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

Sevoflurane has a non-pungent odour and provides smooth induction of anaest hesia, In contrast, isoflurane is irritating to the airway when used for in duction, and this may also be evident during emergence from anaesthesia. We measured the end-tidal concentration of anaesthetic that prevented respons e to extubation in 50% of patients (MAC(EX)) in adults receiving either sev oflurane or isoflurane, Airway complications during emergence from anaesthe sia were also noted. We studied 51 adult patients, ASA I, aged 36-59 yr. Pa tients received sevoflurane (n = 29) or isoflurane (n = 22) for elective in traocular surgery. The concentration at which extubation was attempted was determined by a modification of Dixon's up-and-down method. When tracheal e xtubation was accomplished without coughing and gross purposeful muscular m ovements within min after extubation, it was considered a smooth tracheal e xtubation. Patients who developed breath-holding or laryngospasm immediatel y after tracheal extubation were regarded as not having been extubated smoo thly. In addition, patients were observed for respiratory events during the remainder of the emergence period. MAC(EX) values for sevoflurane and isof lurane were 1.07% and 0.83%, respectively. ED95 Values of sevoflurane and i soflurane were 2.04% and 1.19%, respectively, In 12 patients in the isoflur ane group, extubation was smooth but six patients had coughing episodes dur ing the remainder of the emergence period. In contrast, one of 15 patients in the sevoflurane group in whom tracheal extubation was smooth coughed lat er (P = 0.035). Airway obstruction was frequent when tracheal extubation wa s performed at end-tidal concentrations exceeding I MAC(EX) for each anaest hetic.