2010 mechanical ventilation

CHAPTER © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 22 Mechanical Ventilation © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Dean R Hess Neil MacIntyre © R Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION OUTLINE proportional assist patient–ventilator ventilation (PAV) asynchrony The Equation of Motion spontaneous breathing peak inspiratory Indications for Mechanical Ventilation trial (SBT) pressure (PIP) Complications of Mechanical Ventilation synchronized permissive hypercapnia © Jones & Ventilator BartlettSettings Learning, LLC © Jones & Bartlett Learning, LLC intermittent plateau pressure NOT FOR SALE ORtheDISTRIBUTION NOT FOR SALE OR DISTRIBUTION mandatory Monitoring Mechanically Ventilated Patient ventilation (SIMV) positive end-expiratory Choosing Ventilator Settings for Different Forms of transpulmonary pressure pressure (PEEP) Respiratory Failure ventilator-induced lung pressure control Ventilatory Support Involves Trade-Offs injury (VILI) ventilation (PCV) Liberation from Mechanical Ventilation control pressure support © Jones & Bartlett Learning, LLC ©volume Jones & Bartlett Learning, LLC ventilation ventilation (PSV) NOT FOR (VCV) SALE OR DISTRIBUTION OBJECTIVES NOT FOR SALE OR DISTRIBUTION weaning parameters pressure triggering List the indications for and complications of mechanical ventilation Discuss issues related to ventilator-associated injury © lung Jones & Bartlett Learning, LLC Select appropriate ventilator settings NOT FOR SALE OR DISTRIBUTION List parameters that should be monitored during mechanical ventilation Discuss issues related to liberation from mechanical ventilation INTRODUCTION Mechanical ventilation is an important life support technology © that is an integral component of critical Jones & Bartlett Learning, LLC care Mechanical ventilation can be applied as negaNOT FOR SALE OR DISTRIBUTION tive pressure to the outside of the thorax (e.g., the iron lung) or, most often, as positive pressure to the airway The desired effect of positive pressure ventilation is to maintain adequate levels of PaO2 and PaCO2 while also unloadingLearning, the inspiratory muscles Mechani© Jones & KEY Bartlett Learning, LLC © Jones & Bartlett LLC TERMS cal ventilation is a life-sustaining technology, but recNOT FOR SALE DISTRIBUTION NOT FOR SALE OR DISTRIBUTION high-frequency adaptiveOR pressure ognition is growing that when used incorrectly, it can oscillatory ventilation control increase morbidity and mortality Positive pressure (HFOV) adaptive support ventilation is provided in intensive care units (ICUs), intermittent mandatory ventilation (ASV) subacute facilities, long-term care facilities, and the ventilation airway pressure release home Positive pressure ventilation can be invasive Learning, LLC & Bartlett ventilator Learning, LLC © Jones & Bartlett lung-protective ventilation (APRV) © Jones (i.e., with an endotracheal tube or tracheostomy tube) NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION strategy auto-PEEP or noninvasive (e.g., with a face mask) This chapter mean airway pressure compressible volume addresses invasive positive pressure ventilation as – (Paw) continuous mandatory it is applied in adults with acute respiratory failure neurally adjusted ventilation (CMV) Modern ventilators used in the intensive care unit are ventilatory assist continuous positive microprocessor controlled and available from several © Jones & Bartlett LLC © Jones & Bartlett Learning, LLC (NAVA) airway pressure (CPAP) Learning, manufacturers ( Figure 22–1 and Figure 22–2) NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION flow triggering oxygen toxicity © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 462 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Mechanical Ventilation © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC SALE OR DISTRIBUTION FIGURE Examples of mechanical ventilators commonly used in critical care in theNOT United States NOT22–1 FOR SALE OR DISTRIBUTION FOR © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 463 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 464 CHAPTER 22 Mechanical Ventilation Equation of Motion © Jones &The Bartlett Learning, LLC Positive pressure, when applied NOT FOR SALE OR DISTRIBUTIONat the air- Expiratory valve © Jones &(PEEP) Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Atmosphere way opening, interacts with respiratory system (lung and chest wall) compliance, airways resistance, respiratory system inertance, and tissue resistance to produce gas flow into the lung andBartlett tissue Electrical ©Inertance Jones & Learning, LLCMicroprocessor (mode and breath delivery) resistance are smallNOT and their effects areORpower FOR SALE DISTRIBUTION usually ignored The interactions of airway pressure (Paw), respiratory muscle pressure (Pmus), flow, and volume with respiFilter Air ratory system mechanics can be expressed as the equation& of Bartlett motion: Learning, LLC © Jones © Jones & O2 FOR SALE OR DISTRIBUTION PawNOT ϩ Pmus ϭ (Flow ϫ Resistance) ϩ (Volume/Compliance) InspiratoryNOT valve(s) FOR (flow, volume, pressure, FIO2) Filter © Jones Monitors & Bartlett Learning, LLC Patient and alarms NOT FOR SALE OR DISTRIBUTION Bartlett Learning, LLC SALEHumidifier OR DISTRIBUTION FIGURE 22–2 Modern ventilators are electronically and pneumatically controlled The For spontaneous breathing, Paw ϭ 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 phase The expiratory valve controls positive end-expiratory pressure (PEEP) © Jones & isBartlett LLCmuscles For expiratory © Jones & Bartlett Learning, LLC provided Learning, by the respiratory The inspiratory and expiratory valves are controlled by the microprocessor Sensors full ventilatory support, Pmus ϭ and all NOT FOR SALE OR DISTRIBUTION NOTand FOR SALE OR DISTRIBUTION measure pressure flow, which are displayed 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 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ventilation BOX 22–1 For full ventilatory support, the ventilator controls NOT FOR SALE OR DISTRIBUTION 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 Apnea if flow and volume are controlled (volume-targeted Acute ventilatory failure (e.g., © JonesThe & Bartlett © Jones & Bartlett Learning, LLC ventilation) equation ofLearning, motion alsoLLC predicts that rising Paco with acidosis, flow and volume will vary for a given resistance and NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION respiratory muscle dysfunccompliance if Paw is controlled (pressure-targeted tion, excessive ventilatory ventilation) load, altered central ventilaAn important point to remember in considering the tory drive) equation of motion is that in the setting of high minute Impending ventilatory LLC failure ventilation, long inspiratory-to-expiratory time ratios, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, Severe oxygenation deficit and prolonged expiratory time constants (e.g., as seen in NOT FOR SALE OR DISTRIBUTION NOT 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 from drug overdose or from©anesthesia with delivery © Jones & Bartlett Learning, LLC Jones &involved Bartlett Learning, LLC major surgery is an indication that does not involve NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION primary respiratory system failure In short, mechanical Indications for 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 22–1 ) Goals of mechanical ventilation are shown that the patient’s life is threatened © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC in NOT Box 22–2 Although these conditions are useful in FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION the determination of whether mechanical ventilation Complications of Mechanical is needed, clinical judgment is as important as strict Ventilation adherence to absolute guidelines One indication for Mechanical ventilation is not a benign therapy, and mechanical ventilation is imminent acute respiratory it can & have major effects on theLLC body’s homeostasis failure; in such cases, initiating mechanical ventilation © Jones & Bartlett Learning, LLC © Jones Bartlett Learning, ( Box 22–3 ) In addition to the serious may prevent overt respiratory failure and respiratory NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONcomplications reviewed here associated with positive pressure applied arrest On the other hand, depression of respiratory drive © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Complications of Mechanical Ventilation to the lungs,3 intubated mechanically ventilated patients 465 bleeding5 and often are given antacids, proton pump © Jones & Bartlett Learning, LLC to prevent this © Jones &also Bartlett Learning, LLC associated with the use are at risk for complications inhibitors, or histamine (H2) blockers NOT FOR SALE OR DISTRIBUTION NOT FOR SALE ORairways, DISTRIBUTION of artificial the most serious being accidental complication The nutritional needs of mechanically disconnection and the development of pneumonia from compromised natural airway defenses Mechanically ventilated patients are also at risk for gastrointestinal ventilated patients play an important role in preventing or promoting complications.6 Undernourished patients are at risk for respiratory muscle weakness and pneumonia An excessive caloric intake, on the other hand, may © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC increase carbon dioxide (CO2) production, which can NOT FOR SALE OR DISTRIBUTION NOT FOR requirements SALE OR DISTRIBUTION markedly increase the patient’s ventilatory BOX 22–2 Sleep deprivation in mechanically ventilated patients has recently become recognized.7 Goals of Mechanical Ventilation Provide adequate oxygenation Ventilator-Induced Injury Learning, LLC Provide adequate alveolar © Jones & Bartlett Learning, LLC © Jones Lung & Bartlett The application positive pressure the airways can ventilation NOT FOR SALE OR DISTRIBUTION NOTofFOR SALE ORtoDISTRIBUTION create lung injury under a variety of circumstances Avoid alveolar overdistension Pulmonary barotrauma (e.g., subcutaneous emphyMaintain alveolar recruitment sema, pneumothorax, pneumomediastinum) is one of Promote patient–ventilator the most serious complications of excessive pressure synchrony and volume deliveryLearning, to the lung and is a consequence of auto-PEEP © Jones & Bartlett Avoid Learning, LLC © Jones & Bartlett LLC alveolar overdistention Use the lowest possible Fio NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION RESPIRATORY RECAP to the point of rupture When choosing appropriate goals ( Figure 22–3 ) Howof mechanical ventilation for Types of Ventilator-Induced Lung Injury ever, even when the lung an individual patient, consider » Volutrauma is not distended to the the risk of ventilator-induced » Atelectrauma point of rupture, exceslung injury © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC » Biotrauma sive transpulmonar y NOT FOR SALE OR DISTRIBUTION NOT FOR toxicity SALE OR DISTRIBUTION » Oxygen stretching pressures 22–3 © Jones & BOX Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Complications of Mechanical Ventilation Airway Complications Cardiovascular Complications Laryngeal edema Reduced venous return Tracheal mucosal trauma cardiac output © Jones & Bartlett Learning, LLC © JonesReduced & Bartlett Learning, LLC Contamination of the lower respiratory tract Hypotension NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Loss of humidifying function of the upper Gastrointestinal and Nutritional airway Complications Mechanical Complications Gastrointestinal bleeding Accidental disconnection Malnutrition © Jones Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Leaks in the ventilator&circuit Renal Complications NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Loss of