. Indications for mechanical ventila- chanical factors that increase airway resistance include tion include numerous clinical conditions that fail to foreign body aspiration, main stem intubation, and meet these gas exchange requirements. Examples include artificial airways for mechanical ventilation. Infectious abnormal functioning© of Jones the respiratory & Bartlett drive (e.g., Learning, drug LLC © Jones & Bartlett Learning, LLC processes include laryngotracheobronchitis (croup), overdose, postanesthesiaNOT recovery, FOR traumaticSALE OR brain DISTRIBUTION injury), NOT FOR SALE OR DISTRIBUTION epiglottitis, and bronchiolitis. ventilatory pump (e.g., flail chest, diaphragm), airway (e.g., The normal airway resistance (of the natural airways) epiglottitis, status asthmaticus), and lung parenchyma in adults is between 0.5 and 2.5 cm H O/L/sec. The total (e.g., acute respiratory distress syndrome [ARDS], chronic 2 resistance of all airways in the tracheobronchial tree is obstructive pulmonary disease [COPD]). referred to as airways resistance. It is higher in intu- Durations© Jones of & mechanical Bartlett ventilation Learning, range LLC from less © Jones & Bartlett Learning, LLC bated patients due to the small diameter of the ET tube. thanNOT an hour FOR (e.g., SALE postanesthesia OR DISTRIBUTION recovery) to years (e.g., NOT FOR SALE OR DISTRIBUTION Airway resistance varies directly with the length and high spinal cord injury). Locations for use of mechanical inversely with the diameter of the airway or ET tube. ventilation include acute care units, mass casualty situa- A shortened ET tube or tracheostomy tube facilitates tions, long-term care facilities, and at home. This chapter airway management and removal of secretions. It also covers the essential principles of normal and abnormal reduces mechanical dead space and airway resistance. © Jones & respiratoryBartlett physiologyLearning, for LLCspontaneous breathing and © Jones & Bartlett Learning, LLC However, the main determinant of increased airway NOT FOR SALEhow they OR relate DISTRIBUTION to the use of mechanical ventilation. NOT FOR SALE OR DISTRIBUTION resistance is the internal diameter of the ET tube. For this reason, the largest but appropriately sized ET tube Airway Resistance should be used for mechanical ventilation. Once the pa- Airway resistance (Raw) is a mechanical factor affecting tient is intubated, patency of the ET tube must be main- the airflow in the airways.© Jones Airflow & resistance Bartlett has Learning, a simi- LLCtained as secretions inside the© ET Jones tube greatly & Bartlett increase Learning, LLC lar definition, exceptNOT it can FOR be used SALE to describe OR DISTRIBUTIONthe con- the airway resistance. NOT FOR SALE OR DISTRIBUTION dition in the airways or in the lungs. Airway resistance Besides the ET tube, the ventilator circuit and con- is considered the nonelastic airflow resistance, because densation collected in it also contribute to the airflow the airway diameter changes minimally during respira- resistance. Pressure support ventilation (PSV) is often tion. The elastic recoil of the lungs contributes to the used to compensate for airflow resistance and to aug- elastic© Jones resistance & toBartlett gas flow. Learning, The total airflow LLC resistance ment spontaneous© Jones breathing & Bartlett efforts. Learning, LLC is theNOT sum FOR of nonelastic SALE and OR elastic DISTRIBUTION resistance. The de- NOT FOR SALE OR DISTRIBUTION gree of airway resistance is primarily determined by the Airway Resistance and Work of Breathing length, internal diameter, and patency of the airway. The Airway resistance (Raw) is calculated by pressure gradi- patency of the airway may be reduced in conditions of ent (ΔP)/flow: retained secretions, bronchospasm (nonelastic airflow Pressure gradient (P∆ ) © Jones & resistance),Bartlett Learning,or compression LLC of the lung parenchyma (i.e.,© Jones & BartlettRaw = Learning, LLC NOT FOR SALEelastic airflow OR DISTRIBUTION resistance). For mechanically ventilated NOT FOR SALE OR DISTRIBUTIONFlow patients, the endotracheal (ET) tube and ventilator cir- The pressure gradient (ΔP) in the equation reflects the cuit impose additional airflow resistance to the airways. work of breathing. Since Raw is directly related to ΔP, an Factors Affecting Airway Resistance increase in airway resistance will increase the work of breathing. If the work of breathing remains unchanged Airflow obstruction ©causes Jones different & Bartlett degrees Learning,of resis- LLCin the presence of increased airway© Jones resistance, & Bartlett the flow Learning, LLC tance in the airways.NOT It is increased FOR SALE when the OR patency DISTRIBUTION (or volume) will decrease. In NOTessence, FOR an increase SALE in OR DISTRIBUTION or diameter of the airways is reduced. Airflow obstruc- airway resistance will lead to an increase in work of tion may be caused by changes inside the airway (e.g., breathing or a decrease in flow (or volume). In a clini- retained secretions), in the wall of the airway (e.g., neo- cal setting, relief of airflow obstruction is an effective plasm of the bronchial muscle structure), or outside the way to improve ventilation and to reduce the work of airway© Jones (e.g., tumors & Bartlett surrounding Learning, and compressing LLC the breathing. © Jones & Bartlett Learning, LLC airway).NOT These FOR conditionsSALE OR reduce DISTRIBUTION the internal diameter NOT FOR SALE OR DISTRIBUTION of the airway and increase the airway resistance. The Effects on Ventilation and Oxygenation simplified Poiseuille’s law shows that when the radius An increase in airway resistance hinders ventilation of a circle is reduced by 50%, the driving pressure (∆P) and oxygenation. If an abnormally high airway resis- must increase by a factor of 16-fold
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