Acute Respiratory Distress Syndrome

To the Editor: In their review of the acute respiratory distress syndrome (ARDS) (Aug. 10 issue), 1 Thompson et al. recommend that patients be placed in the prone position when the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (Pa o 2 :F io 2 ) is less than 120 mm Hg. However, the guidelines for the mechanical ventilation of patients with ARDS 2 recommend this strategy for patients with severe ARDS, which the guidelines define as a Pa o 2 :F io 2 of less than 100 mm Hg. Furthermore, one of the inclusion criteria for a trial that showed a decrease in mortality with this . . .