Neuromuscular Effects of Atracurlum during Halothane—Nitrous Oxide and Enflurane—Nitrous Oxide Anesthesia in Humans

Abstract

To compare the effect of halothane and enflurane on an atracurium-induced neuromuscular blockade, the authors studied 40 patients during elective surgery. During 1.25 MAC [minimum anesthetic concentration] enflurane-nitrous oxide (n = 20) or halothane-nitrous oxide (n = 20) (MAC value includes contribution from 60% nitrous oxide), the doses depressing twitch tension 50% (ED50s) [median effective dose] for atracurium were 70 and 77 .mu.g/kg, respectively. The difference was not significant. Time from injection to peak effect did not differ between groups. However, the duration of action of atracurium (expressed as duration50 or the duration of a 50% blockade) was longer during enflurane-nitrous oxide anesthesia (34.2 min) than during halothane-nitrous oxide anesthesia (25.5 min) (P < 0.05). The potency of atracurium does not differ during halothane-nitrous oxide and enflurane-nitrous oxide anesthesia. Combining the results of this study with a previous study (atracurium ED50 = 68 .mu.g/kg and 83 .mu.g/kg during isoflurane-nitrous oxide and fentanyl-nitrous oxide anesthesia respectively), the potency of atracurium does not differ by more than 20% among the 4 anesthetic techniques studied. The background anesthetic appears to have less effect on an atracurium-induced neuromuscular blockade than on 1 produced by other longer-acting nondepolarizing muscle relaxants (e.g., pancuronium and d-tubocurarine).