Criteria for Optimum PEEP

Abstract

The use of positive end-expiratory pressure (PEEP) in selected patients has demonstrated its ability to resolve intrapulmonary shunt. Several recently published studies have attempted to characterize the "optimal" level of PEEP as that which coincides with the lowest measured intrapulmonary shunt. However, because shunt measurements reflect the performance of the lungs without revealing simultaneous changes in cardiac function, such an approach may fail to indicate the optimum level of PEEP. On the other hand, physiologic indices that allow the clinician to assess the separate, and often competing, effects of PEEP on cardiac and ventilatory function are clearly superior when one is attempting to identify the optimal PEEP level. Of the composite measures currently available, the direct measurement of mixed venous oxygen tension is the most definitive. For certain patients in whom invasive techniques must be deferred, monitoring of static total compliance may offer an alternative. In any event, progressive increases in PEEP to a level that coincides with the minimum degree of intra- pulmonary shunting represent aggressive pursuit of a questionable goal. The increased risk of pulmonary barotrauma that attends the institution of extremely high PEEP levels suggests that overzealous use of this modality might well be considered a triumph of technique over judgement.