The Effect of Intravenous Lidocaine on EC50 of Remifentanil for Preventing Cough During Emergence in Female for Thyroid Surgery Anesthesia.

Objective: To evaluate the effect of intravenous lidocaine injection on the half-maximum effective concentration (EC50) of remifentanil in preventing cough due to tracheal extubation in female patients undergoing thyroid surgery by Dixon's sequential method.

Methods: A total of 50 female patients underwent elective thyroidectomy were randomly divided into two groups of a 1:1 ratio. Group L (lidocaine group) was given intravenous lidocaine (1.5 mg/kg) and then continuous infusion (2 mg/kg/h) until the end of surgery. Group C (control group) received 0.9% sodium chloride solution infusion in the same way. The primary outcome was effective concentration EC50 of remifentanil in preventing cough due to tracheal extubation in female patients undergoing thyroid surgery. The secondary outcomes were as follows: mean arterial pressure (MAP), oxygen saturation (SpO₂), heart rate (HR), PetCO₂ and respiratory rate at the time of tracheal extubation. The incidence of postoperative nausea and vomiting, and symptoms associated with lidocaine toxicity.

Results: Finally, 44 subjects completed the study. The EC50 values of remifentanil calculated using probit regression were 1.40 ng/mL (95% CI, 1.15-1.65 ng/mL) in Group C and 0.83 ng/mL (95% CI, 0.58-1.08 ng/mL) in Group L. A lower concentration of remifentanil can inhibit the cough reaction during intravenous lidocaine infusion. PetCO₂ in the lidocaine group was lower than that in the control group (Z=-2.162, P < 0.05). The respiratory rate of the lidocaine group after extubation was higher than that of the control group (Z=-3.287, P < 0.05).

Conclusion: Intravenous injection of lidocaine can reduce the effective concentration EC50 of remifentanil in preventing tracheal extubation cough in female patients undergoing thyroid surgery.