DIRECT COMPARATIVE EFFECTS OF ISOFLURANE AND DESFLURANE IN ISOLATED GUINEA-PIG HEARTS

The aim of this study was to test if myocardial and coronary vascular effects of desflurane and isoflurane were similar in the isolated heart. The cardiac effects of these anesthetics were examined in 12 guinea pig hearts perfused in a retrograde manner. Spontaneous heart rate, atrioventricular (AV) conduction time, systolic left ventricular pressure, and coronary flow were measured. To differentiate direct vasodilatory effects of these anesthetics from an indirect metabolic effect due to autoregulation of coronary flow, O2 delivery (D(O2)), myocardial O2 consumption (MV(O2)) and percent O2 extraction were also monitored. Isoflurane and desflurane were injected directly into sealed bottles containing oxygenated perfusate solution. Each heart was perfused randomly with these anesthetics. Anesthetic concentrations in the perfusate were 0.28 +/- 0.02 and 0.52 +/- 0.02 mM for isoflurane and 0.59 +/- 0.01 and 1.02 +/- 0.09 mM for desflurane (mean +/- standard error of the mean). Calculated vapor concentrations were 1.3 and 2.5 vol % for isoflurane and 6.8 and 11.8 vol % for desflurane which correspond to approximately 1 and 2 MAC in vivo. Each anesthetic similarly decreased heart rate and prolonged AV conduction time in a concentration-dependent manner. Left ventricular pressure (control 93 +/- 4 mmHg) decreased by 11 +/- 1% and 24 +/- 2% with isoflurane and by 15 +/- 1% and 30 +/- 2% with desflurane. The decreases in heart rate and pressure were accompanied by decreases in MV(O2) of 12 +/- 2% and 30 +/- 3% with isoflurane and of 19 +/- 3% and 40 +/- 4% with desflurane from a control of 57 +/- 2-mu-l.g-1.min-1. Although MV(O2) decreased, coronary flow (control 5.7 +/- 0.2 ml.g-1.min-1) increased submaximally by 16 +/- 2% and 30 +/- 4% with isoflurane and by 10 +/- 2% and 19 +/- 3% with desflurane. These changes in left ventricular pressure, MV(O2), and coronary flow were significantly different between isoflurane and desflurane at both anesthetic levels. D(O2) increased proportionally with coronary flow. The differences in D(O2) and MV(O2) were proportional so that the D(O2)/MV(O2) ratios, as well as percent O2 extraction, were not different between isoflurane and desflurane. This study shows that desflurane, like isoflurane, is a direct myocardial depressant in the isolated heart. Although desflurane produced a slightly greater negative inotropic effect than isoflurane, both anesthetics had similar coronary vasodilatory effects on the basis of similar increases in the ratio of D(O2) to MV(O2).