A peek at PEEP in patients with AIDS.

PEEP was described to improve oxygenation in ventilated patients with ARDS in 1967,1 although the mechanism of action was not clear. The potential benefits of lung volume recruitment maneuvers became apparent from results of a randomized controlled trial of mechanical ventilation of patients with ARDS in 1998.2 Since that time there has been a proliferation of literature in the area of lung volume recruitment.3 It has become recognized that PEEP largely acts to maintain the recruitment benefit achieved by tidal ventilation. More complex maneuvers have been studied over the past decade to open atelectatic lung units, such as sustained inflation,4 incremental PEEP,5 intermittent higher volume ventilation or “sighs,”6 and highfrequency oscillation.7 In this context, the physiological study by Anjos et al published in this issue of RESPIRATORY CARE,8 evaluating the oxygenation benefits of PEEP, is somewhat anachronistic (although carried out in 2000), but addresses some important physiological principles and demonstrates the complexities of lung volume physiology.