electrical power Reduced urine output Loss of gas pressure 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 © Jones & Bartlett Learning, LLC Sleep deprivation Oxygen toxicity NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Increased intracranial pressure Atelectasis Critical illness weakness Nosocomial pneumonia Inflammation Acid–Base Complications Auto-PEEP Respiratory acidosis Asynchrony alkalosis © Jones & Bartlett Learning, LLC © JonesRespiratory & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 466 CHAPTER 22 Mechanical Ventilation beyond the normal maximum (i.e., 30 to 35 cm H O) Importantly, this approach may require acceptance of © Jones & Bartlett Learning, © Jones &can Bartlett LLC produceLearning, a parenchymal lung injury not associated less than normal values for pH andLLC Pao2 in exchange for NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION with extra-alveolar air (ventilator-induced lung injury lower (and safer) distending 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, LLC chest strapping) prevents lung injury even in the face of alveolus may exceed 100 cm H2O during this process.16 NOT FOR SALE OR DISTRIBUTION NOT SALE very high applied airway pressures This injury is reduced with the useFOR of smaller tidalOR vol-DISTRIBUTION Clinical trials have confirmed these animal observaumes and may be ameliorated by optimal lung recruittions 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 H2O are associated with lung however, can be a two-edged sword If an increase in © Jones & Bartlett 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, NOT FOR SALE OR DISTRIBUTION NOT(distribution FOR SALE OR DISTRIBUTION simply the result of excessive end-inspiratory alveothen the stress of pressure) 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 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) may contribute to VILI.9,10,13 This provides the rationale on the lungs is increased.17 Other ventilatory pattern © Jones & for Bartlett Learning, LLC © Jones & Bartlett Learning, LLC using lung-protective ventilator strategies that limit factors may also be involved in the development of VILI NOT FOR SALE OR DISTRIBUTION NOTThese FORinclude SALEfrequency OR DISTRIBUTION tidal volume and end-inspiratory distending pressures of stretch18 and the acceleration 19 or velocity of stretch Vascular pressure elevations may also contribute to VILI.20 VILI is manifest pathologically as diffuse alveolar damage,7,8,15 and it increases inflammatory cytokines © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC in the lungs (biotrauma).21–24 VILI is also associated NOT FOR SALE OR DISTRIBUTION NOT SALE OR DISTRIBUTION with systemic cytokine release andFOR bacterial transloca24 tion that are implicated in the systemic inflammatory response with multiorgan dysfunction that increases mortality The way in which the lungs are ventilated may therefore play a role in systemic inflammation © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC (Figure 22–4) NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Oxygen Toxicity Oxygen concentrations approaching 100% are known to cause oxidant injuries in airways and lung parenchyma.25 Much & of the data supporting the concept © Jones Bartlett Learning, LLC of oxygen toxicity, however, have come from animals that often have quite NOT FOR SALE OR DISTRIBUTION different tolerances to oxygen than humans It is unclear what the safe oxygen concentration or duration of exposure is in sick humans, MODS such as those with acute lung injury (ALI) or acute respiratory distress syn© Injury Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Biochemical drome (ARDS) Many authorities have Cytokines, complement, NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Distal Organs argued that a fraction of inspired oxygen prostanoids, leukotrienes, – Tissue injury secondary to Bacteria (Fio2) less than 0.4 is safe for prolonged reactive oxygen species, inflammatory mediators cells proteases periods of time and that a Fio2 greater – Impaired oxygen delivery – Bacteremia than 0.80 should be avoided However, Mechanical VILI & may be moreLearning, important cliniventilation © Jones & Bartlett Learning, LLC © Jones Bartlett LLC Neutrophils cally than oxygen toxicity In one large Biophysical NOT FOR SALE Injury OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION – Alveolar–capillary permeability – Shear study (ARDSnet), survival was greater – Cardiac output – Overdistention in patients with ALI/ARDS who were – Organ perfusion – Cyclic stretch ventilated with a lower tidal volume, – Intrathoracic pressure presumably avoiding significant VILI, FIGURE 22–4 Mechanical ventilation can result in biochemical and biophysical injury to despite the fact LLC that the required Fio2 © Jones & the Bartlett Learning, LLC organ failure MODS, multiple © Jones & Bartlett Learning, lungs, which may result in multisystem organ dysfunction was higher in the group receiving the syndrome.OR Adapted from Slutsky AS, Trembly L Multiple system organ failure: is mechanical NOT FOR SALE DISTRIBUTION NOT FOR SALE OR DISTRIBUTION lower tidal volumes ventilation a contributing factor? Am J Respir Crit Care Med 1998;157:1721–1725 FIGURE 22–3 Computed tomography scan of the thorax of a mechanically ventilated patient with severe barotrauma © Jones & Bartlett Learning, LLC pneumomediastinum, Note the presence of pneumothorax, and subcutaneous emphysema NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Ventilator Settings Ventilator-Associated Pneumonia 467 As intrathoracic pressure increases with positive © Jones & Bartlett LLC filling decreases © Jones & Bartlett Learning, LLC pressure ventilation,Learning, right ventricular The natural laryngeal mechanism that protects the lower NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION and cardiac output decreases This is the rationale for respiratory tract from aspiration is compromised by an using volume repletion to maintain cardiac output in endotracheal tube This permits oropharyngeal debris the setting of high intrathoracic pressure The effect of to leak into the airways The endotracheal tube also reduced cardiac filling on cardiac output may be parimpairs the cough reflex and serves as a potential portal tially counteracted by better left ventricular function due for pathogens to enter lungs.& The underlying disease LLC © the Jones Bartlett Learning, © Jones & Bartlett Learning, LLC to elevated intrathoracic pressures, which reduce left process makes the lungs prone to infection Finally, heavy 33 NOT FOR SALE OR DISTRIBUTION NOTwith FOR OR DISTRIBUTION ventricular afterload In patients leftSALE heart failure, antibiotic use in the ICU and the presence of very sick the reduced cardiac fillpatients in close proximity to each other are risk factors RESPIRATORY RECAP ing and reduced left venfor antibiotic-resistant infection tricular afterload effects Indications for and Preventing ventilator-associated pneumonia (VAP) Complications of Mechanical of elevated intrathoracic is important it is associated with morbidity © Jonesbecause & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Ventilation pressure may actually and mortality.26 VAP prevention has become an impor» Mechanical ventilation NOT FOR SALE OR DISTRIBUTION 26–29 improve cardiac NOT FOR SALE OR DISTRIBUTION functant priority in the mechanically ventilated patient is indicated to support tion such that intrathooxygenation and ventilation Hand washing, elevating the head of the bed, and careracic pressure removal of patients with acute fully choosing antibiotic regimens can have important respiratory failure may produce left venpreventive effects Circuit changes only when vis» A number of complications tricular failure if positive 30 contaminated appearLLC to be helpful Endotracheal © Jones & ibly Bartlett Learning, © Jones & Bartlett Learning, LLC are possible with mechanical pressure ventilation is tubes that continuous drainage of subglottic ventilation, and efforts must 34 NOT FOR SALE ORprovide DISTRIBUTION NOTremoved FOR SALE OR DISTRIBUTION secretions, endotracheal tubes with specialized cuff be made to minimize these Intrathoracic presconditions designs, and endotracheal tubes made with antimicrosure can also influence bial materials are other ways of reducing lung contamidistribution of perfusion, as described by the West model nation with oropharyngeal material However, these of pulmonary perfusion In the supine human lung, tubes are more expensive and their cost-effectiveness is © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC blood flow is greatest in zone As intra-alveolar pres31 controversial NOT FOR SALE OR DISTRIBUTION FOR OR DISTRIBUTION sure rises, there is an increaseNOT in zone andSALE zone (dead и) space) regions, creating high ventilation-perfusion (Vи/Q Auto-PEEP units Dyspnea, anxiety, and discomfort associated with inadequate ventilatory support can lead to stress-related catecholamine release, with increases in myocardial © Jones & Bartlett Learning, LLC oxygen demands and risk of dysrhythmias.34 In addition, NOTvessel FORoxygen SALE OR DISTRIBUTION coronary blood delivery can be compromised by inadequate gas exchange from the lung injury coupled with low mixed venous Po2 due to high oxygen consumption demands by the inspiratory muscles Auto-PEEP (also known as intrinsic PEEP or air trapping) is the result of the lungsLearning, not returning to the base© Jones & Bartlett LLC line proximal airway pressure at end-exhalation The NOT FOR SALE OR DISTRIBUTION determinants of auto-PEEP are high minute volume, long inspiratory-to-expiratory time relationships, and long expiratory time constants (i.e., obstructed airways and high-compliance alveolar units) Auto-PEEP raises intrathoracic pressures,LLC which can affect gas delivery, © Jones & all Bartlett Learning, © Jones & Bartlett Learning, LLC hemodynamics, end-inspiratory distention (and thus NOT FOR SALE OR DISTRIBUTION NOTVentilator FOR SALE Settings OR DISTRIBUTION VILI), and patient breath triggering Although someVolume Control Versus Pressure Control times desired in long inspiratory time ventilatory strategies, auto-PEEP is generally to be avoided because it is With volume control ventilation (VCV) , the ventiladifficult to recognize and to predict its effects tor controls the inspiratory flow (Figure 22–5) The tidal © Jones & Bartlett Learning, LLC volume is deter© Jones & Bartlett Learning, LLC mined by the flow and RESPIRATORY NOT FOR SALE OR DISTRIBUTION NOT FOR SALERECAP OR DISTRIBUTION Hemodynamic Effects of Positive the inspiratory time In Volume Control Versus Pressure Ventilation practice, however, the Pressure Control Ventilation flow and tidal volume Because positive pressure ventilation increases intratho» Volume control: Ventilation are set on the ventilaracic pressure, it can reduce venous return, which may remains constant with in respiratory tor With VCV the tidal result in decreased cardiac output and a drop in arterial © Jones & Bartlett Learning, LLC © Jones & Bartlettchanges Learning, LLC mechanics, but airway volume is delivere d blood pressure Fluid administration and drug therapy NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION and plateau pressures can regardless of resistance (such as with vasopressors and inotropes) may be necfluctuate or compliance, and the essary to maintain cardiac output, blood pressure, and » Pressure control: Ventilation peak airway pressure urine output under these circumstances Mechanical fluctuates with changes in varies (Box 22–4) VCV ventilation also can cause an increase in plasma antidirespiratory mechanics, but pressure is limited to the should be used whenuretic hormone (ADH) and a decrease in atrial natri© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC peak pressure