Optimal lidocaine propofol mixture for painless induction of anesthesia

Objective: To determine the median effective dose (ED50) of 2% lidocaine mixed with propofol for preventing pain during the induction of anesthesia using a modified Dixon’s up-and-down method. Materials and Methods: Thirty ASA (American Society of Anesthesiologists) grade I and II patients, aged 18–60 years, undergoing elective surgery were enrolled. Using the modified Dixon’s up-and-down method, patients received varying doses of lidocaine mixed with 20 mL of propofol MCT/LCT (Medium Chain Triglyceride/Long Chain Triglyceride) emulsion. The primary outcome was the calculation of the ED50 of 2% lidocaine, defined as the midpoint dose at which 50% of patients experienced painless injection. Secondary outcomes included pain scores during injection, heart rate changes, and withdrawal movements. Results: Thirty patients completed the study. The ED50 of lidocaine premixed with 20 mL of propofol MCT/LCT emulsion to prevent pain during the induction of anesthesia was 32.14 mg (95% CI = 32.09 mg–32.18 mg), equivalent to 1.46 mg/mL (95% CI: 1.02 mg/mL–1.91 mg/mL). Demographic and clinical characteristics of patients who experienced pain and those who did not were not statistically significant. Conclusion: Our study concluded that the ED50 of lidocaine premixed with 20 mL of propofol to prevent pain during the induction of anesthesia was 32.14 mg (95% CI = 32.09 mg–32.18 mg), equivalent to 1.46 mg/mL (95% CI: 1.02–1.91 mg/mL).