Conflict of Interest Declaration

Transcription

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2 Conflict of Interest Declaration I receive royalties for two books on critical care published by McGraw-Hill I do not receive financial support for research from any pharmaceutical, biotechnology or medical device company I do not serve as a consultant to or on the advisory board of any company

3 In early 2017, New York University organized a symposium to celebrate the 60th anniversary of the Nobel Prize awarded to Andre Cournand and Dickinson Richards, the last North American clinicians to receive the award

4 The following lecture is the presentation I made at this symposium

5 Cournand and Richards made seminal observations concerning the effect of positive-pressure ventilation on cardiac output

6 Cournand and Richards made seminal observations concerning the effect of positive-pressure ventilation on cardiac output, yet the link between physiology and mechanical ventilation is best made by a concept of another Frenchman: Claude Bernard s milieu intérieur

7 Cournand and Richards seminal observations effect of positive-pressure ventilation on cardiac output, yet the link between physiology and mechanical ventilation is best made by a concept of another Frenchman: Claude Bernard s milieu intérieur

8 Claude Bernard during experiment with collaborators in laboratory of Collège de France Léon-Augustin L'hermitte, Laboratory of Physiology, Sorbonne University, Paris (1889) Cournand and Richards seminal observations yet link between physiology and mechanical ventilation is best made by a concept of another Frenchman: Claude Bernard s milieu intérieur

9 Acute Respiratory Failure Patients consented to photo display Patients admitted to the ICU exemplify par excellence a disturbance in this milieu

10 J Appl Physiol 1951;4:77 Although respiratory failure is defined conventionally in terms of abnormal arterial blood gases hypoxia, hypercapnia these are rarely the reasons for institution of mechanical ventilation

11 Rohrer F. In: Handbuch der normalen und pathologischen Physiologie. Springer, Berlin,1925, vol 2, p Fritz Rohrer, University of Bern Instead, mechanical ventilation is typically instituted because of disturbances in the framework first articulated by Rohrer, and subsequently developed by Fenn, Otis and Rahn: derangements in respiratory mechanics leading to marked increases in work of breathing

12 Photo taken in 1963 Arthur Otis Hermann Rahn Wallace Fenn Instead, mechanical ventilation is typically instituted because of disturbances in the framework first articulated by Rohrer, and subsequently developed by Fenn, Otis and Rahn: derangements in respiratory mechanics leading to marked increases in work of breathing

13 Inspiratory Effort in Acute Respiratory Failure AJRCCM 1997;155:906 In patients who develop acute respiratory failure, inspiratory effort increases ~ 4 times above the normal value, and the increase is 6-fold in some patients

14 ARRD 1982;126:9 In such patients, the respiratory muscles account for 20% of total oxygen consumption and more than 50% in some patients ARRD 1982;126:9

15 ARRD 1982;126:9 In such patients, the respiratory muscles account for 20% of total oxygen consumption and more than 50% in some patients ARRD 1982;126:9

16 NEJM 1994;330:1056 The overriding objective of mechanical ventilation is to decrease oxygen cost of breathing, enabling precious oxygen stores to be rerouted from the respiratory muscles to other vulnerable tissue beds

17 NEJM 2001;344:1986 Patient work during mechanical ventilation is primarily determined by a physician's ability to align cycling of the machine with the rhythm of the patient's respiratory centers

18 The rhythm of breathing, however, exhibits considerable breath-to-breath variability

19 1954 Engstrom Ventilator In the 1950s, 60s and even 70s, neuromuscular blockers were administered to prevent patients from bucking against cycling of the ventilator

20 Schematic Representation of Internal Operation of ICU Ventilator In: Tobin, Principles and Practice of Mechanical Ventilation, 3 rd ed, 2012, p67 Today, almost all ventilator modes are cycled-on by a patient triggering the pneumatic system that delivers flow

21 Cycling-Rhythm Alignment Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 Problems in aligning the cycling of a ventilator with a patient's own rhythm of breathing may arise at three points: cycling-on function (triggering), post-trigger inflation, and cycling-off