set on the ever a constant tidal voluretic peptide (ANP), which may reduce urine output NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ventilator 32 ume is important in the and promote fluid retention © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 468 CHAPTER 22 Mechanical Ventilation maintenance of a desired Paco , such as with an acute ramp A descending ramp flow pattern produces a longer overdistention in the lungs Also, because the inspiratory flow is fixed, VCV can cause patient–ventilator asynchrony, particularly if the inspiratory flow is set too low With VCV, the set flow can be constant or a descending (Figure 22–6), the airway pressure is set and remains constant despite changes in resistance and compliance Box 22–5 lists factors that affect the tidal volume with PCV The principal advantage of PCV is that it prevents © Jones & Bartlett Learning, LLC © Jones &head Bartlett injury.Learning, The principalLLC disadvantage of VCV is that inspiratory time unless the peak flow is increased NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION it can produce a high peak alveolar pressure and areas of With p r e s s u r e c o n t r o l v e n t i l a t i o n ( P C V ) Flow (L/min) © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 40 © Jones & Bartlett Learning, LLC –40 NOT FOR SALE OR DISTRIBUTION –80 Pressure (cm H2O) © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 50 © Jones & Bartlett Learning, 40 LLC 30 NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 10 12 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 20 10 10 12 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 600 Volume (mL) 400 200 Flow (L/min) © Jones & Bartlett Learning, LLC (A) NOT FOR SALE OR DISTRIBUTION Time (s) 14 Learning, LLC © 10 Jones &12Bartlett NOT FOR SALE OR DISTRIBUTION 40 –40 © Jones & Bartlett Learning, LLC –80 NOT FOR SALE OR DISTRIBUTION Pressure (cm H2O) 14 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 800 Volume (mL) 14 © Jones & Bartlett Learning, LLC NOT FOR SALE 10 OR DISTRIBUTION 12 14 50 40 30Jones & Bartlett Learning, LLC © 20 NOT FOR SALE OR DISTRIBUTION 10 800 © Jones & Bartlett Learning, LLC 600 NOT FOR SALE OR DISTRIBUTION 400 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 10 12 14 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 200 10 12 Time (s) 14 (B) © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC FIGURE 22–5 (A) Constant-flow (square wave) NOT volume control Descending ramp-flow NOT FOR SALE OR DISTRIBUTION FORventilation SALE (B) OR DISTRIBUTION volume control ventilation © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Ventilator Settings localized alveolar overdistention with changes in resis- improve patient–ventilator synchrony.35,36 The choice Because the flow can vary with PCV, this mode may disadvantages (Table 22–1).37 469 © Jones & Bartlett Learning, LLC by clinician or © Jones &tance Bartlett Learning,the LLC and compliance; peak alveolar pressure canof VCV or PCV often is determined NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION not be greater than the pressure set on the ventilator institutional bias, and both modes have advantages and © Jones & Bartlett Learning, LLC BOX 22–4 NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC BOX 22–5 NOT FOR SALE OR DISTRIBUTION Factors That Affect Tidal Volume (VT) Factors That Affect Peak with Pressure Control Ventilation Inspiratory Pressure (PIP) with Driving pressure: A higher driving presVolume Control Ventilation sure (difference between peak inspiPeak&inspiratory setting: A LLC © Jones Bartlettflow Learning, © ratory Jones & Bartlett Learning, LLC pressure and PEEP) increases higher flowOR setting increases NOT FOR SALE DISTRIBUTION NOT FOR SALE OR DISTRIBUTION the Vt 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 inspiraflow tory time increases the Vt if inspiend-expiratory © Jones & BartlettPositive Learning, 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 not affect the Vt Auto-PEEP: Auto-PEEP increases Compliance: Decreased compliance the PIP decreases the Vt Tidal volume (V): An increase in Resistance: Increased resistance Vt results in a higher PIP © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC decreases the Vt; after flow decreases Resistance: Greater airways resisNOT FOR SALE OR DISTRIBUTION NOT to zero, resistance no FOR longer SALE affects OR DISTRIBUTION tance results in a higher PIP the delivered Vt Compliance: Decreased compliPatient effort: Greater inspiratory effort ance results in a higher PIP by the patient increases the Vt Flow (L/min) © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 40 © Jones & Bartlett Learning, –40 LLC NOT FOR SALE OR DISTRIBUTION –80 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Pressure (cm H2O) 10 12 14 50 ©40Jones & Bartlett Learning, LLC 30 NOT FOR SALE OR DISTRIBUTION 20 10 © Jones & Bartlett Learning, LLC 800 NOT FOR SALE OR DISTRIBUTION 600 Volume (mL) © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 10 12 14 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 400 200 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION FIGURE 22–6 Pressure control ventilation 10 Learning, 12 14 ©6 Jones 8& Bartlett LLC Time (s) NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION CHAPTER 22 470 Mechanical Ventilation Pressure support ventilation (PSV) (Figure 22–9) is Ventilator Mode © Jones & Bartlett Learning, © Jones & Bartlett Learning, LLC a spontaneous breathing mode in LLC which patient effort is Options for breath delivery are referred to as modes NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION augmented by a clinician-determined level of pressure 38–41 of ventilation Traditional modes include continu- during inspiration.42 Although the clinician sets the level ous mandatory ventilaof pressure support, the patient sets the respiratory rate, tion (CMV), also called RESPIRATORY RECAP inspiratory flow, and inspiratory time The Vt is deterassist/control (A/C), Ventilator Modes mined by the level of pressure support, the amount of intermit- LLC & Bartlett Learning, © Jones & Bartlett Learning, LLC » Continuous mandatory© Jones synchronized patient effort, and the resistance and compliance of the tent mandator y venventilation (CMV) NOT FOR SALE OR DISTRIBUTION patient’s respiratory system NOT FOR SALE OR DISTRIBUTION tilation (SIMV ), and » Synchronized intermittent mandatory ventilation (SIMV) pressure support venti» Pressure support ventilation lation (PSV) The choice TABLE 22–1 Advantages and Disadvantages of Volume (PSV) of mode often is based Control and Pressure Control Ventilation » Continuous positive airway on institutional policy © Jones © Jones & Bartlett Learning, LLC pressure (CPAP) & Bartlett Learning, LLC Type Advantages Disadvantages or the clinician’s bias » Adaptive control OR DISTRIBUTION NOTpressure FOR SALE NOT FOR SALE OR DISTRIBUTION No one mode is clearly (APC) Volume Constant tidal Increased plateau superior; each has its control volume (VT) pressure (Pplat) » Adaptive support ventilation ventilation with changes in with decreasing (ASV) advantages and disadresistance and compliance (alveolar » Airway pressure release vantages (Table 22–2) ■ compliance overdistention) clinicians asynchrony © Jones »& ventilation Bartlett(APRV) Learning, LLC Continuous manda© Jones & Bartlett LLC Type ofLearning, ventilation Fixed inspiratory Tube compensation (TC) tory ventilation (CMV) familiar to most flow may cause NOT FOR» SALE ORassist DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Proportional ventilation (or assist/control ven- » » (PAV) tilation) delivers a set Neurally adjusted ventilatory volume or pressure and assist (NAVA) a minimum respiratory High-frequency oscillatory ventilation (HFOV) ) The (Figure 22–7 © Jones rate & Bartlett Learning, Pressure control ventilation Reduced risk of Changes in VT with overdistention changes in resistance with changes in and compliance compliance © Jones Less familiar type of & Bartlett Learning, LLC Variable flow ventilation for most NOT FOR SALE OR DISTRIBUTION improves clinicians synchrony in some patients LLC Pressure (cm H2O) Flow (L/min) patient canOR trigger addiNOT FOR SALE DISTRIBUTION tional breaths above the minimum rate, but the set volume or pressure remains constant When mechanical ventilation is begun, it often is best to use CMV (assist/control) to produce nearly complete respiratory rest&(i.e., full ventila©muscle Jones Bartlett Learning, © Jones & Bartlett Learning, LLC 60 LLC tory support) Regardless of the 40 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 20 mode used, the goal is to strike a balance between excessive –20 respiratory muscle rest, which –40 promotes atrophy, and exces–60 10 12 14 respiratory muscleLLC activ© Jones & sive Bartlett Learning, © Jones & Bartlett Learning, LLC ity, which promotes fatigue—or, NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 24 put more simply, to avoid the 20 extremes of too much rest and 16 too much exercise Patient-triggered Ventilator-triggered 12 breath Continuous positive airway pressure (CPAP) is©a Jones sponta-& Bartlett Learning, LLC neous breathing mode ( Fig2 NOT FOR SALE OR DISTRIBUTION ure  22–8) The airway pressure breath © Jones & Bartlett Learning, LLC 10 FOR SALE 12 14 DISTRIBUTION NOT OR Volume (mL) is usually but not necessarily 600 greater than atmospheric pres500 sure CPAP is commonly used as 400 300 a means of maintaining alveolar © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 200 recruitment in mild to moderNOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 100 ate forms of pulmonary edema and parenchymal lung injury 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 patienttriggered breaths extubation & taneously Bartlettbefore Learning, LLC © Jones & Bartlett Learning, LLC © Jones NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Ventilator Settings Pressure support ventilation is a frequently used 471 cycle to the expiratory phase without the need for active © Jones & Bartlett Learning, LLC © Jones &mode Bartlett Learning, LLC However, because it is of mechanical ventilation exhalation NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION patient triggered, PSV is not an appropriate mode for The flow at which the ventilator cycles to the expirapatients who 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 mode of ventilation, it can be Several studies have reported asynchrony with PSV in © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC quite complex (Figure 22–10) First, the ventilator must individuals with airflow obstruction, such as chronic 43,44 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION recognize the patient’s inspiratory effort, which depends obstructive pulmonary disease (COPD) With airflow 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 presis too high can produce a pressure overshoot, and a flow sure cycle the breath The problem increases with higher © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC that is too low can result in patient flow starvation and levels of PSV and with higher levels of airflow obstrucNOT FOR SALE OR DISTRIBUTION NOTventilators, FOR SALE DISTRIBUTION asynchrony Third, the ventilator must appropriately tion On newer the OR termination flow can ■ TABLE 22–2 Advantages and Disadvantages of Common Modes of Mechanical Ventilation © Jones & Bartlett Learning, LLC Mode of Ventilation NOT FOR SALE OR DISTRIBUTION Continuous mandatory ventilation (CMV) © Jones & Bartlett Learning, LLC Disadvantages NOT FOR SALE OR DISTRIBUTION Advantages Guaranteed volume (or pressure) with each breath Low patient workload if sensitivity and inspiratory flow set correctly High mean airway pressure Respiratory alkalosis and auto-PEEP if patient triggers at rapid rate Respiratory