High versus Low PEEP in ARDS
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《新英格兰医药杂志》
To the Editor: I wonder how the results of the National Heart, Lung, and Blood Institute ARDS Clinical Trials Network study (July 22 issue)1 would have looked if the recruitment maneuvers had been performed in all 276 patients who were assigned to a higher positive end-expiratory pressure (PEEP). These patients had a clinical outcome similar to that in the lower-PEEP group, although they had less favorable baseline characteristics (older age, a lower ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen [PaO2:FiO2], a higher rate of primary acute respiratory distress syndrome [ARDS] or acute lung injury [i.e., that due to pneumonia or aspiration], and a higher Acute Physiology, Age, and Chronic Health Evaluation score). The investigators stopped using the maneuvers after the first 80 patients because the "subsequent mean increase in arterial oxygenation was small and transient." Is it correct, however, to assess the validity of this decision simply on the basis of a possible improvement in oxygenation? Improved oxygenation depends not only on an increase in aerated lung regions but also on ventilation–perfusion matching and other factors. An improved clinical outcome probably does not depend solely on improved oxygenation. Were there any effects on biologic markers after the recruitment maneuvers, independent of improved oxygenation?
Andreas Perren, M.D.
Ospedale Regionale Bellinzona e Valli
6500 Bellinzona, Switzerland
andreas.perren@eoc.ch
References
The National Heart, Lung, and Blood Institute ARDS Clinical Trials Network. Higher versus lower positive end-expiratory pressures in patients with the acute respiratory distress syndrome. N Engl J Med 2004;351:327-336.
To the Editor: In his editorial regarding the ARDS Clinical Trials Network study, Dr. Levy1 states that PEEP "does lead to recruitment of previously collapsed alveoli" and that "lung regions recruited with PEEP may not completely collapse at end-expiration." However, the notion that PEEP promotes lung recruitment is not only counterintuitive; it is also a physical impossibility.
Lung recruitment during mechanical ventilation is an inspiratory phenomenon and, as such, is dependent on inspiratory pressures and end-inspiratory lung volume. At similar PEEP levels, lung recruitment is directly proportional to the tidal volumes used.2 As the term implies, the application of PEEP occurs during expiration, a phase when lung volume decreases while gas is exhaled. Therefore, PEEP does not and cannot recruit the lungs, since it is applied during the phase when the lungs are actually deflating. When applied at appropriate levels, PEEP may prevent the derecruitment of alveolar units previously recruited during the inspiratory phase.3
Alexandre T. Rotta, M.D.
Driscoll Children's Hospital
Corpus Christi, TX 78411
References
Levy MM. PEEP in ARDS -- how much is enough? N Engl J Med 2004;351:389-391.
Pelosi P, Goldner M, McKibben A, et al. Recruitment and derecruitment during acute respiratory failure: an experimental study. Am J Respir Crit Care Med 2001;164:122-130.
Rotta AT. Experimental demonstration video of the roles of PEEP and tidal volume during lung recruitment. (Accessed October 21, 2004, at https://www.ibackup.com/qmanager/servlet/share?key=7374183948946851aaaaaa.)
The authors reply: The clinical outcomes might have been better if all the patients in the higher-PEEP group had undergone recruitment maneuvers, but we believe otherwise. Differences in the mortality rate and in the number of ventilator-free days did not favor patients who underwent recruitment maneuvers as compared with those who did not. The effects of the recruitment maneuvers on arterial oxygenation were, on average, small and transient.1 Some patients had hypotension as a result of the maneuvers. These observations do not support the speculation that outcomes would have been better in a larger group of patients.
We agree that arterial oxygenation is not the only predictor of outcomes. In fact, in our previous trial,2 arterial oxygenation worsened but mortality decreased significantly in the group assigned to a lower tidal volume as compared with the group assigned to a traditional tidal volume. However, in our assessment of recruitment maneuvers, we monitored arterial oxygenation to assess lung recruitment, not to predict clinical outcomes. In most previous studies of recruitment maneuvers, investigators also monitored arterial oxygenation to demonstrate recruitment effects.3,4,5 Like most previous studies, ours showed highly variable and brief effects. We do not have sufficient data to assess the effects of recruitment maneuvers on biologic markers.
Roy Brower, M.D.
Johns Hopkins University
Baltimore, MD 21205
Alan Morris, M.D.
University of Utah
Salt Lake City, UT 84112
Neil MacIntyre, M.D.
Duke University
Durham, NC 27708
for the National Heart, Lung, and Blood Institute ARDS Clinical Trials Network
References
Brower RG, Morris A, MacIntyre N, et al. Effects of recruitment maneuvers in patients with acute lung injury and acute respiratory distress syndrome ventilated with high positive end-expiratory pressure. Crit Care Med 2003;31:2592-2597.
