Fentanyl dose–response curves when inserting the LMA Classic™ laryngeal mask airway

Summary Probit analysis was used to predict an optimal dose of fentanyl, co‐administered with propofol 2.5 mg.kg−1, when inserting the laryngeal mask airway. In all, 21 male and 54 female healthy Chinese patients, aged 18–63 years, requiring anaesthesia for minor surgery were recruited. They were assigned to one of five groups: placebo, 0.5, 1.0, 1.5 and 2.0 μg.kg−1. Insertion was performed 90 s after administration and insertion conditions assessed using a six‐category score. Dose–response curves could only be drawn for swallowing and movement categories, and only the ED50 could be predicted with certainty. To provide optimal conditions in over 95% of patients, fentanyl doses well above the clinical range were required. A standard fentanyl dose of 1 μg.kg−1, co‐administered with propofol 2.5 mg.kg−1, provided optimal conditions in 65% of cases. Ninety seconds may have been insufficient time for fentanyl to reach its peak effect.