© 2006 American Thoracic Society
Is There a Safe Plateau Pressure Threshold for Patients with Acute Lung Injury and Acute Respiratory Distress Syndrome?From the Authors:We appreciate the comments of Drs. Jardin, Shiu, and Rosen regarding our Critical Care Perspective (1). We agree with Dr. Jardin's statement, "A plateau pressure of 30–35 cm H2O is not safe, because it is actually high!" We also agree that tidal volume should be reduced when plateau pressure (Pplat) is as high as 26 cm H2O, rather than waiting until Pplat exceeds 30 or 35 cm H2O, as suggested in some ventilator management guidelines (2). However, our analysis also suggests that there are beneficial effects of tidal volume reduction to 6 ml/kg predicted body weight (PBW) even among patients in whom Pplat is lower than 26 cm H2O before tidal volume reduction. As Dr. Jardin has implied, patients with Pplat of 10 to 18 cm H2O on Day 1 of our trial (segment 1 in Dr. Jardin's letter) had relatively mild reductions in respiratory system compliance. However, more than half (57%) of the patients in this segment had PaO2/FIO2 ratios of 200 or less (acute respiratory distress syndrome [ARDS]), and the mortality of the patients in this segment was 22%. Most of these patients were randomized to the lower tidal volume strategy. Had they received higher tidal volumes their Pplat would have been higher, and we are concerned that their mortality would also have been higher. This is suggested by Quartile 1 in Figure 2 of our article (1).
In their letters, Drs. Jardin, Shiu, and Rosen suggested that Pplat between 18 and 26 (or 28) cm H2O is "safe" because the slope of the relationship of mortality versus Day 1 Pplat (our Figure 1) in this range is not as steep as in the segments of the relationship at lower and higher Pplat. However, the slope of this segment of the relationship is clearly positive ( Our analysis should not be interpreted to mean that tidal volumes should be reduced to very low levels to achieve very low Pplat. We recommend use of the ARDS Network lower tidal volume strategy, in which the tidal volume goal is 6 ml/kg PBW as long as Pplat is 30 cm H2O or less (3). This is not a "one size fits all" approach. In some patients who experience severe dyspnea with tidal volume of 6 ml/kg, the protocol allows increases in tidal volume to 7 to 8 ml/kg PBW. In patients with severe acidosis, the protocol allows increases in tidal volume, even if Pplat then exceeds 30 cm H2O. In some patients whose Pplat exceeds 30 cm H2O with tidal volumes of 6 ml/kg, the protocol recommends tidal volume reduction to 5 or 4 ml/kg. Better and more patient-specific goals for tidal volume and Pplat may be defined in the future with additional knowledge from focused clinical studies.
Johns Hopkins University, Baltimore, Maryland
Massachusetts General Hospital, Boston, Massachusetts FOOTNOTES Conflict of Interest Statement: None of the authors have a financial relationship with a commercial entity that has an interest in the subject of this manuscript REFERENCES
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0.5% mortality/cm H2O Pplat). In addition, this segment represents the greatest density of patients, which increases our confidence in the relationship as depicted between Pplat of 18 and 28 cm H2O. We therefore caution against establishing 26 (or 28) cm H2O as a new safe upper limit of Pplat, especially when mortality continues to decrease at even lower Pplat (< 18 cm H2O).