Comparison of halothane and isoflurane for rapid anesthetic induction

To study the hypothesis that isoflurane will induce anesthesia faster than halothane when given by a single vital capacity breath technique, we studied 20 ASA I and II adults who breathed approximately 4.5 MAC equivalents of either vapor. The patients, randomly assigned to receive either agent, were fully preoxygenated and monitored for cardiovascular, respiratory, and EEG parameters. All subjects were premedicated with 5 micrograms/kg fentanyl IV 5 min before induction. Time to loss of consciousness was significantly longer with halothane than with isoflurane (86 +/- 4 vs 38 +/- 2 sec, respectively) although there were no clinically remarkable differences in cardiovascular or respiratory variables. Patients given halothane had a greater excitatory phase on EEG, whereas those given isoflurane had low frequency predominance. Overall rapid inhalation induction was well-received by all patients and was significantly faster with isoflurane.