Optimal lidocaine propofol mixture for painless induction of anesthesia

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.

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.

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.

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).