Propofol-fentanyl interaction for a flexible laryngeal mask airway insertion

Objectives: Flexible laryngeal mask airway (flexible LMA, FLMA) is a useful device for airway management during general anesthesia for minor oral surgery. Conversely to classical LMA (CLMA), no report has calculated EC50 and EC95 (the 50% and 95% effect site concentrations) of propofol required for FLMA insertion. This study was designed to determine EC50 and EC95 and to investigate whether supplemental 0.25µg/kg fentanyl decreases them.

Methods: Fifty-nine elective unpremedicated patients who were scheduled for minor oral surgery were randomly allocated to saline-propofol group (S-P group, n=30) or fentanyl-propofol group (F-P group, n=29). Each group was further divided into four subgroups in which the propofol EC for FLMA insertion was set at 2.5, 3.0, 3.5, and 4.0µg/ml in S-P group and 1.8, 2.0, 2.5, and 3.0µg/ml in F-P group, respectively. The experiment was assessed as “success” or “failure” based on FLMA insertion within 1 min. EC50 and EC95 were obtained from probit analysis.

Results: The EC50 and EC95 in S-P group were 3.29 (2.83-3.93, 95% confidential range) and 4.73 (3.94-12.22) µg/ml, and those in F-P group were 2.13 (1.42-2.60) and 3.54 (2.78-34.78) µg/ml, respectively. The EC50 in F-P group was significantly lower than that in S-P group. The probit regression line of propofol was shifted leftwards by combing fentanyl with propofol. There were no significant differences on bispectral index (BIS), hemodynamic variables, respiratory rate, and SpO2 between S-P and F-P groups.

Conclusions: The EC50 and EC95 in S-P group were 3.29 and 4.73µg/ml, and those in F-P group were 2.13 and 3.54µg/ml, respectively. Propofol EC50 for FLMA insertion was decreased by supplemental 0.25µg/kg fentanyl without hemodynamic and respiratory depression.