Patients with acute respiratory distress syndrome mechanically ventilated in prone position

Animal experiments and human studies have shown better oxygenation in mechanically ventilated patients with ARDS when the patient is situated in the prone position. In contradiction to former theories of a gravitational gradient of lung perfusion, a number of investigators have found that lung perfusion is preferentially distributed to the dorsal lung regions regardless of body position. The basal atelectasis and oedema in ARDS are resolved and only partly distributed anteriorly in the prone position, and these areas are thereby better ventilated. The combination of better ventilation and unchanged perfusion improves the ventilation/perfusion ratio and decreases the shunt in the prone position. In two cases of prone position in mechanically ventilated patients the PaO2/FiO2 ratio increased from 7.5 to 14.3 and from 8.8 to 19.8 after one hour in the prone position, and some of the improvement was permanent. Prone position has only minor side effects and is recommended as the first choice amongst adjunct therapies in mechanical ventilation in patients with ARDS remaining hypoxic in conventional therapy in the supine position.