Positive end-expiratory pressure (PEEP) ventilation. A review of mechanisms and actions.

In situations characterized by a substantial decrease in lung compliance and a large alveolar-arterial oxygen tension gradient, positive end-expiratory pressure (PEEP) ventilation is often effective in enhancing arterial oxygen content. It may have a variable effect on cardiac output based in part on the level of end-expiratory pressure, the state of intravascular volume, and the pathophysiology of the underlying pulmonary abnormality. It is most beneficial in conditions manifesting diminished lung compliance. Evidence is clear that PEEP may decrease expiratory shunting by maintaining alveolar patency, thereby increasing functional residual capacity. It may not prevent and may actually favor accumulation of interstitial lung water. Commonly employed levels of PEEP result in a 7% incidence of pneumothorax. The most advantageous level of PEEP is variable and is determined by sequential monitoring of multiple physiologic indexes.