Effects of enflurane on haemodynamics and oxygen consumption in the dog with special reference to the liver and preportal tissues.

The effects of enflurane anaesthesia on central circulation, total oxygen uptake, splanchnic circulation and splanchnic oxygen uptake were studied in 10 artifically ventilated dogs, basally anaesthetized with thiopental and nitrous oxide. Hepatic arterial, superior mesenteric arterial and portal venous blood flows were measured with electromagnetic flowmetry. Cardiac output was measured by thermodilution. Determinations of oxygen contents were made in arterial, pulmonary arterial, portal venous and hepatic venous blood. The end-tidal enflurane concentration was kept at about 1 MAC (= 2.2%). Arterial blood pressure diminished 54% of control value due to decreases of cardiac output to 65% and of total peripheral vascular resistance to 81% of control values. Hepatic arterial, superior mesenteric arterial and portal venous blood flows decreased to 65-70% of control levels and the corresponding vascular resistances all declined to about 80-85% of control values. Total oxygen uptake decreased, but less than cardiac output, leading to an increased arterio-venous oxygen content difference. Oxygen uptake of the preportal tissues was unchanged and hepatic oxygen uptake was not significantly altered, although there were decreases in hepatic oxygen uptake in some of the individual experiments. It is suggested that the cardiovascular depression following enflurane anaesthesia in the dog was due, to a great extent, to a primary myocardial depression. It is further concluded that the splanchnic blood flows were relatively well preserved, due to decreases in splanchnic vascular resistances, and that hepatic and preportal tissue oxygen consumptions were maintained by increased oxygen extraction.