Desflurane requirements for laryngeal mask airway insertion during inhalation induction

We hypothesized that the simultaneous use of low concentrations (<6%) of desflurane, nitrous oxide (N(2)O), and fentanyl would allow a laryngeal mask airway (LMA) to be inserted safely with inhalation induction of desflurane, even in nonparalyzed patients. This prospective, observational study was performed to determine the 50% effective concentration (EC(50)) of desflurane for LMA insertion in such patients.

Twenty-two adult patients undergoing ambulatory surgical procedures under general anesthesia using an LMA were included in the study. Fentanyl was administered intravenously at 1.5 microg x kg(-1), and anesthesia was induced with desflurane in 50% N(2)O and oxygen, using a normal tidal volume breathing technique. Subsequently, a preselected steady-state end-tidal desflurane concentration was maintained for 10 min before insertion of the LMA. Successful LMA insertion was defined as the absence of adverse airway responses until cuff inflation. Target concentrations of desflurane for LMA insertion were determined using a modified Dixon's up-and-down method (starting dose, 5%; step size, 0.5%).

All 22 patients completed the study without adverse events related to airway irritation. The EC(50) of desflurane for insertion of the LMA was determined to be 3.61 +/- 0.31%, and the 95% confidence interval (CI) of the EC(50) obtained using probit analysis was 3.13-3.90.

We demonstrated that N(2)O-desflurane inhalation induction with a normal tidal breathing technique after premedication with fentanyl can be used safely without any adverse airway events in nonparalyzed patients. In such patients, the EC(50) of desflurane for successful LMA insertion was 3.61 +/- 0.31% (95% CI, 3.13-3.90).