The Effect of a Bolus Dose of Intravenous Lidocaine on the Minimum Alveolar Concentration of Sevoflurane: A Prospective, Randomized, Double-Blinded, Placebo-Controlled Trial

BACKGROUND: The anesthetic effect of volatile anesthetics can be quantified by the minimum alveolar concentration (MAC) of the drug that prevents movement in response to a noxious stimulus in 50% of patients. The underlying mechanism regarding how immobilization is achieved by volatile anesthetics is not thoroughly understood, but several drugs affect MAC. In this study, we investigated the effect of a single IV bolus dose of lidocaine on the MAC of sevoflurane in humans. METHODS: We determined the MAC for sevoflurane using the Dixon up-and-down method in 3 groups of patients, aged 30 to 65 years, who underwent elective surgery (30 patients per group). Study medication (placebo, 0.75 mgkg(-1) lidocaine or 1.5 mgkg(-1) lidocaine) was administered 3 minutes before skin incision after a 15-minute equilibration period and the response to skin incision was recorded (movement versus no movement). RESULTS: MAC was 1.86% 0.40% in the placebo and 1.87% +/- 0.45% in the 0.75 mgkg(-1) lidocaine group (P = 1.00). MAC was 1.63% +/- 0.24% in the 1.5 mgkg(-1) lidocaine group, which was significantly lower than that of the placebo group (mean difference of 0.23% sevoflurane [95% adjusted confidence interval {CI}, 0.03-0.43]; P = 0.022). No significant difference was observed between the 0.75 mgkg(-1) lidocaine and the placebo groups (mean difference of -0.01% sevoflurane [95% adjusted CI, -0.27 to 0.25]; P = 1). CONCLUSIONS: IV 1.5 mgkg(-1) lidocaine decreased the MAC by at least 0.03% sevoflurane (mean difference 0.23% sevoflurane [95% adjusted CI, 0.03-0.43]). We did not observe a significant reduction in the MAC of sevoflurane with the IV administration of 0.75 mgkg(-1) lidocaine.