Portal blood flow in man during graded positive end-expiratory pressure ventilation.

The cardiovascular response to graded PEEP ventilation (5-10 cm H20) was studied peroperatively in patients undergoing cholecystectomy (n = 8) or hepatic tumour surgery (n = 3). Portal blood flow was measured by the continuous thermodilution technique and cardiac output, in a sub-group of the patients, by impedance cardiography. A parallel reduction in cardiac output and portal blood flow was demonstrated in patients undergoing cholecystectomy as the result of the application of PEEP. Thus, ventilation with 5 cm H2O of PEEP elicited a 17% decrease in cardiac output and a 26% decrease in portal blood flow. During 10 cm H2O of PEEP cardiac output decreased by 22% and portal blood flow by 32%. However, there were no significant changes in preportal tissue perfusion pressure by the application of PEEP and preportal vascular resistance increased by 22% and 30%, respectively. This indicates that a vasoconstrictor response, elicited by PEEP, in the preportal tissue is the predominating mechanism for the observed decrease in portal blood flow. Systemic oxygen transport decreased by 214 ml/min during PEEP ventilation, but preportal tissue oxygen utilization was not significantly changed due to a concurrent increase (2.9%; p less than 0.05) in oxygen extraction.