Abstract: OBJECTIVE To investigate the effect of intravenous lidocaine on the half effective dose(ED₅₀) of alfentanil under propofol anesthesia to suppress the somatic motor response in patients undergoing artificial abortion surgery. METHODS Patients preparing to receive artificial abortion surgery, aged 18-40 years, with American Society of Anesthesiologists classification I-II were selected. They were randomly divided into two groups, lidocaine combined with alfentanil group(group LA) and alfentanil group(group A). Patients in the group LA received intravenous lidocaine 1.0 mg·kg^-1 followed by slow injection of propofol 2.0 mg·kg^-1 and alfentanil(initial dose of 15.5 μg·kg^-1). In group A, patients were given 0.1 mL·kg^-1saline intravenously followed by slow injection of propofol 2.0 mg·kg^-1 and alfentanil sequentially, and after the patients lost consciousness, disinfected towels were spread and the patients were observed for somatic motor response to the placement of the cervical probe. The dose of alfentanil was calculated using the sequential method, and if a positive somatotropic reaction occurred at the time of placement of the uterine probe, the dose was increased by 20% in the next patient and decreased by 20% in the opposite case. The test was terminated when more than six alternating points of positive and negative reactions occurred. Probabilistic unit regression analysis was used to calculate the ED₅₀value, the 95% effective dose(ED₉₅) value and its 95% confidence interval(CI) for alfentanil suppression of somatic motor response in patients undergoing abortion. Intraoperative vital signs, intravenous pain, pain scores at 10 min after surgery, 30 min after surgery, and discharge were recorded. RESULTS The ED₅₀ value in group LA was 6.55 μg·kg^-1(95%CI, 2.10-8.07 μg·kg^-1). The ED₅₀ value in group A were 8.24 μg·kg^-1(95%CI, 6.75-9.75 μg·kg^-1). There was a difference in the ED₅₀value for alfentanil in the two groups. The group LA had statistically lower pain score at 10 min after surgery, 30 min after surgery, and discharge compared with group A, the difference was statistically significant(P<0.000 1 or P<0.05). In group LA, the incidence of intravenous excision decreased(decrease by 44.2%), and the difference was statistically significant(P<0.0l). There was no statistically significant difference in the number of cases of respiratory depression, awake time and nausea and vomiting between the two groups. CONCLUSION Intravenous lidocaine can significantly reduce the ED₅₀ value of alfentanil for abortion surgery, reduce the incidence of intravenous pain, and relieve short-term acute postoperative pain.