Sevoflurane is characterized by the lack of an unpleasant odor, airway irritation and its low blood/gas partition coefficient (0.68), which provides rapid and smooth induction. Inhaled induction with sevoflurane is commonly used in pediatric patients, but not in adult patients. This study was designed to investigate the time to completion of LMA insertion and end-tidal sevoflurane concentration during induction with sevoflurane 8% and N2O 50%, after midazolam administration, in adults.

Twenty eight patients, aged 20(-60) years, were administered intravenous midazolam 30 µg/kg and after one minute, sevoflurane 8% and N2O 50% were inhaled with tidal-volume breathing. One minute after loss of consciousness, jaw thrust and mouth opening were checked and an LMA was inserted. The end-tidal concentration of sevoflurane, and the times to loss of consciousness and completion of insertion were recorded. The mean arterial pressure and heart rate were also recorded.

From initiation of sevoflurane and N2O inhalation, it took 48 ± 14 seconds until loss of consciousness, and 143 ± 19 seconds until the completion of LMA insertion. The end-tidal sevoflurane concentration was 4.1 ± 0.6% at loss of consciousness, 5.0 ± 0.7% at one min after loss of consciousness, and 4.1 ± 0.5% after LMA insertion. In all patients LMA insertion was successful and satisfactory. After LMA insertion, compared to baseline, the mean arterial pressure was reduced and the heart rate increased.

After small-dose of midazolam, inhaled induction with sevoflurane 8% and N2O 50% allowed successful and satisfactory LMA insertion in adults.