Rapid inhalational induction of anaesthesia with isoflurane or halothane in humidified oxygen

This study was designed to determine the relative speeds of induction and complication rates using either halothane or isoflurane for rapid inhalational induction of anaesthesia. Forty ASA physical status 1 and 2, unpremedicated patients presenting for day-care dental surgery received a rapid inhalational induction (RII) with either halothane 3.5% or isoflurane 5% in humidified oxygen. The carrier gas was humidified in order to limit airway irritation caused by the pungency of the volatile agents. Isoflurane produced a faster induction than halothane-121(50) (SD) sec vs 176(36) sec (P less than 0.01). Complication rates during induction (coughing, secretions, excessive movement and abandoned inductions) were similar for the two groups. The majority of patients in both the isoflurane group (17/20) and the halothane group (14/20) found the technique of RII to be acceptable. The incidences of headache, nausea and vomiting were low and not significantly different for the two groups. Isoflurane 5% in humidified oxygen is as acceptable for RII as halothane 3.5% and has a similar complication rate. Isoflurane may be used for RII in cases where it is deemed necessary to avoid halothane, or when a more rapid inhalational induction is required than is possible with halothane. The technique of RII with either agent in unpremedicated patients is well suited to day-care anesthesia.