Effects of Halothane and Enflurane on Right Ventricular Performance in Hearts of Dogs Anesthetized with Pentobarbital Sodium

The effects of enflurane and halothane on contractile force of the right ventricle were compared using the Walton-Brodie strain gage arch and pulmonary artery catheter data in dogs anesthetized with pentobarbital. Twenty mongrel dogs were studied to determine the effects of the two anesthetics on contractile force during a 30-minute exposure to four approximate multiples of MAC: 0.75, 1.0, 1.25, and 2.0, and during a 2-h exposure to 1.0 MAC of each agent. Both anesthetics caused a dose-dependent reduction in contractile force, cardiac output, and mean arterial blood pressure. Enflurane caused greater depression of all variables at all concentrations tested. After a 30-min exposure to 0.75, 1.0, 1.25, and 2.0 MAC, halothane depressed contractile force 33.9%, 37.9%, 46.1%, and 73.4%, respectively, and enflurane depressed contractile force 48.4%, 53.5%, 66.6%, and 81.3%, respectively. The depression produced by enflurane at 1.0 and 1.25 MAC was significantly greater (P less than 0.05) than the depression produced by halothane at equal MAC. The reduction of cardiac output by enflurane at 1.25 and 2.0 MAC was significantly greater than that observed with halothane (P less than 0.05). The decrease in mean blood pressure produced by enflurane was significantly greater (P less than 0.05) than the decrease produced by halothane at 1.0, 1.25, and 2.0 MAC. No significant differences between groups were found in temperature, arterial PCO2, PO2, pH, or hematocrit levels. No diminution of the differences in effect on contractility between the two agents was observed when the exposure period was lengthened to two hours at 1.0 MAC.