Positive end expiratory pressure (PEEP) during ventilation improves arterial oxygenation by recruiting alveoli, but it may cause circulatory depression and increase airway pressure and lung volumes resulting in ventilator induced lung injury from overdistension.

In acute lung injury and acute respiratory distress syndrome (ARDS), mechanical ventilation is critical for the survival of the majority of patients. Most patients with acute lung injury and ARDS have been treated with PEEP values of 5–12 cm H₂O. In this study, 549 patients with acute lung injury and ARDS were randomised to receive either high PEEP (13.2 (3.5) cm H₂O) or lower PEEP (8.3 (3.2) cm H₂O). All patients received a tidal volume goal of 6 ml/kg predicted body weight and an inspiratory plateau pressure of 30 cm H₂O or less. Blood samples reflecting mechanisms of lung inflammation and injury (plasma interleukin-6, surfactant protein D, and intercellular adhesion molecule 1) were obtained before randomisation (day 0) and on day 3. The mortality rate from any cause was 24.9% in the lower PEEP group and 27.5% in the higher PEEP group. There were no changes in plasma levels of biological markers of inflammation and lung injury in either group.

The authors conclude that, in patients with acute lung injury and ARDS who receive mechanical ventilation with a tidal volume goal of 6 ml/kg predicted body weight and an end inspiratory plateau pressure limit of 30 cm H₂O, clinical outcomes are similar whether lower or higher PEEP levels are used.