Increased pulmonary artery diastolic-pulmonary wedge pressure gradient after cardiopulmonary bypass

In 29 patients undergoing elective coronary artery bypass grafting, the diastolic pulmonary arterial pressure-pulmonary capillary wedge pressure gradient (DPAP-PCWP) and related haemodynamic parameters were determined before and after induction of anaesthesia, immediately after cardiopulmonary bypass (CPB) and one and three hours after CPB. The DPAP-PCWP gradient remained unchanged after induction of anaesthesia but was significantly increased after CPB. A gradient of 5 mmHg or greater was observed in 16 patients after CPB, whereas none of the patients showed such a gradient before CPB. A significant correlation was found between the change in DPAP-PCWP and the change in pulmonary vascular resistance (PVR). It is concluded that DPAP should not be used as a substitute of PCWP in the early postbypass period without frequent confirmation of the presence of the normal small DPAP-PCWP gradient. Since an increase of PVR may impair right ventricular ejection, we recommend the routine measurement of DPAP-PCWP gradient in the postbypass period.