22 Cycling-Rhythm Alignment Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 Problems in aligning the cycling of a ventilator with a patient's own rhythm of breathing may arise at 3 points: cycling-on (triggering), post-trigger inflation (flow delivery), and cycling-off function (inspiration: expiration switchover)

23 Cycling-Rhythm Alignment Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 Problems in aligning the cycling may arise at three points: cycling-on function (triggering), post-trigger inflation, and cycling-off function (inspiration:expiration switchover)

24 Respiratory Motor Output and Ventilator Unloading For a given trigger sensitivity, patient respiratory motor output determines the delay between onset of inspiratory effort and onset of ventilator unloading

25 Low Drive and Delayed Ventilator Assistance Flow Paw Pes When respiratory drive is low, assistance may not begin until well into a patient s inspiratory time, thereby causing the ventilator to cycle almost completely out of phase with the patient s respiratory cycle

26 Output Flow-Control Valve In: Tobin, Principles and Practice of Mechanical Ventilation, 3 rd ed, 2012, p69 When patient inspiratory effort opens the demand valve, the inspiratory neurons do not suddenly switch off, and a patient may expend considerable inspiratory effort throughout the remainder of inflation

27 Respiratory Motor Output and Ventilator Unloading Tobin NEJM 2001;344:1986 When patient inspiratory effort opens the demand valve, the inspiratory neurons do not suddenly switch off, and a patient may expend considerable inspiratory effort throughout the remainder of inflation

28 Intrinsic PEEP impedes Ventilator Triggering P es, cm H 2 O P aw, cm H 2 O Flow, L/m PEEPi = 0.5 cmh 2 O PEEPi 10.6 cmh 2 O Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 The patient on the right exhibits a considerable delay between the onset of inspiratory effort, signaled by the vertical blue line, and the onset of flow delivery by the ventilator, signaled by the vertical red line

29 Intrinsic PEEP impedes Ventilator Triggering P es, cm H 2 O P aw, cm H 2 O Flow, L/m PEEPi = 0.5 cmh 2 O PEEPi 10.6 cmh 2 O Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 The patient had to decrease esophageal pressure by more than 10 cm H 2 O, overcoming the level of intrinsic PEEP, in order to successfully trigger flow delivery by the ventilator

30 Failure to Trigger Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 Among patients receiving a high level of ventilator assistance, a quarter to a third of patient inspiratory efforts may fail to trigger the machine

31 Failure to Trigger Rate = 16 Rate = 28 Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 In this patient, the respiratory centers are firing 28 times per minute whereas the ventilator is cycling only 16 times per minute. That is, 43% of the patient s inspiratory efforts fail to trigger ventilator assistance.

32 Failure to Trigger Rate = 16 Rate = 28 Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 the respiratory centers are firing 28/min whereas ventilator is cycling only 16 times per minute. That is, 43% of the patient s inspiratory efforts fail to trigger ventilator assistance

33 Double Triggering Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 Some patients exhibit double triggering, where the ventilator produces two inflations within a single inspiratory effort made by the patient

34 Double Triggering Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 Here, esophageal pressure falls and remains negative for more than 1 second, whereas duration of mechanical inflation is 0.6 second

35 Double Triggering Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 The longer duration of neural inspiration as compared with mechanical inflation causes the ventilator to deliver a 2 nd breath before there s time for exhalation, producing breath stacking

36 Double Triggering Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 In this patient, arrowheads signal 4 incidents of double triggering; the width of the Pes swing is roughly equivalent to duration of patient neural inspiratory time

37 Double Triggering Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 On the bottom tracing, patient neural inspiratory time in the double-triggered breaths width of the Pes swing is substantially longer than in the normally triggered breaths

38 Triggering Peculiarities Some might think that these triggering peculiarities are no more than arcane quirks; on the contrary, they have major significance and contribute to patient mortality when they go unrecognized

39 Proportion Surviving Low versus High Tidal Volume in ARDS Low, 6 ml/kg Control, 12 ml/kg Survival 69% 60% 0.2 n=861 (p<0.007) Days after Randomization NEJM 2000;342:1301 Consider mechanical ventilation in patients with ARDS, where a tidal volume of 6 ml/kg has been shown to lower mortality

