Comparison of cardiac effects of enflurane, isoflurane, and halothane in the dog heart-lung preparation.

Minimum alveolar concentration (MAC) was determined in intact dogs (N = 10 for each anesthetic) to be 2.12 +/- 0.04 vol% for enflurane (ENF), 1.28 +/- 0.04 vol% for isoflurane (ISO), and 0.94 +/- 0.03 vol% for halothane (HAL). Then, the direct cardiac effects of these three anesthetics were studied at 0.36, 0.6, 1.0, and 1.2 MAC in the dog heart-lung preparation (HLP): an in situ whole heart preparation devoid of major extracardiac influences and reflex control. All three agents produced concentration-dependent decreases in heart rate (HR) that became significantly different from control at 0.6 MAC. HAL and ISO reduced +dP/dtmax by the same degree at all MAC levels, becoming statistically significant at 0.6 MAC, while a significant reduction in +dP/dtmax for ENF occurred first at 1.0 MAC. Marked increases in left atrial pressure (LAP) were observed at 1.0 MAC for all anesthetics and the first significant depression of systemic output (SO) occurred at 1.0 MAC. Each agent produced significant shifts of the left ventricular function curves (LVFC) to the right with each consecutive MAC fraction. Marked reductions in the slope of the LVFC were first observed at 1.0 MAC, and this change in slope was more pronounced with ENF. At 1.2 MAC, ENF seemed to produce a more severe cardiodepression than HAL or ISO, as suggested by a greater incidence of cardiac failure; however, this was not statistically significant. In general, the data suggest that at MAC fractions up to 0.6, ENF is less cardiodepressant than ISO or HAL, but that ENF has a tendency to be more depressant than HAL or ISO at concentrations higher than 1.0 MAC.