Inaccuracy of Pulmonary Capillary Wedge Pressure when Compared to Left Atrial Pressure in the Early Postsurgical Period

Simultaneous measurements of pulmonary capillary wedge pressure (PCWP) and left atrial pressure (LAP) were obtained before and after cardiopulmonary bypass and for a period of 16 hours postoperatively in 20 consecutive patients undergoing electric cardiac operations. In contrast to several previous reports that PCWP accurately reflects left-sided hemodynamics, we found that the PCWP significantly exceeded the LAP in the early postbypass period and was most significantly in error at 4, 8, and 12 hours after operation (p less than .02) (95% confidence limit). The magnitude of this discrepancy differed in individual patients; however, it was consistent for each patient for the time period studied and independent of the procedure performed. The disparity between PCWP and LAP may be due to an increase in lung interstitial water as a result of hemodilution, or it may be related to the differing effects of afterload reducing agents on the pulmonary versus the systemic circulation. We conclude from these data that LAP more accurately reflects left ventricular filling and performance in the early postoperative period and should be used instead of PCWP to monitor the hemodynamics of postsurgical patients.