ABSTRACT
One hundred seventeen adult surgical patients were studied to compare neuromuscular and cardiovascular effects of mivacurium chloride during nitrous oxide-narcotic [BAL, n = 45] nitrous oxide-halothane [HAL, n = 27] and nitrous oxide-isoflurane [ISF, n = 45] anesthesia. Anesthesia was maintained with nitrous oxide [60%-70%] and oxygen [30%-40%] with end-tidal concentrations of halothane or isoflurane to yield a total MAC of approximately 1.25, or with supplemental fentanyl and thiopental as clinically indicated. Twitch response of the adductor pollicis muscle was elicited by supramaximal square wave pulses of 0.2 msec duration at a frequency of 0.15 Hz [Grass S44 stimulator] to the ulnar nerve and quantitated by a Grass FT10 transducer. Nine patients in each of the HAL and 1SF groups received one of four doses of mivacurium [0.03, 0.05, 0.10 or 0.15 mg/kg]. Ninety patients in the balanced anesthesia group received one of seven doses of mivacurium [0.03, 0.04, 0.05, 0.08, 0.15, 0.20, 0.25 mg / kg]. The ED50, ED75 and ED95 of mivacurium in each group were estimated from linear regression plots of log dose versus probit of maximum percentage depression of twitch height. The ED50, ED75 and ED95 for halothane and isoflurane are 0.040, 0.053 and 0.081 and 0.037, 0.043 and 0.053, respectively. The ED50, ED75, and ED95 for the balanced group are 0.039, 0.050, and 0.073 mg/kg respectively. There was no significant difference between the slopes of the HAL and BAL inhalation anesthetic dose-response curves. The slope of the ISF group was significantly than the slope of the BAL group. Intercepts of the HAL and BAL curves were not different. The isoflurane curve's intercept was significantly less than the other groups' intercepts, lying above the halothane curve, but below the BAL curve. For the 0.05 mg/kg dose, maximum block was greater in the 1SF group [89.1 +/- 2.7%, n = 9] than in the HAL [70.3 +/- 7.6%, n = 9] or BAL [67.7 +/- 6.4%, n = 9] groups. At higher doses of mivacurium, isoflurane produces a greater potentiation of neuromuscular block than halothane or balanced anesthesia. There were no significant cardiovascular changes seen in any group following mivacurium doses up to 0.15 mg/kg [approximately 2xED95]