The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med 2000;342:1301-1308.
Grasso S, Mascia L, Del Turco M, et al. Effects of recruiting maneuvers in patients with acute respiratory distress syndrome ventilated with protective ventilatory strategy. Anesthesiology 2002;96:795-802.
Villagra A, Ochagavia A, Vatua S, et al. Recruitment maneuvers during lung protective ventilation in acute respiratory distress syndrome. Am J Respir Crit Care Med 2002;165:165-170. [Abstract/Full Text]
Foti G, Cereda M, Sparacino ME, De Marchi L, Villa F, Pesenti A. Effects of periodic lung recruitment maneuvers on gas exchange and respiratory mechanics in mechanically ventilated acute respiratory distress syndrome (ARDS) patients. Intensive Care Med 2000;26:501-507.
The editorialist replies: In his letter, Dr. Rotta describes the concept that PEEP promotes lung recruitment as "counterintuitive" and a "physical impossibility." This is a relatively common misunderstanding. The function of PEEP is to prevent alveolar and small-airway end-expiratory collapse. In addition, as Dr. Rotta correctly points out, lung recruitment during mechanical ventilation is an inspiratory phenomenon and is dependent on inspiratory pressures and end-inspiratory lung volume. As demonstrated in many studies, increasing levels of PEEP, at a fixed tidal volume, result in increased levels of end-inspiratory pressure and end-inspiratory volume.1,2 In this way, stepwise increases in PEEP levels can be used as a means of alveolar recruitment. The use of incremental increases in PEEP at fixed tidal volumes as a means of increasing recruitment at end-expiration has been extensively described.3,4,5 Because of the recent attention and studies that have evaluated the role of PEEP in preventing derecruitment during expiration, many clinicians do not realize that increasing levels of PEEP can also result in alveolar recruitment.
Mitchell M. Levy, M.D.
Brown University School of Medicine
Providence, RI 02906
References
Gattinoni L, Pelosi P, Crotti S, Valenza F. Effects of positive end-expiratory pressure on regional distribution of tidal volume and recruitment in adult respiratory distress syndrome. Am J Respir Crit Care Med 1995;151:1807-1814.
Richard JC, Brochard L, Vandelet P, et al. Respective effects of end-expiratory and end-inspiratory pressures on alveolar recruitment in acute lung injury. Crit Care Med 2003;31:89-92.
Gattinoni L, D'Andrea L, Pelosi P, Vitale G, Presenti A, Fumagalli R. Regional effects and mechanism of positive end-expiratory pressure in early adult respiratory distress syndrome. JAMA 1993;269:2122-2127.
Ranieri VM, Eissa NT, Corbeil C, et al. Effects of positive end-expiratory pressure on alveolar recruitment and gas exchange in patients with adult respiratory distress syndrome. Am Rev Respir Dis 1991;144:544-551.
Hickling K. Low tidal volume ventilation: a PEEP at the mechanisms of decruitment. Crit Care Med 2003;31:318-320.
Andreas Perren, M.D.
Ospedale Regionale Bellinzona e Valli
6500 Bellinzona, Switzerland
andreas.perren@eoc.ch
References
The National Heart, Lung, and Blood Institute ARDS Clinical Trials Network. Higher versus lower positive end-expiratory pressures in patients with the acute respiratory distress syndrome. N Engl J Med 2004;351:327-336.
To the Editor: In his editorial regarding the ARDS Clinical Trials Network study, Dr. Levy1 states that PEEP "does lead to recruitment of previously collapsed alveoli" and that "lung regions recruited with PEEP may not completely collapse at end-expiration." However, the notion that PEEP promotes lung recruitment is not only counterintuitive; it is also a physical impossibility.
Lung recruitment during mechanical ventilation is an inspiratory phenomenon and, as such, is dependent on inspiratory pressures and end-inspiratory lung volume. At similar PEEP levels, lung recruitment is directly proportional to the tidal volumes used.2 As the term implies, the application of PEEP occurs during expiration, a phase when lung volume decreases while gas is exhaled. Therefore, PEEP does not and cannot recruit the lungs, since it is applied during the phase when the lungs are actually deflating. When applied at appropriate levels, PEEP may prevent the derecruitment of alveolar units previously recruited during the inspiratory phase.3
Alexandre T. Rotta, M.D.
Driscoll Children's Hospital
Corpus Christi, TX 78411
References
Levy MM. PEEP in ARDS -- how much is enough? N Engl J Med 2004;351:389-391.
Pelosi P, Goldner M, McKibben A, et al. Recruitment and derecruitment during acute respiratory failure: an experimental study. Am J Respir Crit Care Med 2001;164:122-130.
