Low vs high positive end-expiratory pressure in the ventilatory management of acute lung injury

Positive end-expiratory pressure (PEEP) has become an essential component of the care of many critically ill patients who require ventilatory support. The application of PEEP is expected to improve lung mechanics and gas exchange as it recruits lung volume. In the last 3 decades, research of the effects of PEEP in animal models of lung injury and in patients with acute respiratory failure has produced a plethora of information. Support for the use of PEEP comes from historical comparisons and a few randomized controlled studies. Although the data from those animal studies and clinical trials could be seen as very convincing, there are insufficient data to propose an universal approach for the use of PEEP in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). In this article I will review the basic mechanisms of PEEP and the current knowledge of the effects of PEEP on the evolution and outcome of ALI/ARDS.