© 2006 American Thoracic Society
Tidal Volume Reduction in Patients with Acute Lung Injury When Plateau Pressures Are Not HighTo the Editor:In their recent article, Hager and colleagues have reported that a systematic reduction in tidal volume might be beneficial in patients with acute lung injury and acute respiratory distress syndrome (ALI/ARDS), even when plateau pressures are not high (1). They conclude that the commonly held view that inspiratory plateau pressures of 30 to 35 cm H2O are safe is not supported by the available data that they have examined. To be sure, a plateau pressure of 30 to 35 cm H2O is not safe, because it is actually high! In addition, there is a large difference between 35 and 30 cm H2O: 5 cm H2O. This difference is crucial, because plateau pressure in a mechanically ventilated patient is the major determinant of airway distending pressure. As a first consequence, an additional distending pressure of 5 cm H2O will produce an additional stress of the same magnitude on the undamaged areas of the lungs, which are markedly reduced in size in a patient with ARDS (2). As a second consequence, increased distending pressure will markedly impair right ventricular ejection. More than 14 years ago, Whittenberger and coworkers demonstrated in an experimental study in dogs that an increase in transpulmonary pressure from 25 to 30 cm H2O produced an approximately 80% increase in pulmonary vascular resistance (3). Thus, 35 cm H2O, in patients with ARDS, is certainly not a low and safe plateau pressure. Is there a safe plateau pressure in patients with ARDS? I think that Figure 1 in the article by Hager and coworkers begins to answer this question (1). The curve shown in this figure is composed of three segments: a first ascending part, where plateau pressures are between 10 and 18 cm H2O; a second horizontal part, where plateau pressures are between 18 and 26 cm H2O; and finally, a third ascending part, where plateau pressures are above 26 cm H2O. My own interpretation is as follows. The first part can be interpreted as concerning essentially patients with ALI, because a plateau pressure below 18 cm H2O in a patient ventilated with a moderate positive end-expiratory pressure suggests a relatively preserved compliance. The second part probably illustrates a range of safe plateau pressures, between 18 and 26 cm H2O, with no change in mortality in this range in patients with ARDS. More importantly, the third part illustrates that a plateau pressure above 26 cm H2O is harmful, and fully justifies a tidal volume reduction. But this does not mean that the same tidal volume should be applied to all patients (4). I am deeply convinced that applying the recommendations of Hager and coworkers (1), and keeping the plateau pressure below 26 cm H2O in all cases, would help to improve the prognosis of ARDS.
University Hospital Ambroise Paré, Boulogne, France FOOTNOTES Conflict of Interest Statement: F.J. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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