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In acute respiratory distress syndrome (ARDS), the aerated and nondependent ventral lung is the most susceptible to ventilatorinduced lung injury (1–6). When positive pressure successfully recruits atelectatic dorsal lung, it is subsequently maintained open by positive end-expiratory pressure (PEEP); tidal recruitment is then diminished (7), and susceptibility of the ventral lung to inspiratory injury is less (6).

Ventilation using excessive PEEP, however, can also overinflate the aerated lung (1, 8) and worsen lung injury. A recent randomized clinical trial in ARDS (9) reported that a strategy combining lung recruitment and higher PEEP based on respiratory system compliance (Crs) increased barotrauma and mortality. A priority for clinicians should be to avoid unnecessarily high PEEP and to find a balance between its positive (ie, decreased dependent atelectasis) and negative (ie, nondependent overinflation) effects.