Effect of isoflurane on the canine hepatic circulation and hepatic oxygen balance

We have studied the effects of increasing concentrations of isoflurane (1%, 1.5% and 2%) on the hepatic circulation and the oxygen supply and demand of the liver in six barbiturate-anaesthetized greyhounds. Following laparotomy, the hepatic arterial and portal venous blood flows were measured continuously using electromagnetic flow probes, and mean arterial pressure and cardiac output were measured as appropriate. Cardiac output was maintained while mean arterial pressure and systemic vascular resistance decreased in a dose dependent manner. Hepatic arterial and total liver blood flows and oxygen supplies decreased significantly at all isoflurane concentrations. Portal venous blood flow and portal venous oxygen supply did not decrease significantly until the concentration of isoflurane was increased to 2% and 1.5%, respectively. Hepatic oxygen consumption was reduced with 2% isoflurane (P less than 0.05), but this was insufficient to offset the reduction in hepatic oxygen supply and resulted in an increased extraction of oxygen by the liver.