Prone position in the acute respiratory distress syndrome

Since the description of acute respiratory distress syndrome (ARDS) in 1967 (1), mechanical ventilation has been the mainstay therapy of support to these patients. Furthermore, mechanical ventilation has been shown to result in lung injury; thus therapeutic strategies focused on preventing this injury have been shown to significantly decrease mortality (2). It was almost 10 years after the clinical description of ARDS that Piehl and Brown (3) first described the benefit of positional changes to improve arterial oxygenation in five patients with acute respiratory failure. Douglas et al. (4) confirmed these data in a more extensive study and also described significant improvement in arterial oxygenation in most, but not all, patients who were placed in the prone position. Possible mechanisms to explain the improvement of gas exchange during the prone position included a redistribution of blood flow and/or ventilation, an increase in lung functional and residual capacities, and changes in intrapulmonary pressure gradients. These two studies were based on the theoretical work by Bryan (5), who advocated the prone position in mechanically ventilated patients in order to improve regional inflation of dorsal portions of the lung. Over the last 20 years, there have been extensive reports on the pathophysiology of prone ventilation as well as the clinical application in acute lung injury (ALI) and ARDS.