COMPARISON OF EFFECTS OF SEVOFLURANE NITROUS-OXIDE AND ENFLURANE NITROUS-OXIDE ON MYOCARDIAL-CONTRACTILITY IN HUMANS - LOAD-INDEPENDENT ANDNONINVASIVE ASSESSMENT WITH TRANSESOPHAGEAL ECHOCARDIOGRAPHY

Background. Few studies have been reported on the direct depressive ef fects of sevoflurane on myocardial contractility in humans. Direct ass essment of contractile state is possible by examining the slope of lef t ventricular end-systolic wall stress (LVESWS) versus velocity of cir cumferential fiber shortening with heart rate corrected (Vcfc) relatio nship with echocardiography. Using this contractile index, the effects of sevoflurane/nitrous oxide were compared with that of enflurane/nit rous oxide on myocardial contractility in humans. Methods: Twenty-eigh t subjects were studied during either sevoflurane/nitrous oxide or enf lurane/nitrous oxide anesthesia. Systolic, diastolic, and mean arteria l blood pressure, heart rate, and transesophageal echocardiographic da ta were determined at 0.9 MAC and 1.35 MAC of sevoflurane or enflurane , both with 60% N2O, and at 1.6 MAC of sevoflurane with 60% N2O. Furth ermore, another 28 awake subjects were studied with transthoracic echo cardiography to examine the contractile state at awake state, and echo cardiograms, heart rate, and arterial blood pressure were recorded. Re sults: Heart rate did not changed significantly in either group. Enflu rane/nitrous oxide produced significantly greater decrease in arterial blood pressure than did sevoflurane/nitrous oxide. The Vcfc at each a nesthetic dose in both anesthetic groups was significantly less than t hat in the awake subjects group. Sevoflurane/nitrous oxide produced no significant change in Vcfc at 1.5 MAC, whereas enflurane/nitrous oxid e caused significant dose-related decrease in vcfc. Vcfc produced by s evoflurane/nitrous oxide was significantly greater than that produced by enflurane/nitrous oxide. There was no significant difference in LVE SWS (index of afterload) between the groups. With respect to the LVESW S-Vcfc relationship, myocardial contractility was significantly depres sed in both the sevoflurane and the enflurane groups compared to the a wake subjects group. However, myocardial contractility produced by enf lurane/nitrous oxide was significantly less than that by sevoflurane/n itrous oxide at equiMAC concentration. Conclusions: The results of the present study suggest that sevoflurane has fewer depressant effects o n cardiac function than does enflurane.