Low dose of fentanyl reduces predicted effect-site concentration of propofol for flexible laryngeal mask airway insertion

Abstract

Purpose

In contrast to reports on the classical laryngeal mask airway (classical LMA; CLMA), no report has calculated the 50% and 95% effect-site concentrations (EC₅₀ and EC₉₅, respectively) of propofol required for flexible LMA (FLMA) insertion. This study was designed to determine the EC₅₀ and EC₉₅ of propofol for FLMA insertion, using probit analysis, and to investigate whether supplemental 0.25 μg·kg⁻¹ fentanyl decreased these concentrations.

Methods

Fifty-nine unpremedicated patients who were scheduled for elective minor oral surgery were randomly allocated to a saline-propofol group (S-P group; n = 30) or a 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 4.0 μg·ml⁻¹, respectively, in the S-P group and 1.8, 2.0, 2.5, and 3.0 μg·ml⁻¹, respectively, in the F-P group,. The experiment was assessed as ”successful” when FLMA insertion within 1 min was possible.

Results

The EC₅₀ and EC₉₅ in the S-P group were 3.29 (95% confidence interval [CI], 2.83–3.93) and 4.73 (95% CI, 3.94–12.22) μg·ml⁻¹, and those in the F-P group were 2.13 (95% CI, 1.42–2.60) and 3.54 95% CI, (2.78-34.78) μg·ml⁻¹, respectively. The EC₅₀ in the F-P group was significantly lower than that in the S-P group. There were no significant differences in bispectral index (BIS), hemodynamic variables, respiratory rate, and arterial oxygen saturation ($Sp_{O_2 }$) between the S-P and F-P groups.

Conclusion

The propofol EC₅₀ for FLMA insertion was decreased by supplemental 0.25 μg·kg⁻¹ fentanyl without BIS, hemodynamic, or respiratory depression.