Rotta AT. Experimental demonstration video of the roles of PEEP and tidal volume during lung recruitment. (Accessed October 21, 2004, at https://www.ibackup.com/qmanager/servlet/share?key=7374183948946851aaaaaa.)
The authors reply: The clinical outcomes might have been better if all the patients in the higher-PEEP group had undergone recruitment maneuvers, but we believe otherwise. Differences in the mortality rate and in the number of ventilator-free days did not favor patients who underwent recruitment maneuvers as compared with those who did not. The effects of the recruitment maneuvers on arterial oxygenation were, on average, small and transient.1 Some patients had hypotension as a result of the maneuvers. These observations do not support the speculation that outcomes would have been better in a larger group of patients.
We agree that arterial oxygenation is not the only predictor of outcomes. In fact, in our previous trial,2 arterial oxygenation worsened but mortality decreased significantly in the group assigned to a lower tidal volume as compared with the group assigned to a traditional tidal volume. However, in our assessment of recruitment maneuvers, we monitored arterial oxygenation to assess lung recruitment, not to predict clinical outcomes. In most previous studies of recruitment maneuvers, investigators also monitored arterial oxygenation to demonstrate recruitment effects.3,4,5 Like most previous studies, ours showed highly variable and brief effects. We do not have sufficient data to assess the effects of recruitment maneuvers on biologic markers.
Roy Brower, M.D.
Johns Hopkins University
Baltimore, MD 21205
Alan Morris, M.D.
University of Utah
Salt Lake City, UT 84112
Neil MacIntyre, M.D.
Duke University
Durham, NC 27708
for the National Heart, Lung, and Blood Institute ARDS Clinical Trials Network
References
Brower RG, Morris A, MacIntyre N, et al. Effects of recruitment maneuvers in patients with acute lung injury and acute respiratory distress syndrome ventilated with high positive end-expiratory pressure. Crit Care Med 2003;31:2592-2597.
The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med 2000;342:1301-1308.
Grasso S, Mascia L, Del Turco M, et al. Effects of recruiting maneuvers in patients with acute respiratory distress syndrome ventilated with protective ventilatory strategy. Anesthesiology 2002;96:795-802.
Villagra A, Ochagavia A, Vatua S, et al. Recruitment maneuvers during lung protective ventilation in acute respiratory distress syndrome. Am J Respir Crit Care Med 2002;165:165-170. [Abstract/Full Text]
Foti G, Cereda M, Sparacino ME, De Marchi L, Villa F, Pesenti A. Effects of periodic lung recruitment maneuvers on gas exchange and respiratory mechanics in mechanically ventilated acute respiratory distress syndrome (ARDS) patients. Intensive Care Med 2000;26:501-507.
The editorialist replies: In his letter, Dr. Rotta describes the concept that PEEP promotes lung recruitment as "counterintuitive" and a "physical impossibility." This is a relatively common misunderstanding. The function of PEEP is to prevent alveolar and small-airway end-expiratory collapse. In addition, as Dr. Rotta correctly points out, lung recruitment during mechanical ventilation is an inspiratory phenomenon and is dependent on inspiratory pressures and end-inspiratory lung volume. As demonstrated in many studies, increasing levels of PEEP, at a fixed tidal volume, result in increased levels of end-inspiratory pressure and end-inspiratory volume.1,2 In this way, stepwise increases in PEEP levels can be used as a means of alveolar recruitment. The use of incremental increases in PEEP at fixed tidal volumes as a means of increasing recruitment at end-expiration has been extensively described.3,4,5 Because of the recent attention and studies that have evaluated the role of PEEP in preventing derecruitment during expiration, many clinicians do not realize that increasing levels of PEEP can also result in alveolar recruitment.
Mitchell M. Levy, M.D.
Brown University School of Medicine
Providence, RI 02906
References
Gattinoni L, Pelosi P, Crotti S, Valenza F. Effects of positive end-expiratory pressure on regional distribution of tidal volume and recruitment in adult respiratory distress syndrome. Am J Respir Crit Care Med 1995;151:1807-1814.
Richard JC, Brochard L, Vandelet P, et al. Respective effects of end-expiratory and end-inspiratory pressures on alveolar recruitment in acute lung injury. Crit Care Med 2003;31:89-92.
Gattinoni L, D'Andrea L, Pelosi P, Vitale G, Presenti A, Fumagalli R. Regional effects and mechanism of positive end-expiratory pressure in early adult respiratory distress syndrome. JAMA 1993;269:2122-2127.
Ranieri VM, Eissa NT, Corbeil C, et al. Effects of positive end-expiratory pressure on alveolar recruitment and gas exchange in patients with adult respiratory distress syndrome. Am Rev Respir Dis 1991;144:544-551.
Hickling K. Low tidal volume ventilation: a PEEP at the mechanisms of decruitment. Crit Care Med 2003;31:318-320.