muscle atrophy possible ©mandatory Jones &Lower Bartlett Learning, Synchronized intermittent mean airway pressure LLC ventilation (SIMV) NOT FOR SALE Prevents respiratory muscle atrophy OR DISTRIBUTION Asynchrony if rate © set Jones too low & Bartlett Learning, LLC High work of breathing withFOR older ventilators NOT SALE OR DISTRIBUTION Pressure support ventilation (PSV) Requires spontaneous respiratory effort Fatigue and tachypnea with PSV too low Activation of expiratory muscles with PSV too high Variable flow may improve synchrony in some patients Overcomes tube resistance Prevents respiratory muscle atrophy © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Ventilator maintains tidal volume with changes Does not precisely control tidal volume NOT FOR SALE OR DISTRIBUTION NOT FOR SALE DISTRIBUTION in respiratory system mechanics Support is taken away if OR the patient’s tidal volume Adaptive pressure control Variable flow may improve synchrony in some patients Adaptive support ventilation (ASV) consistently exceeds target Ventilator adapts settings to patient’s physiology May not precisely control tidal volume May improve ventilation to dependent lung zones May improve oxygenation in patients with ALI or ARDS Phigh–Plow difference May be large transpulmonary pressure swings during spontaneous breathing © 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 OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION (APRV) during the ventilator cycle May result in large tidal volumes, depending on © Jones &Overcomes Bartlettresistance Learning, LLC through artificial airway NOT FOR SALE OR DISTRIBUTION Tube compensation (TC) Proportional assist ventilation (PAV) Pressure applied to the airway is determined by respiratory drive and respiratory mechanics © Jones & Bartlett Learning, LLC DISTRIBUTION Effect is usually small and may not affect patient NOT FOR SALE OR outcomes Not useful with weak drive or weak respiratory muscles Clinician has little control over tidal volume or respiratory rate © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Pressure applied to the airway is determined NOT Requires insertion of special tube to DISTRIBUTION FOR SALE ORgastric DISTRIBUTION Neurally NOTadjusted FOR ventilatory SALE assist OR (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 respiratory distress syndrome; EMG, & Bartlett Learning, LLCelectromyelogram © Jones & Bartlett Learning, LLC © Jones NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 486 CHAPTER 22 Mechanical Ventilation Changes in esophageal pressure, relative to changes in positive (i.e., PEEP is greater than esophageal pressure) © Jones Bartlett Learning, LLC © Jones &alveolar Bartlett Learning, pressure, can beLLC used to calculate transpul(Figure&22–33 ) This is most likely with a decrease in NOT FOR SALE OR DISTRIBUTION NOT FOR SALE DISTRIBUTION monary OR pressure (lung stress) This may allow more chest wall compliance, 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, transthis 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 H2O especially in supine critically ill patients, make it very diffi© Jones & 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 86 NOT FOR SALE OR DISTRIBUTION NOT FOR SALEbladder OR DISTRIBUTION to allow more precise setting of PEEP If pleural pressure patients with abdominal compartment syndrome, is high relative to alveolar pressure (i.e., PEEP), then there pressure may be useful to assess intra-abdominal presmay 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 60 FOR SALE OR DISTRIBUTION NOT © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Flow (L/min) 40 20 –20 –40 Bartlett –60 Paw (cm H2O) Pes (cm H2O) © Jones & Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 32 Esophageal pressure 16 Ccw = VT/⌬ ⌬Pes = 350 mL/5 cm H2O = 70 mL/cm H2O Airway pressure 24 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Volume (mL) 400 300 200 © Jones & Bartlett Learning, LLC 100 NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Time (s) FIGURE 22–32 Calculation of chest wall compliance The esophageal pressure increases by cm H2O with a tidal volume of 350 mL in a passively ventilated patient © Jones & Bartlett Learning, LLC 60 NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Flow (L/min) 40 20 –20 –40 Paw (cm H2O) Pes (cm H2O) 40 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 10 12 14 30 © Jones & Bartlett Learning, LLC 20 NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 10 10 Time (s) 12 14 © Jones & Bartlett Learning, LLC © Jones & 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 FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION positive because PEEP is greater than the esophageal pressure © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Monitoring the Mechanically Ventilated Patient After bronchodilator © Jones & Bartlett Learning, LLC 60 NOT FOR SALE OR DISTRIBUTION 487 are lowest) to account for the respiratory varia- © Jones & Bartlett tion in pleuralLearning, pressure AtLLC end-exhalation, meaNOT FORsurements SALE OR DISTRIBUTION such as the pulmonary artery wedge Before bronchodilator pressure, pulmonary artery pressure, and central venous pressure are affected by the amount of PEEP transmitted to the pleural space, which is 30 determined by lung compliance and chest wall © Jones & Bartlett Learning, © Jones & Bartlett Learning, LLC Expiration LLC compliance In patients with normal chest NOT FOR SALE OR DISTRIBUTION NOT FOR SALE wall compliance (over 150 mL/cm H 2O)OR andDISTRIBUTION 15 decreased lung compliance (under 50 mL/cm Volume (mL) H2O), less than one-fourth of the alveolar pressure 200 400 600 900 is transmitted to the pleural space In addition to esophageal pressure measure–15Jones & Bartlett Learning, LLC © © Jones & Bartlett Learning, LLC ments, changes in the pleural pressure can also be NOT FOR SALE OR DISTRIBUTIONInspiration NOTthrough FOR SALE OR of DISTRIBUTION estimated observation the respiratory –30 variation in the thoracic vascular catheter pressure measurements (i.e., the central venous –45 pressure, pulmonary artery pressure, and pulmonary artery occlusion pressure) With a stiff © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC –60 chest wall, the esophageal pressure or vascular NOT FOR SALE OR DISTRIBUTION NOT FORpressure SALE OR DISTRIBUTION shows greater fluctuation during the FIGURE 22–34 Flow–volume loops showing a response to bronchodilator 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 Flow (L/min) 45 Ventilation WB Saunders; 2001:17 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Patient–Ventilator Interactions: NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Synchrony and Asynchrony In patients with obstructive lung disease, it may be useful to monitor the flow–volume curve during mechanical ventilation (Figure 22–34) The flow–volume curve may © Jones Bartlett Learning, LLC provide insight&into the severity of airflow obstruction andNOT response to bronchodilator administration.90 FOR SALE OR DISTRIBUTION During any patient-triggered breath, the patient’s effort must interact with the ventilator’s gas delivery algorithm These interactions are considered synchronous when © Jones & Bartlett Learning, LLC ventilator flow is in phase with patient effort In contrast, NOT FOR SALE asynchronous interactions occur OR whenDISTRIBUTION these processes are out of phase At its worse, asynchrony appears as if Hemodynamics the patient is fighting or bucking the ventilator However, asynchrony often is much more subtle Failure of Because positive pressure ventilation can affect cardiac the patient to breathe in synchrony with the ventilator function, it is important to assess hemodynamics during © Jones & mechanical Bartlett Learning, © Jones & Bartlett Learning, LLC both the work of decreases patient comfort and increases ventilation AtLLC a minimum, the arterial blood NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION breathing and the oxygen cost of breathing Asynchrony pressure and heart rate should be measured frequently often leads to increased sedation needs and has been When the high airway pressures needed to support oxyassociated with longer time on mechanical ventilation.91,92 genation adversely affect cardiac performance, hemodyAsynchrony can be categorized as trigger asynchrony, namics may need to be supported with fluid, inotropes, flow asynchrony, cycle asynchrony, and mode asynchrony and pressors The role of the pulmonary artery cath© Jonesis & Bartlett Learning, LLC ©when Jones & Bartlett Learning, LLC Trigger asynchrony occurs the patient has difeter in mechanical ventilation unclear, and its use has NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR ficulty triggering the ventilator or the ventilator auto- DISTRIBUTION declined in recent years triggers The ventilator trigger sensitivity should be as It is important to appreciate the effect of positive pressensitive as possible without causing auto-triggering sure ventilation on hemodynamic assessments During Inability of the patient to trigger can be caused by positive pressure ventilation, pleural pressure increases an insensitive trigger setting on the ventilator, which during inhalation by an amount determined by lung © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, can be corrected by reduction of the pressure orLLC flow compliance and chest wall compliance:89 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION required for the patient to trigger the ventilator Inabil⌬Ppl/⌬Pplat ϭ Cl / (Cl ϩ Ccw) ity to trigger also can be due to respiratory muscle weakness Perhaps the most common cause of failure to where ⌬Ppl is the change in pleural pressure, ⌬Pplat trigger is auto-PEEP in patients with obstructive airway is the change in alveolar pressure, Cl is lung comdisease As noted earlier, auto-PEEP can be reduced by pliance, and Ccw is chest wall compliance By con© Jones & vention, Bartletthemodynamic Learning, LLC © Jones & Bartlett Learning, LLC the I:E ratio, or lowering minute ventilation, shortening measurements are made at NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION reducing airway obstruction through administration of end-exhalation (i.e., when transpulmonary pressures © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 488 CHAPTER 22 Mechanical Ventilation bronchodilators and clearing of secretions Using PEEP by adjusting the trigger sensitivity Other causes of auto- © Jones & Bartlett Learning, © Jones &toBartlett Learning, LLCand thus reduce the trigcounterbalance auto-PEEP triggering include excessive waterLLC condensation in the NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR can DISTRIBUTION gering load be effective for patients with COPD, ventilator circuit and leaks 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, care must be taken to not meet the patient’s inspiratory flow demand Lack © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC avoid hyperinflation with the PEEP When the attempt of synchrony can be detected by evaluating the airway NOT FOR SALE OR DISTRIBUTION FOR SALE OR DISTRIBUTION is to counterbalance auto-PEEP with PEEP, the clinician pressure waveform With NOT asynchrony, the pressure 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 should be suspected asynchrony is to compare patient-triggered breaths © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Another form of trigger asynchrony is auto-triggerwith a breath delivered via the manual breath control NOT FOR SALE OR DISTRIBUTION FORofSALE OR DISTRIBUTION ing Auto-triggering causes the ventilator to trigger in ComparingNOT the shape the mandatory and spontaresponse 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 Paw (cm H2O) Pes (cm H2O) Flow (L/min) 40 © Jones & Bartlett Learning, LLC 30 NOT FOR SALE OR DISTRIBUTION 20 10 –10 –20 –30 –40 –50 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 24 20 16 12 © 4Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION –4 –8 10 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 12 14 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 10 12 14 Time (s) (A) Flow (L/min) © Jones & Bartlett Learning, LLC 60 OR DISTRIBUTION NOT FOR SALE 50 40 30 20 10 –10 –20 –30 –40 –50 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Paw (cm H2O) Pes (cm H2O) © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 10 12 14 40 ©30Jones & Bartlett Learning, LLC 20 NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 10 10 12 14 Time (s) (B)Bartlett Learning, LLC © Jones & © Jones & Bartlett Learning, LLC FIGURE 22–35 OR (A) TheDISTRIBUTION inspiratory effort of the patient is not met by fixed NOT flow fromFOR the ventilator during pressure control ventilation The dashed line NOT FOR SALE SALE OR DISTRIBUTION 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 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Monitoring the Mechanically Ventilated Patient patient effort literally sucks the airway pressure graphic 489 is necessary to bring a patient into synchrony with the © Jones & Bartlett LLC © Jones &downward) Bartlett Learning, Clinical signsLLC of asynchrony include tachyventilator, propofolLearning, may be useful When ventilation NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION pnea, retractions, and chest-abdominal paradox Flow requires long inspiratory times and high airway pres- Inhalation Exhalation Flow (L/min) Pressure (cm H2O) Flow Pes Paw Volume (cm H2O) (cm H2O) (L) Flow (L/s) 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 increase in the pressure setting or the rise time set© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ting during PCV or PSV However, asynchrony can 95 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION also occur with PCV (Figure 22–36) For patients 0.8 who have a high respiratory drive because of anxiety or pain, flow asynchrony may be improved by appropriate use of sedation or analgesia.95 Cycle asynchrony occurs when the neural inspira30 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC tory time of the patient does not match the inspiraNOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION tory time setting on the ventilator If the inspiratory time is too short, the patient might double-trigger 40 the ventilator (Figure 22–37) During volume control ventilation, this can cause breath stacking, such that the patient is effectively receiving a tidal volume © Jones & twice Bartlett Learning, LLC © Jones & Bartlett Learning, LLC what is set If the inspiratory time is too long, Time (s) NOT FOR SALE ORwill DISTRIBUTION NOT FOR SALE OR DISTRIBUTION the patient actively exhale against the ventilator- FIGURE 22–36 Patient–ventilator 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 the pressure support © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC level, by an increase in the termination flow NOT FOR SALE OR NOT FOR SALE OR DISTRIBUTION setting on newer-generation ventilators, or DISTRIBUTION by use of pressure control instead of pressure support (pressure control causes inspiration Time to be time cycled rather than flow cycled) Cycle asynchrony is recognized as activation © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC of the expiratory (abdominal) muscles during FOR phase; SALEthis ORcan DISTRIBUTION NOT FOR SALE OR DISTRIBUTION theNOT inspiratory be detected clinically by palpation of the patient’s abdoFIGURE 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 & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Mode asynchrony occurs when the ventilaNOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION tor delivers different breath types With SIMV, 30 for example, some breath types are mandaPressure spike tory and others are spontaneous Because the patient’s respiratory center cannot adapt to varying breath types, asynchrony can develop © Jones & Bartlett LLC © Jones & Bartlett Learning, LLC –10 between the patient and the ventilator Another Learning, FOR 10 12 DISTRIBUTION NOT FOR SALE OR DISTRIBUTION NOT SALE OR form of mode asynchrony occurs with adap60 tive pressure control, in which the ventilator Flow = 35 L/min reduces support when the patient’s efforts result in a tidal volume that exceeds the set tidal volume.49,97 © Jones & Bartlett Learning, LLC –60 NOT FOR SALE OR DISTRIBUTION Sedation © Jones & Bartlett Learning, LLC NOT FOR6 SALE 7OR DISTRIBUTION 12 10 Time (s) Anxiety is a common cause of failure to breathe in synchrony with the ventilator In casesLearning, pharmacologic support may be © Jones & these Bartlett LLC necessary in the form of analgesics (narcotNOT FOR SALE OR DISTRIBUTION ics), sedatives (benzodiazepines), or (rarely) paralyzing agents When short-term sedation FIGURE 22–38 Airway pressure and flow waveforms illustrating active exhalation during pressure support ventilation Note that the flow does not decelerate to the flow termination criterion of the ventilator (5 L/min for this specific ventilator) Also note the presence of © spike Jones Learning, a pressure at the& endBartlett of each inspiration, indicatingLLC that the ventilator is pressure cycling rather flow cycling Modified Branson RD Modes of ventilator operation In: NOTthan FOR SALE OR from DISTRIBUTION MacIntyre NR, Branson RD, eds Mechanical Ventilation Philadelphia: WB Saunders; 2000 Copyright Elsevier 2000 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 490 CHAPTER 22 Mechanical Ventilation It must be remembered that all forms of respiratory severe acidosis, provided that the Pplat does not exceed © Jones Bartlett Learning, LLCto control pH The © Jones &suppression Bartlett Learning, LLC 30 cm & H2O Respiratory rate is adjusted are associated with adverse side effects It NOT FOR SALE OR DISTRIBUTION NOT FOR SALE DISTRIBUTION potential for air trapping in parenchymal lung injury is low is most OR important that disconnect alarms be properly if the breathing frequency is less than 35 breaths/min set when the patient’s ability to breathe spontaneAn increased inspiratory time, and even inverse ratio venously is pharmacologically suppressed Significant tilation (e.g., APRV), can be used to increase Pao2 with problems with pharmacologic suppression of respirarefractory hypoxemia The mechanisms for improved tion have been reported, such as long-term respira© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC oxygenation with inverse ratio ventilation include longer tory muscle weakness after use of paralyzing agents 98,99 NOT FOR SALE OR DISTRIBUTION FOR SALE gas mixing time, recruitmentNOT of slowly filling alveoli,OR andDISTRIBUTION during mechanical ventilation It has been shown development of auto-PEEP that assessment of the patient’s response to a daily Although imaging or mechanical techniques to trial of sedation cessation significantly reduces the guide proper PEEP settings have physiologic appeal, days of mechanical ventilation.100 This suggests that they are technically challenging and not practical for many mechanically ventilated patients are excessively © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC routine use Thus, most clinicians rely on various gas sedated and that this excessive sedation prolongs the 100,101 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE exchange criteria to guide PEEPOR andDISTRIBUTION Fio2 titrations course of mechanical ventilation This involves the use of algorithms designed to provide adequate oxygenation (Pao2 55 to 80 mm Hg or Spo2 of 88% to 95%) while minimizing Fio2 An example would Choosing Ventilator Settings for be the National Institutes of Health’s ARDS Network Forms LLC of Respiratory © Jones & Different Bartlett Learning, © Jones & Bartlett Learning, LLC PEEP/Fio algorithm ( Figure 22–39 ) 12,103 Note that NOT FOR SALE OR DISTRIBUTION NOTthis FOR SALE2 algorithm OR DISTRIBUTION Failure PEEP/Fio attempts to balance pressure administration (PEEP) with Spo2 or Pao2 and with Fio2 ALI and ARDS (Parenchymal Lung Injury) Randomized controlled trials have compared various With ALI and ARDS, lung compliance is low and lung volgas exchange strategies for setting PEEP in conjuncume is decreased It is important to realize, however, that tion with low Vt strategies and have reported that both there are often marked regional differences in the degree © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC aggressive (i.e., 13 to 15 cm H2O PEEP) and conservaof alveolar involvement Whereas some alveoli may be colNOT FOR SALE OR DISTRIBUTION NOT FOR OR DISTRIBUTION tive (i.e., to cm H2O) approaches haveSALE comparable lapsed or consolidated, others may be hyperinflated and 103–105 outcomes 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 2 to the healthier& regions of theLearning, lungs, resulting in potential © Jones Bartlett LLC ©not Jones & Bartlett Learning, LLC of PEEP are beneficial (and may produce harm) in forNOT regional overdistention injury Parenchymal injury can FOR SALE OR DISTRIBUTION NOT SALE OR DISTRIBUTION 105,106 patients with ALI FOR (Pao2/Fio Ͼ 200 mm Hg) also affect the airways, which can contribute to reduced Some mechanical approaches to setting PEEP are regional ventilation to injured lung units Gas exchange practiced in ICUs where the staff has considerable experiabnormalities 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 presand shunts LLC The low-V/Q regions result in © Jones & mismatching Bartlett Learning, © Jones & Bartlett LLCpoint of the presи regions result in increased sure greater than theLearning, lower inflection hypoxemia, and the high-Vи/Q 83 DISTRIBUTION NOT FOR SALE OR DISTRIBUTION NOTsure–volume FOR SALE OR curve, and the best stress index.84 PEEP dead space and hypercarbia should be avoided that results in a Pplat above 30 cm H2O Frequency–tidal volume settings for ALI and ARDS 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 & Bartlett Learning, © Jones & Bartlett Learning, LLC Lower PEEP Strategy LLC most convincingly demonstrated NOT 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 8 10 10 10 12 14 14 14 16 18 18–24 in mortality with a ventilator strategy using a Vt of mL/kg ideal body (A) 12 weight compared with 12 mL/kg © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Higher PEEP Strategy Thus, initial Vt should 6 mL/kg NOT FOR SALEbeOR 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 10 12 14 14 16 16 18 20 22 22 22 24 PEEP the Vt if Pplat, adjusted for the effect of excessive chest wall stiffness, (B) 30 cm H2O The LLC Vt can be FIGURE 22–39 (A)©Low-PEEP © Jones & exceeds Bartlett Learning, Jones & Bartlett LLC strategy used in the Learning, ARDSnet study (B) High-PEEP strategy used increased to as much as 8  mL/kg in the ARDSnet study.NOT In eachFOR case, combinations of PEEP and FIO2 were used to maintain a PaO2 NOT FOR SALE OR DISTRIBUTION SALE OR DISTRIBUTION if there is marked asynchrony or of 55 to 80 mm Hg or SpO2 of 88% to 95% © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Ventilatory Support Involves Trade-Offs lung recruitment can be demonstrated In the setting of 491 mechanical disadvantage, which further worsens muscle © Jones & Bartlett Learning, LLC © Jones &refractory Bartletthypoxemia, Learning,recruitment LLC maneuvers may be function Overinflated regions may also compress more и matching NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION used, followed by a level of PEEP to maintain alveolar healthy regions of the lung, impairing Vи/Q recruitment When setting PEEP in patients with ALI or ARDS, the hemodynamic effects of the increased intrathoracic pressure should also be monitored Regions of air trapping and intrinsic PEEP also function as a threshold load to trigger mechanical breaths