40 Tidal Volume in ARDS This setting is so widely accepted that it has become de rigueur in protocolized management

41 Tidal Volume in ARDS Principles and Practice of Mechanical Ventilation, 3 rd ed, 2012, p141 Protocol advocates, ungrounded in physiology, do not recognize that low tidal volume is necessarily accompanied by shortening of mechanical inspiratory time; and once mechanical TI becomes less than neural TI, double triggering is inevitable

42 Tidal Volume in ARDS accompanied by shortening of mechanical TI; and once mechanical inspiratory time becomes less than neural inspiratory time, double triggering is inevitable Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871

43 Proportion Surviving Low versus High Tidal Volume in ARDS Low, 6 ml/kg Control, 12 ml/kg Survival 69% 60% 0.2 n=861 (p<0.007) Days after Randomization NEJM 2000;342:1301 Protocol enthusiasts believe they re delivering a tidal volume of 6 ml/kg, but the patient is receiving 12 ml/kg a setting proven to increase mortality

44 There is simply no substitute for deep understanding and clinical wisdom when taking care of patients Dickinson W. Richards, MD

45 Inspiratory Flow Demand Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 When patients are initially connected to a ventilator, inspiratory flow is typically set at some default value, such as 60 L/min; many critically ill patients have elevated respiratory motor output and the flow setting may not be sufficient to meet patient flow demands

46 Inspiratory Flow Demand Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 The flow setting at 60 L/min in this patient produced marked negative deflection in airway pressure (the triggering effort); subsequent extensive scalloping of the pressure contour signifies that delivered flow was insufficient to meet the patient's high demand

47 Inspiratory Flow Demand Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 A flow setting at 90 L/min resulted in a small negative deflection in airway pressure and a smooth convex pressure contour, signifying that flow satisfied patient respiratory motor output

48 Inspiratory Flow Demand Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 The swings in esophageal pressure were smaller at flow of 90 L/min, signifying greater unloading of the respiratory muscles

49 Cycling-Rhythm Alignment Tobin et al, Comprehensive Physiology (Handbook of Physiology) 2012;2:2871 The next point in the respiratory cycle at which problems may arise is at the switchover between inspiration and expiration

50 Inspiration-Expiration Switchover Neuronal firing During pressure support, the algorithm for "cycling-off" of mechanical inflation is based on a decrease in flow to 25% of the peak value

51 Inspiration-Expiration Switchover Neuronal firing In patients with COPD who have a prolonged time constant, more time will be required to reach this threshold

52 Inspiration-Expiration Switchover Neuronal firing The expiratory neurons become impatient and start to fire, causing contraction of the expiratory muscles during mechanical inflation

53 Inspiration-Expiration Switchover Pes, cm H 2 O Time, sec We became aware of this problem by looking at the contour of esophageal pressure in patients with COPD receiving pressure support

54 Inspiration-Expiration Switchover Pes, cm H 2 O Esophageal pressure Time, sec Halfway during inflation, esophageal pressure is higher than calculated chest-wall recoil pressure (the dashed tracing), indicating expiratory muscle recruitment

55 Expiratory Muscle Recruitment during Inflation Transversus abdominis EMG (arbitrary units) To obtain more direct evidence, we inserted needle electrodes into the transversus abdominis

56 Expiratory Muscle Recruitment during Inflation Transversus abdominis EMG (arbitrary units) This patient with COPD receiving pressure support activated his expiratory muscles about half way during mechanical inflation an under-appreciated form of fighting the ventilator

57 Cycling-Rhythm Alignment Ventilator Subject 1 phase angle (θ): 60 Subject 2 phase angle (θ): -45 The most precise way to quantify a discrepancy in timing of ventilator cycling versus rhythmical activity of a patient's respiratory centers is to measure phase angle (θ)

