Effects of enflurane and isoflurane on hepatic and renal circulations in chronically instrumented dogs.

Seven dogs were chronically instrumented for measurements of mean aortic blood pressure and cardiac output and for simultaneous measurements of hepatic, portal, and renal blood flows. Each animal was studied on two separate occasions, awake and during 1.2, 1.4, 1.75, and 2.0 MAC isoflurane and enflurane. Both anesthetics induced tachycardia; to a greater degree than isoflurane, enflurane lowered mean aortic blood pressure in a dose-dependent manner (-37, -45, -48, and -62% vs. -19, -25, -41, and -44%, respectively) and cardiac output (-20, -26, -41, and -48% vs. -3, -5, -11, and -15%, respectively). With isoflurane, cardiac output decreased only at 1.75 and 2.0 MAC, and portal blood flow did not change significantly, whereas hepatic arterial blood flow increased at 1.75 and 2 MAC (by 28 and 33%, respectively). With enflurane, no significant changes were recorded in hepatic arterial blood flow, whereas portal blood flow decreased in a dose-dependent manner. Except at 2 MAC, hepatic circulation did not differ between anesthetics. Likewise, neither anesthetic significantly changed renal blood flow, except for enflurane at 2.0 MAC, which was associated with a 35% reduction. Both anesthetics led to similar systemic, hepatic, and renal vasodilations. Our data suggest that high concentrations of enflurane are associated with decreases in portal, total hepatic, and renal blood flows, most likely as a result of an anesthetic-induced cardiac depression.