Noninvasive ventilation (NIV) is standard first-line therapy in patients with COPD and has been shown to © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC improve outcomes by reducing the need for endotraObstructive LungNOT Disease FOR SALE OR DISTRIBUTION NOT FOR in SALE OR DISTRIBUTION cheal intubation and improving survival this patient 108 Respiratory failure from airflow obstruction is due to population NIV has also been used in other forms of increases in airway resistance This increases the presobstructive lung disease (e.g., asthma, cystic fibrosis), sure required for airflow, which may overload inspirabut there is less evidence for better outcomes in these tory muscles, producing a ventilatory pump failure patient populations Invasive ventilatory support is usu© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC with spontaneous minute ventilation inadequate for ally reserved for those who fail NIV or in those in whom NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION gas exchange In addition, the narrowed airways create NIV is contraindicated regions of lung that cannot properly empty, and autoTidal volume should be sufficiently low (e.g., 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 airways resistance and the low elastic recoil pressure © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC with emphysema increase the potential for air trapping, NOT FOR SALE OR DISTRIBUTION NOTand FOR ORrange DISTRIBUTION thisSALE limits the of breath rates available PerBOX 22–6 missive hypercapnia may be an appropriate trade-off to limit overdistention The inspiratory time in obstructive lung disease is set as low as possible to minimize the Methods for Selecting PEEP development of air trapping As noted earlier, judicious Incremental PEEP: This © Jones & approach Bartlett Learning, LLC © Jones & Bartlett Learning, LLC application of PEEP (up to 75% to 85% of auto-PEEP) uses combinations of PEEP NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR109DISTRIBUTION can counterbalance auto-PEEP to facilitate triggering and Fio2 to achieve the desired Use of a low-density gas (e.g., helium–oxygen mixlevel of oxygenation or the tures [heliox]) is another technique that can be used to highest compliance decrease auto-PEEP Decremental PEEP: This approach with a high level of LLC © Jones begins & Bartlett Learning, PEEP (e.g., 20 cm H 2O), after NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Neuromuscular Disease which PEEP is decreased in a The risk of VILI is generally less in a patient with neurostepwise fashion until deremuscular 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 decrease in compliance comfort, maintain Learning, recruitment,LLC prevent atelectasis, © Jones & Bartlett Learning, LLC © Jones & Bartlett Stress index measurement: The and avoid hypercarbia that may adversely affect central NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION pressure–time curve is nervous system function However, tidal volume should observed during constantnot exceed 10 mL/kg, and Pplat should be kept below flow inhalation for signs 30 cm H2O.110 Low levels of PEEP are often beneficial for of tidal recruitment and preventing atelectasis If patients with neuromuscular overdistention disease develop ALI or ARDS, should be managed © Jones & Bartlett Learning, LLC © they Jones & Bartlett Learning, LLC Esophageal pressure measureusing ventilator strategies incorporating lower tidal volNOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR 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 presTrade-Offs and subsequently deter-LLC © Jones sure & Bartlett Learning, © Jones & Bartlett Learning, LLC the optimal level of PEEP To provide adequate support yet minimize VILI, mechanNOT FORmine SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 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 benthan the lower inflection efits of better gas exchange Accordingly, pH goals as point low as&7.15 and Pao as 55 mm Hg are © Jones & Bartlett Learning, LLC © Jones Bartlett Learning, LLC goals as low often considered acceptable if necessary NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONto protect the lungs from VILI.111 Ventilator settings are thus selected © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 492 CHAPTER 22 Mechanical Ventilation to provide an adequate, but not necessarily normal, a low Pimax may predict respiratory muscle fatigue © Jones & Bartlett Learning, LLC © Jones &level Bartlett Learning, LLC of gas exchange while meeting the goals of enough The Pimax is measured by attachment of an anerNOT FOR SALE OR DISTRIBUTION NOT FOR SALE DISTRIBUTION PEEP toOR maintain alveolar recruitment and avoidance oid manometer to the endotracheal or tracheostomy of a PEEP–tidal volume combination that unnecessarily overdistends alveoli at end-inspiration.103–106 This has led to ventilatory strategies such as permissive hypercapnia, permissive hypoxemia, and permissive atelectasis Liberation Ventilation tube The patient then forcibly inhales after maximum exhalation When the Pimax is measured, it is recommended that a unidirectional valve be used and that the airway be completely obstructed for 20 to 25 seconds © Jones & Bartlett Learning, LLC © Jones & Bartlett 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 from Mechanical However, if the patient has high airways resistance or An important aspect of the management of patients receiving mechanical ventilation is recognizing © Jones & Bartlett Learning, LLC when the patient is ready to be liberated from the ventilator NOT FOR SALE OR DISTRIBUTION and extubating the patient at that point Evidence-based clinical practice guidelines have been published related to liberation from mechanical ventilation; Box 22–7 lists the recommendations from these guidelines.112 © Jones & Bartlett Learning, LLC Respiratory Muscles NOT FOR SALE OR DISTRIBUTION 30 © Jones & Bartlett Learning, LLC 15 45 NOT FOR SALE OR DISTRIBUTION 60 B © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION C For successful liberation from the ventilator, the load 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 © Jones & muscles Bartlett LLC © Jones & Bartlett Learning, LLC on the muscles is excessive, if the areLearning, weak, or NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION if the duty cycle (the inspiratory time relative to total 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 A © Jones & Bartlett Learning, © Jones & Bartlett Learning, LLC muscle function Diminished respiratory LLC muscle funcFIGURE 22–41 The one-way valve system used to measure NOT ORofDISTRIBUTION NOT FOR SALE OR DISTRIBUTION tion may FOR also beSALE the result disease, disuse, malnumaximum inspiratory pressure The patient is connected at A, the trition, hypoxia, or electrolyte imbalance The clinical manometer (B) is connected at C, and the patient exhales through D Port E is occluded during the measurement In this way, maximum signs of respiratory muscle fatigue are tachypnea, abnorinspiratory pressure is measured at functional residual capacity mal respiratory movements (respiratory alternans and From Kacmarek RM, Cycyk-Chapman MC, Young PJ, Romagnoli 113 abdominal paradox), and an increase in Paco2 DM Determination of maximal inspiratory pressure: a clinical study © Jones & Bartlett © Jones & Bartlett Learning, LLC Because Learning, the maximumLLC inspiratory pressure (Pimax) literature review Respir Care 1989;34:868–878 Reprinted with NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION is a good indicator of overall respiratory muscle strength, permission Minute Ventilation Depressed Respiratory Drive © Jones & Bartlett Learning, LLC Pain and anxiety Sepsis NOT FOR SALE OR DISTRIBUTION Increased dead space Excessive feeding Load Capacity Sedative drugs © Brain stem lesion Increased Resistive Load Bronchospasm Secretions Jones & Bartlett Learning, Small endotracheal tube © LLC NOT FOR SALE OR DISTRIBUTION Increased Elastic Load Low lung compliance Low chest wall compliance Auto-PEEP Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Neuromuscular Disease Cervical spine injury Phrenic nerve injury Critical illness polyneuropathy Prolonged blockade © Jones &neuromuscular Bartlett Learning, LLC Hyperinflation (COPD) NOTMalnutrition FOR SALE OR DISTRIBUTION Electrolyte disturbance Primary neuromuscular disease Thoracic Wall Abnormality Flail chest © Jones & Bartlett Learning, LLC © Jones & Bartlett PainLearning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION FIGURE 22–40 Respiratory muscle performance is determined by the balance between the load that is placed on the respiratory muscles and the ability of the muscles to meet that load © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Liberation from Mechanical Ventilation 493 BOX 22–7 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Evidence-Based Guidelines for Discontinuing Ventilatory Support NOT FOR SALE OR DISTRIBUTION NOT FOR SALE 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 all possible ventilatory and nonventilatory issues should be an integral part of the venti© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC lator discontinuation process NOT FOR SALE OR DISTRIBUTION NOTshould FORundergo SALE OR DISTRIBUTION Recommendation 2: Patients receiving mechanical ventilation for respiratory failure 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 Recommendation 3: Formal discontinuation assessments for patients receiving mechanical ventilation for © Jones respiratory & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC failure should be performed during spontaneous breathing rather than while the patient is NOT FORstillSALE OR DISTRIBUTION SALE OR DISTRIBUTION receiving substantial ventilatory support An initial briefNOT periodFOR of spontaneous breathing 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 minutes should prompt consideration for permanent ventilator discontinuation © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Recommendation 4: The removal of the artificial airway from a patient who has successfully been NOT FOR SALE OR DISTRIBUTION NOTbe FOR OR DISTRIBUTION discontinued from ventilatory support should basedSALE on assessments 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 SBTs should be performed every 24 hours © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Recommendation 6: Patients receiving mechanical ventilation for respiratory failure who fail an SBT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION shouldNOT receive a stable, nonfatiguing, comfortable form of ventilatory support 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 healthprofessionals should be developed and implemented by intensive care units Protocols aimed © Jones care & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC at optimizing sedation also should be developed and implemented NOT FOR SALE OR9:DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Recommendation Tracheostomy should be considered after an initial period of stabilization 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, ©(often Jones & Bartlett Learning, LLC those with LLC marginal respiratory mechanics manifested as tachypnea) in whom a tracheostomy NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION tube having lower resistance might reduce the risk of muscle overload; those who may derive psychological 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 ventiJones Bartlettfailure Learning, LLC Jonesdependent & Bartlett Learning, LLC latory© support for& respiratory should not be considered permanently©ventilator NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION until months of ventilator liberation attempts have failed Recommendation 11: Critical care practitioners should familiarize themselves