58 Cycling-Rhythm Alignment Ventilator Subject 1 phase angle (θ): 60 Subject 2 phase angle (θ): -45 If, for example, the major expiratory muscle, the transversus abdominis, starts to contract before completion of mechanical inflation, phase angle will have negative units

59 Cycling-Rhythm Alignment We employed a Starling resistor to induce airflow limitation in healthy subjects and wire electrodes to obtain EMG recordings of the diaphragm and transversus abdominis

60 Cycling-Rhythm Alignment All subjects exhibited non-triggering efforts when ventilated with pressure support

61 Cycling-Rhythm Alignment Phase angle of non-triggering attempts was significantly more negative than phase angle of attempts that successfully triggered the ventilator

62 Cycling-Rhythm Alignment This means that the length of time that the expiratory muscles had been active before cycling-off of mechanical inflation was longer for non-triggering attempts than for triggering attempts

63 Cycling-Rhythm Alignment The longer the time that mechanical inflation continues into neural expiration, the shorter will be the time available for unopposed expiratory flow, causing elastic recoil to rise and increasing the likelihood of non-triggering

64 Sleep during Mechanical Ventilation By ablating behavioral stimuli, sleep might be expected to enhance respiratory muscle rest during mechanical ventilation

65 Sleep during Mechanical Ventilation But again physiological mechanisms intervene

66 Sleep during Mechanical Ventilation Assist Control Pressure Support Horizontal bars on top signify arousals and awakenings We undertook polysomnography in critically ill patients receiving assist-control and pressure support

67 Sleep during Mechanical Ventilation Assist Control Pressure Support Horizontal bars on top signify arousals and awakenings During pressure support, this patient had repeated central apneas

68 Apneas per hour Sleep during Mechanical Ventilation Assist Control Pressure Support More than half the patients developed central apneas during pressure support, but no apneas during assist-control

69 Arousals plus Awakenings per hour p< Assist Control Pressure Support Sleep fragmentation was greater during pressure support than during assist-control: 79 versus 54 events per hour

70 Arousals plus Awakenings per hour p< Assist Control Pressure Support This level of sleep fragmentation is equivalent to that experienced by patients with obstructive sleep apnea who have excessive daytime sleepiness and impaired cognition

71 Sleep during Mechanical Ventilation Assist Control Pressure Support Horizontal bars on top signify arousals and awakenings Disturbed sleep during pressure support was related to the development of central apneas, which, in turn, was related to the difference between end-tidal PCO2 and the apnea threshold

72 Sleep during Mechanical Ventilation P ET CO 2 minus apnea threshold, mm Hg Central apneas per hour Disturbed sleep during pressure support was related to the development of central apneas, which, in turn, was related to the difference between end-tidal PCO2 and the apnea threshold

73 Sleep during Mechanical Ventilation 90 Apneas per hour 75 Arousals plus Awakenings per hour p< Pressure Support PS plus Dead Space 0 Pressure Support PS plus Dead Space The addition of dead space increased PCO 2 by 4.3 mm Hg and decreased central apneas (from 53 to 4 per hour), and decreased the sum of arousals and awakenings from 79 to 44 events per hour

74 Sleep during Mechanical Ventilation 90 Apneas per hour 75 Arousals plus Awakenings per hour p< Pressure Support PS plus Dead Space 0 Pressure Support PS plus Dead Space The addition of dead space increased PCO 2 by 4.3 mm Hg, decreased central apneas (from 53 to 4 per hour), and decreased the sum of arousals and awakenings from 79 to 44 events per hour

75 Physiologic Basis of Mechanical Ventilation Tobin NEJM 2001;344:1986 In summary, understanding of respiratory physiology is fundamental to achieving optimal synchronization of respiratory muscle groups with ventilator cycling and achieving muscle rest, which is the primary reason mechanical ventilation is instituted

76 Dr. E. B. Mer Dr. Protocol Some physicians, however, do not relish a physiological (individualized) approach to mechanical ventilation, and prefer Making Everything Easier guidelines

