The effect of vascular volume on positive end-expiratory pressure-induced cardiac output depression and wedge-left atrial pressure discrepancy.

Positive end-expiratory pressure (PEEP) is effective in improving arterial oxygenation and decreasing intrapulmonary shunt in patients with the adult respiratory distress syndrome [9, 121. PEEP can also cause a significant reduction in cardiac output [6, 8, 13, 15]anddecreaseinoxygendelivery[12]. The decrease in cardiac output may be due to impaired venous return [ 1, 7, 141, pulmonary vascular compression [5, 6, 121, or left ventricular dysfunction [8, 131 and may be reversed by acute volume expansion [14, 171. When cardiac output falls with PEEP, pulmonary capillary wedge pressure may not accurately reflect left atria1 pressure [5, 8, 121 and, thus, is a poor monitor of volume requirements in patients. Six baboons were studied to determine more accurately the effect of PEEP on cardiac output and the relation between wedge and left atria1 pressure under conditions of acute and chronic volume expansion.