Prone ventilation in acute respiratory distress syndrome

Prone positioning has been used for many years in patients with acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), with no clear benefit for patient outcome. Meta-analyses have suggested better survival in patients with an arterial oxygen tension (PaO2 )/inspiratory oxygen fraction (FIO2 ) ratio <100 mmHg. A recent randomised controlled trial was performed in ARDS patients after a 12-24 h stabilisation period and severity criteria (PaO2 /FIO2 <150 mmHg at a positive end-expiratory pressure ≥5 cmH2O). This trial has demonstrated a significant reduction in mortality from 32.8% in the supine group to 16% in the prone group (p<0.001). The reasons for this dramatic effect are not clear but probably involves a reduction in ventilator-induced lung injury due to prone positioning, for which there is ample evidence in experimental and clinical studies. The aims of this article are to discuss: the rationale of prone positioning in patients with ALI/ARDS; the evidence of its use based on trial analysis; and the limitations of its use as well as the current place of prone positioning in the management of patients with ALI/ARDS. From the currently available data, prone positioning should be used as a first-line therapy in patients with severe ALI/ARDS.