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

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Abstract
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 2 anesthetics on contractile force during a 30-min exposure to 4 approximate multiples of MAC [minimum anesthetic concentration]: 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 < 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 < 0.05). The decrease in mean blood pressure produced by enflurane was significantly greater (P < 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 [partial pressure of Co2], PO2, pH or hematocrit levels. No diminution of the differences in effect on contractility between the 2 agents was observed when the exposure period was lengthened to 2 h at 1.0 MAC.