What is the optimal duration of ventilation in the prone position in acute lung injury and acute respiratory distress syndrome?

OBJECTIVE: To evaluate the effects of prone ventilation on respiratory parameters and extravascular lung water (EVLW) in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) in order to characterise the optimal duration of ventilation in the prone position. DESIGN: Prospective, observational study. SETTING: Nine-bed general intensive care unit. PATIENTS: Eleven patients with refractory hypoxaemia due to ALI/ARDS were prospectively investigated during 12 consecutive episodes of prone ventilation. INTERVENTIONS: Ventilation in the prone position for 18 h. MEASUREMENTS AND MAIN RESULTS: Measurements were obtained supine and after 1, 2, 6, 12 and 18 h in the prone position and 1 h after returning supine. There was a progressive improvement in PaO(2)/fraction of inspired oxygen (FIO(2)) ratio which reached significance after 12 h [121 (81-151) to 258 (187-329) torr; p