ED50 of desflurane for laryngeal mask airway removal in anaesthetised adults.

Previous estimates for the end-tidal concentration of desflurane that allows removal of the laryngeal mask airway in 50% of anaesthetised adults (ED50) have ranged from 2.1% to 5.3%. To assess which value is correct, we studied 32 female patients (aged 30-50 years) undergoing intracavity caesium implants for cervical carcinoma under general anaesthesia. Anaesthesia was induced with propofol 2-3 mg.kg(-1) and maintained with desflurane in a 50% nitrous oxide-oxygen mixture. At the end of surgery, a predetermined target end-tidal desflurane concentration (starting at 4%) was maintained for 10 min using Dixon's up-down method and the laryngeal mask airway was removed. The target end-tidal concentration in the next patient was increased or decreased by 0.5% depending upon the response of the previous patient. Removal of the laryngeal mask airway without coughing, clenching, biting, movement or any adverse airway event during or within 1 min after removal was considered to be successful. We found that the laryngeal mask airway can be successfully removed in 50% (ED50) and 95% (ED95) of the anaesthetised adults at end-tidal desflurane concentrations of 2.4% (95% CI 1.3-2.9) and 3.8% (3.1-9.6), respectively.