with facilities in their communities, or units in hospitals they staff, that specialize in managing patients who require prolonged dependence on mechanical ventilation Such familiarization should include reviewing published peer-reviewed data from those units, if available When medically stable for transfer, patients who © Jones have & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC failed ventilator discontinuation attempts in the intensive care unit should be transferred to NOT FORthose SALE OR DISTRIBUTION FOR SALE ORdiscontinuation DISTRIBUTION facilities that have demonstrated success and safety inNOT accomplishing ventilator 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 support: a collective task force facilitated by the American College of Chest Physicians; the American Association for Respiratory Care; Bartlett Learning, LLC © Jones & Bartlett Learning, LLC and the American College of Critical Care Medicine Chest 2001;120:375S–396S © Jones & NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 494 CHAPTER 22 Mechanical Ventilation low compliance, a Pimax of –20 cm H O may not be where Pbreath is the pressure required to generate a © Jones & Bartlett Learning, LLC © Jones &adequate BartlettforLearning, LLC unassisted breathing spontaneous breath The Pbreath can be determined NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION The respiratory muscles should be rested if fatigue with esophageal balloon 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 some inspiratory efforts ImporA number of factors should improved before an © Jones & Bartlett Learning, LLC © be Jones & Bartlett Learning, LLC tantly, total rest (i.e., no inspiratory muscle activity with attempt is made to liberate the patient from the ventilator NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION controlled mechanical ventilation) can also be harmful, (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 catlittle as 24 hours under these conditions.98 If respiratory 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 mL/kg), should be reduced before attempts are made to liberate respiratory © rate (Ͻ 30 breaths/min), minute ventilation © Jones & Bartlett Learning, LLC Jones & Bartlett Learning, LLC the patient from the ventilator This is done with provi(Ͻ 12 L/min), vital capacity (Ͼ 15 mL/kg), and the Pimax NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 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 diaphragmatic fatigue (Figure 22–42).115 The tension– Vt (in liters) An RSBI less than 105 has been used as time index is calculated as the product of the contractile predictive of successful ventilator liberation, and an RSBI © Jones & force Bartlett Learning, LLC © Jones & Bartlett Learning, LLC (Pdi/Pdi–max) and contraction duration (duty greater than 105 has been used to predict NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION failure An cycle, Ti/Ttot) This requires measurement of the mean increase in Vd/Vt (which should be less than 0.6) and an transdiaphragmatic pressure (Pdi), the transdiaphragincrease in Vиco2 and Vиo2 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 index over 0.15 is predicreported, however, no criterion is better predicting © Jones & Bartlett Learning, LLC © Jones & atBartlett Learning, LLC tive of respiratory muscle fatigue Measurement of the spontaneous breathing trial extubation readiness than a FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION transdiaphragmatic NOT pressure requires esophageal and (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 (PTI),116 which can be determined more readily with © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC equipment available in the critical care unit It is calcuNOT FOR SALE OR DISTRIBUTION NOTBOX FOR22–8 SALE OR DISTRIBUTION lated as follows: Criteria Assessed to Determine Readiness for Ventilator Discontinuation (Liberation) Evidence Learning, for some reversal © Jones & Bartlett Learning, LLC © Jones & Bartlett LLCof the cause for respiraNOT FOR SALE OR1.0DISTRIBUTION NOT FOR SALEunderlying OR DISTRIBUTION tory failure Adequate oxygenation (e.g., 0.8 Fatigue threshold Pao2/Fio2 ratio Ͼ 150 to 200; PEEP to cm H2O; Fatigue zone 0.6 © Jones & Bartlett Learning, LLC © Jones Fio2 Յ 0.4 to 0.5) and pH & Bartlett Learning, LLC (e.g., Ͼ 7.25) NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 0.4 Hemodynamic stability, as defined by the absence of Nonfatigue T Tdi 0.2 active myocardial ischemia zone and the absence of clinically © Jones0 & Bartlett Learning, LLC © Jones & hypotension Bartlett Learning, LLC significant (i.e., 0.2 0.4 0.6 0.8 1.0 requiring vasopressor NOT FOR SALE OR DISTRIBUTION NOT FOR no SALE 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 inspi0.15 to 0.18 From Grassino A, Macklem PT ratory effort Respiratory muscle fatigue and ventilatory failure TI / Ttot PTI ϭ (Pbreath/Pimax) ϫ (Ti/Ttot) © Jones & Bartlett Learning, LLC Ann Rev Med 1984;35:625–647 Reprinted with NOT FOR SALE permission OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Liberation from Mechanical Ventilation may result in prolonged stay on the ventilator.120 It also 495 studies allowed performance of the SBT with the patient © Jones & Bartlett Learning, LLC © Jones &isBartlett 124–126 importantLearning, to reduce or LLC temporarily discontinue sedaattached to the ventilator NOT FOR SALE OR DISTRIBUTION NOT FOR SALE DISTRIBUTION tion in OR preparation of ventilator liberation; this has The SBT can be performed with no positive pressure been reported to decrease both days of ventilation and mortality.100,121 applied to the airway, with a low level of CPAP (5 cm H2O), or with a low level of PSV (5 to cm H2O) Proponents of the CPAP approach argue that this maintains functional residual capacity at a level similar to that after Approaches to Liberation © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC extubation It is argued that, in a patient with obstructive Two prospective, randomized, trials comNOT FORcontrolled SALE OR DISTRIBUTION FOR SALEairway OR DISTRIBUTION lung disease, this low level NOT of CPAP maintains pared SIMV weaning (i.e., gradual reduction in mandapatency 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 Jones &Both Bartlett LLC © Jones & Bartlett Learning, LLC was©performed studiesLearning, reported that the majorheart Such patients may tolerate a CPAP trial but then ity NOT of patients were successfully extubated after the first 34 FOR SALE OR DISTRIBUTION NOT FOR OR extubated DISTRIBUTION develop congestive heart SALE failure when 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 Proponents of the low-level PSV approach argue © Jones & Although Bartlettnewer-generation Learning, LLCventilators feature modes © Jones & Bartlett Learning, LLC that this overcomes the resistance to breathing through intendedOR to facilitate weaning (e.g., SmartCare, adaptive NOT FOR SALE DISTRIBUTION NOTthe FOR SALE OR DISTRIBUTION artificial airway However, 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, extubation was similar to that seen with the endotracheal © isJones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC in which the patient removed from the ventilator, tube in place.127 Resistance through the artificial airway and humidified supplemental oxygen OR is provided NOT FOR SALE DISTRIBUTION NOT FOR SALE inspiOR DISTRIBUTION is affected by many factors, including the patient’s 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 to choose an appropriate level of pressure support to ©does Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC that not generate an aerosol should be used, such overcome tube resistance However, one study reported as NOT a heated passover Passive humidifiers FOR SALEhumidifier OR DISTRIBUTION NOT when FORthe SALE ORperformed DISTRIBUTION similar outcomes SBT was with a T (e.g., artificial noses, heat and moisture exchangers) 128 piece and with 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 Similar outcomes are likely with a 2-hour SBT or a RESPIRATORY RECAP conducted with© Jones & Bartlett Learning, LLC © Jones & Bartlett LLC 30-minute SBT.129 InLearning, the acute care setting, tolerance of out removal of Liberation from Mechanical NOT FOR SALE OR DISTRIBUTION NOTanFOR SALE OR DISTRIBUTION SBT of 30 minutes to hours duration should prompt Ventilation the patient from consideration for extubation For chronically ventilator» Regularly assess for the ventilator, and dependent patients with a tracheostomy, the length of liberation readiness this approach has each SBT is increased, with alternating periods of ven» Perform a spontaneous se veral adv antilatory support and SBT In this case, the goal may be breathing trial to assess tages No addi© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC readiness for extubation daytime liberation with nocturnal ventilation tional equipment » If a spontaneousNOT breathing FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION is required, and trial is not tolerated, assess Recognition of a Failed Spontaneous for causes of failure if the patient fails Breathing Trial » Do not use synchronized the SBT, ventilaintermittent mechanical A failed SBT is discomforting for the patient and may tory support can ventilation (SIMV) as a cardiopulmonary Commonly be quickly © Jones Bartlett Learning, LLC rees- induce significant © Jones & Bartlett distress Learning, LLC weaning & mode listed criteria for discontinuation of an SBT include tachytablished All the » UseFOR protocols to improve NOT SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION pnea (respiratory rate over 35 breaths/min for 5 minutes monitoring funcsuccessful liberation or longer); hypoxemia (Spo2 below 90%); tachycardia tions and alarms (heart rate over 140 beats/min or a sustained increase on the ventilator are available during the SBT, which above 20%); bradycardia (sustained decrease in the heart may allow prompt recognition that the patient is failing rate of over 20%); hypertension (systolic blood presSBT Most of the literature © Jones & the Bartlett Learning, LLC related to ventilator lib© Jones & Bartlett Learning, LLC sure over 180 mm Hg); hypotension (systolic blood eration studies using a traditional SBT, although several NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 496 CHAPTER 22 Mechanical Ventilation pressure under 90 mm Hg); and agitation, diaphore- or partial&ventilatory support Jones Bartlett Learning, LLC © Jones &sis, Bartlett Learning, LLC the last three factors © Full or anxiety In some patients Comfort NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION are not caused by SBT failure and can be appropriately treated with verbal reassurance or pharmacologic support When SBT failure is recognized, ventilatory support should be promptly reestablished Assess readiness © Jones & Bartlett Learning, LLC Disease resolution Adequate gas exchange Hemodynamic stability Ability to breathe Causes of Spontaneous Breathing NOT FOR SALE OR DISTRIBUTION Trial Failure Spontaneous breathing trial Determine cause of failure © Jones & Bartlett Learning, LLC NOT Fail FOR SALE OR DISTRIBUTION When an SBT fails, the reason should be identified Success and corrected before another SBT is performed There are a variety of physiologic and technical reaUpper airway patent? Evaluate for extubation risk? Learning, LLC sons why patients fail an SBT An excessive respiratory © Jones & Bartlett Learning, LLC © Jones Aspiration & Bartlett Able to clear secretions? muscle load may be the cause High airways resistance NOT FOR SALE OR DISTRIBUTION 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 cause respiratory © Jones & imbalance Bartlett may Learning, LLC muscle weakness © andJones extubation.