77 While mechanical ventilation saves many lives, it is also responsible for many deaths

78 Accordingly, it is critical to get patients off the ventilator at the earliest possible time

79 Getting Patients off the Ventilator This task demands greater wisdom and cognitive skill than is required for adjusting settings on the ventilator

80 60-80% of Ventilated Patients Tolerate First Weaning Attempt Percentage Extubated Reintubated % 68% 20 16% 0 n = 456 n = 546 Brochard et al AJRCCM 1994 Esteban et al NEJM 1995 Randomized trials on weaning techniques reveal that physicians are inherently slow at initiating the weaning process

81 Weaning-Predictor Tests Weaning predictor tests consist of physiological measurements that alert a physician that a ventilated patient might be able to come off the ventilator sooner than the physician otherwise thinks

82 In this study, we developed a new weaning predictor test, frequency-to-tidal volume ratio, f/vt

83 Rapid Shallow Breathing Index Ventilator stopped Rapid shallow breathing is present when f/v T exceeds 100 breaths/min/liter e.g., f = 30 breaths/min V T = 0.30 liter When the f/vt ratio exceeds 100, rapid shallow breathing is present

84 f/vt Threshold N Engl J Med 1991;324:1445 A f/vt ratio of 100 performed superiorly to other weaning predictors in forecasting which patients would successfully tolerate a T-tube trial vs. patients who would fail a T-tube trial

85 f/vt: Predicting Weaning-Extubation Outcome Yang & Tobin, 1991 Gandia & Blanco, 1992 Sassoon & Mahutte, 1993 Yang, 1993 Mohsenifar et al, 1993 Lee et al, 1996 Capdevila et al, 1995 Epstein, 1995 Chatila et al, 1996 Dojat et al, 1996 Leitch et al, 1996 Mergoni et al, 1996 Bouachour et al, 1996 Baumeister et al, 1997 Гологорский et al, 1997 Jacob et al, 1997 Krieger et al, 1997 Rivera & Weissman et al, 1997 Farias et al, 1998 Vallverdu et al, 1998 Thiagarajan et al, 1999 Zeggwagh et al, 1999 Maldonado et al, 2000 Uusaro et al, 2000 Khamiees et al, 2001 Smina et al, 2003 Conti et al, 2004 Fernandez et al, 2004 Jiang et al, 2004 Since our original report, the accuracy of f/vt in predicting weaning outcome has been evaluated by more than 27 groups of investigators, making it the most reevaluated phenomenon in critical care

86 Positive Predictive Value ranges from 0.53 to 0.98 Positive Predictive Value Some investigators reported that f/vt was unreliable in predicting weaning outcome

87 Positive Predictive Value as a Function of Pretest Probability Positive Predictive Value Weighted r = p < Pretest Probability of Success Once the non-supportive data are analyzed using a Bayesian framework, anchored on pretest probability, they unwittingly confirm the reliability of f/vt

88 Weaning Trial Patient consented to photo display If f/vt is less than 100, the physician proceeds with a weaning trial using one of two methods: intermittent unassisted breathing (zero vent support, as with T-tube trial seen here) or gradual reduction in ventilator assistance

89 Weaning-Predictor Tests Patient consented to photo display Weaning predictors are not done to forecast a failed weaning trial, but in order to alert a physician that a patient might tolerate a weaning trial sooner than the physician otherwise thinks and move that weaning trial earlier in time and shorten the overall of duration mechanical ventilation

90 Weaning-Predictor Tests Patient consented to photo display Weaning predictors are not done to forecast a failed weaning trial, but in order to alert a physician that a patient might tolerate a weaning trial sooner than the physician otherwise thinks and move that weaning trial earlier in time and shorten the overall of duration mechanical ventilation

91 Weaning-Predictor Tests In: Tobin, Principles and Practice of Mechanical Ventilation, 3 rd ed, 2012, p1308 Weaning predictors are not done to forecast a failed weaning trial, but in order to alert a physician that a patient might tolerate a weaning trial sooner than the physician otherwise thinks and move that weaning trial earlier in time and shorten the overall of duration mechanical ventilation

