Haemodynamic responses to isoflurane anaesthesia and hypovolaemia in the dog, and their modification by propranolol.

In six dogs chronically implanted with flow and pressure transducers, equipotent inspired concentrations of halothane and isoflurane were determined as the minimum inspried concentration of each agent which would abolish an individual dog's response to paw clamping. In equipotent concentration, isoflurane (1.2%, SD 0.2%) caused less myocardial depression than halothane (1.0%, SD 0.1%). Dose-response studies were possible up to a mean inspired isoflurane concentration of 3.0%, both before and after propranolol 0.3 mg kg-1, i.v. After propranolol, sensitive indices of myocardial contractility were depressed at all concentrations of isoflurane, indicating a moderate degree of beta-receptor activation by isoflurane. The haemodynamic response to hypovolaemia during isoflurane anaesthesia was not modified by propranolol.