Intravenous lidocaine reduces the propofol EC50 for loss of consciousness and intraoperative anesthetic consumption in gynecological laparoscopy: A randomized controlled trial

Abstract: Background: Intravenous lidocaine reduces propofol requirements and procedure-related adverse events. Objectives: The study aimed to test whether intravenous lidocaine would reduce the effect-site concentration of propofol required to achieve loss of consciousness and decrease propofol consumption during total intravenous anesthesia in gynecological laparoscopy. Methods: This was a prospective, randomized, double-blind, placebo-controlled trial. Sixty patients were randomly allocated to receive either intravenous lidocaine (1.5 mg•kg-¹ bolus) followed by continuous infusion or an equal volume of saline. Propofol was administered via target-controlled infusion starting at an effect-site concentration of 3.5 μg/mL. The concentration was then adjusted in steps of 0.5 μg/mLaccording to Dixon’s up-and-down sequential method: decreased if loss of consciousness was achieved, or increased if not. Loss of consciousness was defined as loss of response to verbal commands. The median effective concentration (EC50) of propofol for inducing loss of consciousness was calculated using the Dixon’s up-and-down method. General anesthesia was maintained with propofol and remifentanil, guided by state entropy (target 40-60) and surgical pleth index (target 20-50). Drug consumption was normalized to anesthesia duration and body weight. Results: The estimated EC50 of propofol for inducing loss of consciousness was significantly lower in the lidocaine group than in the saline group (3.32 μg/mL, 95% Confidence Interval (CI): 3.04-3.59 vs. 3.89 μg/mL, 95% CI: 3.50-4.28). Under the study protocol, the lidocaine group also required less propofol (8.62 mg•kg-1•h-1, 95% CI: 8.10-9.15 vs. 9.89 mg•kg-1•h-1, 95% CI: 9.05-10.73) and less remifentanil (0.23 μg•kg-1•min-1, 95% CI: 0.21-0.24 vs. 0.27 μg•kg-1•min-1, 95% CI: 0.24-0.30) compared with the saline group. Conclusion: Intravenous lidocaine reduced the propofol EC50 for Loss of Consciousness (LOC) and decreased intraoperative propofol and remifentanil consumptions in patients undergoing gynecological laparoscopy. These findings suggest a propofol- and opioid-sparing effect of intravenous lidocaine in this setting, although confirmation in larger multicenter trials is needed.