Humorally mediated alterations in cardiac performance as a consequence of positive end-expiratory pressure

Two experimental designs were used to study the mechanism of the decreased cardiac output associated with the use of positive end-expiratory pressure (PEEP). In the first study of nine dogs the application of 15 cm H2O PEEP led to a decrease in cardiac output (CO) from 2.68 +/- 1.05 to 2.01 +/- 1.26 liters/min (+/- SD) (p less than 0.05) concomitant with an increase in transmural central venous pressure of 5.2 +/- 0.9 to 8.4 +/- 2.7 mm Hg (p less than 0.05) and a slight increase in transmural left atrial pressure of 6.8 +/- 3.3 to 7.3 +/- 3.6 mm Hg (p less than 0.1). These data are consistent with altered ventricular performance. In a second study nine pairs of dogs were cross-circulated. Application of 15 cm H2O PEEP to one member of the experimental pair led to a decrease in the CO of the other member from 2.71 +/- 0.98 to 2.21 +/- 0.81 liters/min (p less than 0.001). This decrease returned toward baseline with the removal of PEEP (p less than 0.02). Results indicate that one mechanism whereby PEEP reduces the cardiac output is through the action of a humoral agent.