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

Abstract

In contrast to reports on the classical laryngeal mask airway (classical LMA; CLMA), no report has calculated the 50% and 95% effect-site concentrations (EC(50) and EC(95), respectively) of propofol required for flexible LMA (FLMA) insertion. This study was designed to determine the EC(50) and EC(95) of propofol for FLMA insertion, using probit analysis, and to investigate whether supplemental 0.25 microg x kg(-1) fentanyl decreased these concentrations. 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 microg x ml(-1), respectively, in the S-P group and 1.8, 2.0, 2.5, and 3.0 microg x ml(-1), respectively, in the F-P group. The experiment was assessed as "successful" when FLMA insertion within 1 min was possible. The EC(50) and EC(95) 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) microg x 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) microg x ml(-1), respectively. The EC(50) 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 (SpO2) between the S-P and F-P groups. The propofol EC(50) for FLMA insertion was decreased by supplemental 0.25 microg x kg(-1) fentanyl without BIS, hemodynamic, or respiratory depression.