92 AJRCCM 1994;150:896 In 1994, Brochard published the first RCT of different weaning methods, showing that IMV was the worst technique

93 AJRCCM 1994;150:896 One arm in the Brochard RCT was T-tube trials combined with assist-control, but the duration of rest between each failed T-tube trial could be as brief as 1 hour

94 Transdiaphragmatic twitch pressure At this time, Franco Laghi had data showing that recovery from diaphragmatic fatigue required at least 24 hours of rest

95 This was the motivation behind the incorporation of a 24-hour rest arm in an RCT conducted by the Spanish Lung Failure Collaborative Group

96 Our study revealed that T-tube trials combined with 24 hours of rest weaned patients 3 times faster than did IMV and 2 times faster than did pressure support

97 JAMA 2013;309:671 The most difficult group of patients to wean JAMA is those 2013;309::671 requiring prolonged ventilation in a long-term acute care hospital (LTACH)

98 Proportion of patients remaining on mechanical ventilation Trach Collar versus Pressure Support Pressure support Trach collar 0.0 p = Weaning duration (days) JAMA 2013;309:671 In a randomized trial, we found that intermittent unassisted breathing (using a tracheostomy collar) resulted in 1.43 times faster removal of the ventilator than did pressure support

99 Randomized Controlled Trials of Weaning Techniques The superior outcome with unassisted breathing arms (T-tube, trache collar) in our two RCTs is best explained on the basis of physiology

100 Pressure Support vs Unassisted Breathing Pressure Support Unassisted Breathing Tobin et al, Comprehensive Physiology (Handbook of Physiology)2012;2:2871 The superior outcome with the unassisted-breathing arm (T-tube, trache collar) in our two RCTs is best explained on the basis of physiology

101 Pressure Support vs Unassisted Breathing Pressure Support Unassisted Breathing Tobin et al, Comprehensive Physiology (Handbook of Physiology)2012;2:2871 During trach-collar or T-piece trial, the amount of respiratory work is determined solely by the patient the ventilator cannot do any work

102 Evaluation of Patient Weanability Trach-Collar or T-piece Wean Respiratory Pump Ventilator During trach-collar or T-piece trial, the amount of respiratory work is determined solely by the patient the ventilator cannot do any work

103 Evaluation of Patient Weanability Trach-Collar or T-piece Wean Respiratory Pump Ventilator As such, a physician observing a patient breathe on a T-piece or trach collar has a completely clear view of the patient's respiratory capabilities

104 Evaluation of Patient Weanability Pressure-Support Wean Respiratory system Ventilator During pressure-support weaning, a clinician's ability to judge weanability is clouded because the patient is receiving ventilator assistance

105 P es, cm H 2 O Methodology to Quantify Pressure-Time Product during Pressure Support Onset Inspiratory Effort Esophageal pressure Chest-wall recoil pressure Time, sec Jubran et al, AJRCCM 1995;152:129 and it is extremely difficult to distinguish between how much work the patient is doing and how much work the ventilator is doing, even when esophageal pressure is being monitored and impossible without esophageal pressure monitoring

106 P es, cm H 2 O Methodology to Quantify Pressure-Time Product during Pressure Support Onset Inspiratory Effort Esophageal pressure Chest-wall recoil pressure Time, sec Jubran et al, AJRCCM 1995;152:129 and it is extremely difficult to distinguish between how much work the patient is doing and how much work the ventilator is doing, even when esophageal pressure is being monitored and impossible without esophageal-pressure monitoring

107 Evaluation of Patient Weanability Pressure-Support Wean Patient work Ventilator work It may be that the ventilator is doing a moderate amount of work

108 Evaluation of Patient Weanability Pressure-Support Wean Patient work Ventilator work Or the ventilator is doing a large amount of work

109 Evaluation of Patient Weanability Pressure-Support Wean Patient work Ventilator work Or the ventilator is doing very little work

110 Evaluation of Patient Weanability Pressure-Support Wean By physical examination, and even by looking at airway pressure tracings on the monitor, it is impossible to estimate how much work a patient is performing while receiving pressure support

