Pulmonary artery occlusion pressure is not accurate immediately after cardiopulmonary bypass

Elevated pulmonary vascular resistance (PVR), differential cardiac dynamics, and increased lung water following cardiopulmonary bypass (CPB) have been proposed as limitations to the accuracy of the pulmonary artery occlusion pressure (PAOP) in estimating left ventricular preload. A prospective study of 22 patients undergoing elective myocardial revascularization is described wherein PAOP was compared with directly measured left atrial pressure (LAP). The reliability of PAOP to estimate LAP in the hour immediately following CPB and at 1, 4, 8, and 12 hours post-CPB was examined with repeated measures analysis of variance. Relationships between the PAOP-LAP difference and PVR, core temperature, arterial CO2 tension, and right and left ventricular stroke work indices (RVSWI, LVSWI) were tested by linear regression analysis. There was greater variability in measurements at 15, 30, and 45 minutes immediately after CPB, demonstrated by a pooled correlation coefficient of 0.73 versus 0.90 in the postoperative period. The degree of discrepancy between PAOP and LAP lessened with time. There was no determinable relationship of the PAOP-LAP gradient to PVR, level of PCO2, temperature, RVSWI, or LVSWI. Potential sources of discrepancy include airway pressure effects, position of the measuring catheters, positive end-expiratory pressure, infusion of protamine sulfate, extremes of pulmonary artery pressures, and effects of an open pericardium.(ABSTRACT TRUNCATED AT 250 WORDS)