End-tidal sevoflurane concentration for tracheal extubation (MACEX) in adults: comparison with isoflurane

Sevoflurane has a non-pungent odour and provides smooth induction of anaesthesia. In contrast, isoflurane is irritating to the airway when used for induction, and this may also be evident during emergence from anaesthesia. We measured the end-tidal concentration of anaesthetic that prevented response to extubation in 50% of patients (MACEX) in adults receiving either sevoflurane or isoflurane. Airway complications during emergence from anaesthesia were also noted. We studied 51 adult patients, ASA 1, aged 36-59 yr. Patients received sevoflurane (n = 29) or isoflurane (n = 22) for elective intraocular surgery. The concentration at which extubation was attempted was determined by a modification of Dixon's up-and-down method. When tracheal extubation was accomplished without coughing and gross purposeful muscular movements within 1 min after extubation, it was considered a smooth tracheal extubation. Patients who developed breath-holding or laryngospasm immediately after tracheal extubation were regarded as not having been extubated smoothly. In addition, patients were observed for respiratory events during the remainder of the emergence period. MACEX values for sevoflurane and isoflurane were 1.07% and 0.83%, respectively. ED95 values of sevoflurane and isoflurane were 2.04% and 1.19%, respectively. In 12 patients in the isoflurane group, extubation was smooth but six patients had coughing episodes during the remainder of the emergence period. In contrast, one of 15 patients in the sevoflurane group in whom tracheal extubation was smooth coughed later (P = 0.035). Airway obstruction was frequent when tracheal extubation was performed at end-tidal concentrations exceeding 1 MACEX for each anaesthetic.