111 Evaluation of Patient Weanability Trach-Collar or T-piece Wean Pressure-Support Wean Patient work Ventilator work Because of the impossibility of guesstimating work of breathing during pressure support, clinicians are more likely to accelerate the weaning process in patients who perform unexpectedly well during a T-piece trial or trach-collar challenge than when a low level of pressure support is being used

112 Readiness of a Patient for Extubation PS 0 PS 5 PS 10 Time (sec) Tobin et al, Comprehensive Physiology (Handbook of Physiology)2012;2:2871 Many physicians think weaning is complete when they reach pressure support of 5-7 cmh 2 O, often combined with PEEP 5 cmh 2 O, and extubate patients from these settings

113 Readiness of a Patient for Extubation PS 0 PS 10 Time (sec) Tobin et al, Comprehensive Physiology (Handbook of Physiology)2012;2:2871 When assessing a patient s readiness for extubation, a physician needs to guesstimate patient work of breathing

114 Patient work of breathing, Percent Decrease in Patient Work of Breathing Compared with Extubated State 1% Extubated CPAP 0, PS 0 (FlowBy) Compared with work of breathing in the extubated state, breathing through the ventilator circuit (with CPAP of 0 and pressure support of 0) decreases patient work by about 1%

115 Patient work of breathing, Percent Decrease in Patient Work of Breathing Compared with Extubated State 1% % ARRD 1991;143:469 AJRCCM 1995;152:129 Extubated CPAP 0, PS 0 (FlowBy) PS 5 CPAP 5 In contrast, CPAP of 5 decreases patient work of breathing by 40% Pressure support of 5 decreases patient work of breathing by 30-40%

116 Patient work of breathing, Percent Decrease in Patient Work of Breathing Compared with Extubated State 1% % ARRD 1991;143:469 AJRCCM 1995;152:129 Extubated CPAP 0, PS 0 (FlowBy) PS 5 CPAP 5 In contrast, CPAP of 5 decreases patient work of breathing by 40% Pressure support of 5 decreases patient work of breathing by 30-40%

117 Patient work of breathing, Percent Decrease in Patient Work of Breathing Compared with Extubated State 1% % ARRD 1991;143:469 AJRCCM 1995;152:129 Extubated CPAP 0, PS 0 (FlowBy) PS 5 CPAP 5 When evaluating a patient s readiness for extubation, the thing you most want to avoid is: A decrease in patient work of breathing compared to what it will be following extubation

118 Patient work of breathing, Percent Decrease in Patient Work of Breathing Compared with Extubated State 1% % ARRD 1991;143:469 AJRCCM 1995;152:129 Extubated CPAP 0, PS 0 (FlowBy) PS 5 CPAP 5 When evaluating a patient s readiness for extubation, the thing you most want to avoid is: A decrease in patient work of breathing compared to what it will be following extubation

119 Patient consented to photo display Readiness of a Patient for Extubation AJRCCM 2012;185:349 The vast majority of patients can cope with a 40-60% increase in work of breathing at the point of extubation but a fragile patient may not

120 Patient work of breathing, Percent Decrease in Patient Work of Breathing Compared with Extubated State 1% % ARRD 1991;143:469 AJRCCM 1995;152:129 Extubated CPAP 0, PS 0 (FlowBy) PS 5 CPAP 5 To extubate a fragile patient directly from CPAP of 5 or from pressure support of 5 is to risk killing that patient

121 In conclusion: over the breadth of my pulmonary and critical care practice,. Patient consented to photo display

122 Conclusion: Over the breadth of my pulmonary and critical care practice, no area demands greater understanding of physiological principles than ventilator management, and the need for physiological understanding is greatest in facilitating expeditious weaning while minimizing the risk of death

123 Physiologic Basis of Mechanical Ventilation PS 0 Time (sec) Over the breadth of my practice, no area demands greater understanding of physiological principles than ventilator management, and the need for physiological understanding is greatest when facilitating expeditious weaning and extubation while minimizing the risk of death

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