Influence of volatile anesthetics on myocardial contractility in vivo: Desflurane versus isoflurane

Abstract

The direct effects of desflurane on myocardial contractility in vivo have not been characterized. Therefore, the purpose of this investigation was to systematically examine the effects of desflurane on myocardial contractile function and compare these actions to equi-anesthetic concentrations of isoflurane in chronically instrumented dogs. Contractility was evaluated using an established index of inotropic state, the preload recruitable stroke work (PRSW) versus end-diastolic segment length (EDL) relationship. Since autonomic nervous system tone may influence the hemodynamic effects of the volatile anesthetics in vivo, experiments were performed in the presence of pharmacologic blockade of the autonomic nervous system. Two groups of experiments were performed with seven dogs instrumented for measurement of aortic and left ventricular pressure, the maximum rate of increase of left ventricular pressure (dP/dt), subendocardial segment length, coronary blood flow velocity, and cardiac output. After autonomic nervous system blockade, ventricular pressure-segment length loops were generated using preload reduction via partial inferior vena caval occlusion. The PRSW versus EDL relation was calculated from the pressure-length loops. Dogs were then anesthetized with 1.0 or 1.5 MAC desflurane or isoflurane in a random fashion, and measurements were repeated after 30 min of equilibration at each anesthetic concentration. The PRSW versus EDL slope reflected similar changes in contractile state when desflurane or isoflurane was administered (53 ± 4 during control to 26 ± 4 erg·cm-2·10-3·mm-1 at 1.5 MAC desflurane, and 57 ± 5 during control to 31 ± 3 erg·cm-2·10-2·mm-1 at 1.5 MAC isoflurane). In conclusion, desflurane and isoflurane produced equivalent direct decreases in myocardial contractility.