& Bartlett Learning, LLC Inadequate levels of potassium, magnesium, phosNOT FOR SALE OR DISTRIBUTION 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 Figbe taken to avoid overfeeding, because excessive caloric ure 22–43 presents the elements of an effective protocol ingestion elevates carbon dioxide&production Failure of © Jones Bartlett Learning, LLC © Jonesbest & Bartlett LLC From these elements incorporating evidence, Learning, a any major organ system can result in failure to liberate specific protocol can be developed that meets the local NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR 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 delay liberation until Learning, appropriate management of Jones & Bartlett LLC © Jones & Bartlett Learning, LLC KEY POINTS cardiovascular status has occurred NOT FOR SALE OR DISTRIBUTION NOT FOR DISTRIBUTION • Efforts should beSALE made toOR avoid 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 the natural airway.LLC Key parameters include cough © Jones & protect Bartlett Learning, â Jones Bartlett Learning, LLC &Volume control ventilation maintains minute strengthOR andDISTRIBUTION the need for suctioning (i.e., suctioning NOT FOR SALE NOT FORventilation SALE OR DISTRIBUTION but allows airway pressure and plateau requirements exceeding every hours should preclude pressure to fluctuate extubation) Although the ability to follow commands is • Pressure control ventilation allows minute ventidesirable 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., thoseLearning, recover© Jones & Bartlett LLC © Jones & Bartlett Learning, LLC • Modes on modern ventilators include continuous ing from a COPD exacerbation), to NIV may NOT FORextubation SALE OR DISTRIBUTION NOT FOR SALE OR mandatory ventilation, synchronized intermit- DISTRIBUTION reduce the duration of mechanical ventilation.130–132 Extutent mandatory ventilation, pressure support bation to NIV can also be considered to prevent extubaventilation, continuous positive airway pressure, tion failure in patients at risk, such as those with COPD, adaptive pressure control, adaptive support vencardiac disease, or others at risk for extubation failure tilation, airway pressure release ventilation, tube However, NIV & is Bartlett generally not recommended © Jones Learning, LLCto rescue © Jones & Bartlett Learning, LLC compensation, proportional assist ventilation, 133,134 a failed If theDISTRIBUTION patient fails extubation, NOTextubation FOR SALE OR NOTadjusted FOR SALE OR DISTRIBUTION neurally ventilatory assist, and highconsideration should be given to emergent reintubation frequency oscillatory ventilation • The tidal volume should be set to avoid overdisVentilator Discontinuation (Weaning) tention lung injury: mL/kg PBW is a suggested Protocols initial setting © Jones & Ventilator Bartlett Learning, LLC © Jones & Bartlett Learning, LLC discontinuation (weaning) protocols have • The respiratory rate and I:E ratio are set to conNOT FOR SALE DISTRIBUTION NOT FORtrol SALE OR 2DISTRIBUTION become OR increasingly popular in recent years, and these the Paco and to avoid hemodynamic comprotocols typically are implemented by respiratory promise and auto-PEEP © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION References • The Fio initially should be set at and then 14 497 Webb HJH, Tierney DF Experimental pulmonary edema due Jonesto&intermittent Bartlettpositive Learning, LLC with high inflation © Jones & Bartlett Learning, pressure ventilation weaned per pulse LLC oximetry to maintain an Spo© pressures: protection by positive end-expiratory pressure Am NOT FOR SALE OR DISTRIBUTION NOT FOR SALEover OR88% DISTRIBUTION Rev Respir Dis 1974;110:556–565 • PEEP should be set to avoid alveolar derecruit15 Crotti S, Mascheroni D, Caironi P, et al Recruitment and derement for patients with ARDS and to counterbalcruitment during acute respiratory failure Am J Respir Crit Care Med 2001;164:131–140 ance auto-PEEP in patients with COPD 16 Mead J, Takishima T, Leith D Stress distribution in lungs: a • The following should be monitored in the model of pulmonary elasticity.©J Appl Physiol.&1970;28:596–608 © Jones & Bartlett Learning, LLC Jones Bartlett Learning, LLC mechanically ventilated patient: physical signs 17 Chiumello D, Carlesso E, Cadringher P, et al Lung stress and NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION and symptoms, blood gas measurements, lung strain during mechanical ventilation for acute respiratory dismechanics, hemodynamics, patient–ventilator tress syndrome Am J Respir Crit Care Med 2008;178:346–355 18 Vaporidi K, Voloudakis G, Priniannakis G, et al Effects of synchrony, and sedation respiratory rate on ventilator-induced lung injury at a con• The most important aspect of liberation stant Paco2 in a mouse model of normal lung Crit Care Med from mechanical ventilation is assessment for 2008;36:1277–1283 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC readiness 19 Rich BR, Reickert CA, Sawada S, et al Effect of rate and NOT FOR SALE OR DISTRIBUTION NOT SALE ORlung DISTRIBUTION • A spontaneous breathing trial identifies most inspiratory flowFOR on ventilator induced injury J Trauma 2000;49:903–911 patients who are ready for liberation from 20 Marini JJ, Hotchkiss JR, Broccard AF Bench-to-bedside review: mechanical ventilation microvascular and airspace linkage in ventilator-induced lung • The poorest outcomes from the ventilator disconinjury Crit Care (London) 2003;7:435–444 tinuation process have been reported with SIMV 21 Trembly L, ValenzaLearning, F, Ribiero SP, Li LLC J, Slutsky AS Injurious ven© Jones & Bartlett Learning, LLC â Jones & Bartlett For patients who not tolerate a spontanetilatory strategies increase cytokines and C-fos M-RNA expresNOT FOR SALEous ORbreathing DISTRIBUTION NOT FOR ORratDISTRIBUTION sionSALE in an isolated lung model J Clin Invest 1997;99:944–952 trial, ventilatory support should 22 Ranieri VM, Suter PM, Tortorella C, et al Effect of mechanical be reestablished and the cause of the failure ventilation on inflammatory mediators in patients with acute identified respiratory distress syndrome: a randomized controlled trial JAMA 1999;282:54–61 23 Slutsky AS, Trembly L Multiple system organ failure: is mechanJones & Bartlett Learning, LLC factor? 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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 associacute 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 mechan2007;35:1815–1820 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ics in the patient with obstructive lung disease Respir Care 111 Hickling KG, Walsh J, Henderson S, Jackson R Low mortality 2005;50:246–261 NOT FOR SALE OR DISTRIBUTION rate in adult respiratory distress syndrome low-volume, NOT FORusing SALE OR DISTRIBUTION 91 de Wit M, Miller KB, Green DA, et al Ineffective triggering pressure-limited ventilation with permissive hypercapnia: a propredicts 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 guide92 Thille AW, Rodriguez P, Cabello B, et al Patient-ventilator asynlines for weaning and discontinuing ventilatory support: a colchrony during assisted mechanical ventilation Intensive Care lective task force facilitated by the American College of Chest © Med Jones & Bartlett Learning, LLC © Jones & Bartlett 2006;32:1515–1522 Physicians; the American AssociationLearning, for RespiratoryLLC Care; 93.NOT Imanaka H, Nishimura M, Takeuchi M, et al Autotriggerand the American College of Critical Care Medicine Chest FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 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 vol114 Laghi F, D’Alfonso N, Tobin MJ Pattern of recovery from diaume assisted ventilation J Crit Care 2007;22:252–257 phragmatic fatigue over 24 hours J Appl Physiol 1995;79:539–546 95 Kallet RH, Campbell AR,LLC Dicker RA, et al Work of breathing 115 Stoller JK Physiologic rationale for resting the ventilatory © Jones & Bartlett Learning, © Jones & Bartlett Learning, LLC during lung-protective ventilation in patients with acute lung muscles Respir Care 1991;36:290–296 NOT FOR SALE OR NOT116 FOR SALE OR injury andDISTRIBUTION acute respiratory distress syndrome: a comparison Jabour ER, Rabil DM,DISTRIBUTION Truwitt JD, et al Evaluation of a new weanbetween 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? 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LLC © Jones & Bartlett Learning, LLC Crit Care 2008;12:238 making Crit Care Med 2006;34:2530–2535 FOR SALE ORBD,DISTRIBUTION FOR SALEMF, OR 100.NOT Girard TD, Kress JP, Fuchs et al Efficacy and safety of a 121 Kress JP,NOT Pohlman AS, O’Connor et al.DISTRIBUTION Daily interruption of paired sedation and ventilator weaning protocol for mechanisedative 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 Lan122 Esteban A, Frutos F, Tobin MJ, et al A comparison of four methcet 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 & Bartlett LLC mechanical ventilation: a ran© Jones & Bartlett Learning, criticallyLearning, ill patients receiving 123 Brochard L, Rauss A, Benito S, etLLC al Comparison of three domised Lancet 2010;375:475–480 methods of gradual from ventilatory support during NOT FOR SALE OR trial DISTRIBUTION NOT FOR SALE OR withdrawal DISTRIBUTION © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 500 CHAPTER 22 Mechanical Ventilation weaning from mechanical ventilation Am J Respir Crit Care on chronic respiratory failure: a prospective, randomized, con- © Jonestrolled & Bartlett © Jones & Bartlett Learning, LLC Med 1994;150:896–903 study Am JLearning, Respir Crit Care LLC Med 1999;160:86–92 124 Ely EW, Baker AM, Dunagan DP, et al Effect of the duration of 131 Nava S, Ambrosino N, Clini E, et al Noninvasive mechanical NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION mechanical ventilation on identifying patients capable of breathventilation 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 implemencontrolled 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 extuba126 Robertson TE, Mann Hyzy R,& et al MulticenterLearning, implemen© HJ, Jones Bartlett LLC tion N Engl J Med 2004;350:2452–2460 © Jones & Bartlett Learning, LLC tation of a consensus-developed, evidence-based, spontaneous 133 Keenan SP, Powers C, McCormack DG, Block G Noninvasive NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION breathing trial protocol Crit Care Med 2008;36:2753–2762 positive-pressure ventilation for postextubation respiratory dis127 Straus C, Louis B, Isabey D, et al Contribution of the endotratress: 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 spontaneous breathing trials with T-tube or pressure-support time and ventilator-associated pneumonia LLC Chest © Jones & Bartlett Learning, LLC ©incidence Jonesof & Bartlett Learning, ventilation Am J Respir Crit Care Med 1997;156:459–465 2000;118:459–467 FOR OR SALE OR DISTRIBUTION 129.NOT Esteban E, AliaSALE I, Tobin MJ, et al.DISTRIBUTION Effect of spontaneous breathing 135 Ely EW,NOT Meade FOR MO, Haponik EF, et al Mechanical ventilator trial duration on outcome of attempts to discontinue mechanical weaning protocols driven by nonphysician health-care profesventilation 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 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NOT FOR SALE OR DISTRIBUTION ... short, mechanical Indications for Mechanical ventilation is required when the patient’s capabilities to Ventilation ventilate the lung and/or effect gas transport across the Mechanical ventilation. .. whether mechanical ventilation Complications of Mechanical is needed, clinical judgment is as important as strict Ventilation adherence to absolute guidelines One indication for Mechanical ventilation. .. benign therapy, and mechanical ventilation is imminent acute respiratory it can & have major effects on theLLC body’s homeostasis failure; in such cases, initiating mechanical ventilation © Jones