This study aimed to discover the effects of artificial ventilation with positive end-expiratory pressure (PEEP) on cardiac output and hepatic blood flow in ten patients with chronic stable post-anoxic or post-traumatic coma, without any cerebral oedema or any other visceral pathology. This study was carried out at four levels of end-expiratory pressure (0, 5, 12 and 29 cmH2O) and after 24 h of artificial ventilation with a PEEP arbitrarily fixed at 12 cmH2O. Cardiac output was measured by thermodilution and hepatic blood flow by applying Fick's principle on a continuous infusion of indocyanine green with an analysis of suprahepatic venous samples. Hepatic blood flow is given by the amount of indocyanine green infused (0.5 mg.min-1) divided by the difference between arterial and suprahepatic venous indocyanine green concentration. For all levels of PEEP, mean arterial, right atrial, wedge and suprahepatic pressures and hepatosplanchnic resistances were measured. Artificial ventilation with PEEP induced a fall of cardiac output and hepatic blood flow proportional with the increase in PEEP level. The fall in hepatic blood flow began to be statistically significant for a PEEP level of 5 cmH2O (-17%; p less than 0.01) and was maximum for a PEEP of 20 cmH2O (-49.51%; p less than 0.001). There was no linear correlation between cardiac output and hepatic blood flow: the fall in hepatic blood flow was more important than the fall in cardiac output. These changes in hepatic blood flow were accompanied by a significant increase in hepatosplanchnic resistances (p less than 0.01 for PEEP = 12 cmH2O), without any changes in other haemodynamic parameters or biological signs of hepatic disturbance.(ABSTRACT TRUNCATED AT 250 WORDS)