Study Objective: To compare the characteristics of the rapid induction of anesthesia in pediatric patients with high concentrations of sevoflurane or halothane, and to determine the ability of anesthesiologists to correctly identify the anesthetic drug when administered in this fashion.

Design: Randomized, prospective, open-label study.

Setting: Academic university hospital

Patients: 78 ASA physical status I and II healthy children scheduled for brief surgical procedures with general anesthesia and medicated with midazolam.

Interventions: Assessments were made by 5 pediatric anesthesiologists and 18 anesthesiology residents. Sevoflurane or halothane was randomly selected for anesthetic induction. The anesthetic circuit was primed with the drug (8% sevoflurane or 4% halothane) in 50% nitrous oxide and oxygen. The anesthesiologists were blinded as to the anesthetics being administered. After completion of anesthetic induction, the anesthesiologists were asked to identify the anesthetic and to assess the quality and speed of induction.

Measurement and Main Results: The pediatric anesthesiologists correctly identified the anesthetic in 55 of 78 assessments (70.5%). This figure is statistically better than what could be achieved by random guessing (p < 0.001). The residents correctly identified the anesthetic in only 46 of 78 assessments (60.0%). Statistically, this figure is no better than what could be achieved by random guessing (p = 0.06). Speed of induction was subjectively felt to be faster with sevoflurane than halothane but there were no differences in actual induction time (sevoflurane group, 3.7 ± 2.7 min; halothane group, 3.7 ± 2.6 min). There were no differences in the quality of induction or the incidence of airway complications. The perceived incidence of tachycardia was significantly higher with sevoflurane than halothane(sevoflurane group, 74%; halothane group 20%).

Conclusion: The induction of anesthesia with high concentrations of either halothane or sevoflurane can be safely accomplished. Pediatric anesthesiologists can differentiate between halothane and sevoflurane when either drug is given in high initial concentrations. The presence of tachycardia may have served as the primary clue in determining which drug was being used.