Abstract: AIM: To investigate the effective dose of esketamine for prevention on propofol injection pain in painless abortion.  METHODS: From November 2021 to December 2021, thirty patients undergoing painless abortion, aged 20 to 40 years old, ASA physical status Ⅰ or Ⅱ, BMI 19-26 kg/m2 were enrolled. The experiment was used with a modified Dixon up and down method. The initial dose of esketamine was 0.2 mg/kg, and the dose gradient of esketamine in adjacent patients was 0.02 mg/kg. When propofol injection pain was positive, the next patient was given a high first-order dose, otherwise a low first-order dose was used, and the experiment ended when the 7th crossovers were appeared. The ED50, ED95 and the corresponding 95% confidence interval (CI) of esketamine were calculated by Probit analysis. The values of MAP, SpO2 and HR were recorded before injection (T0), after esketamine injection (T1), after propofol injection (T2) and after operation (T3). At the same time, the adverse reactions such as awakening time, nausea and vomiting, delirium and abnormal vision were observed and recorded. RESULTS: The ED50, ED95 and 95%CI of esketamine for prevention on propofol injection pain were 0.135 (0.116-0.149) mg/kg and 0.170 (0.153-0.252) mg/kg. Compared with T0, the value of MAP at T1 was significantly higher, the value of MAP and SpO2 at T2 were significantly lower (P<0.05), and the recovery time was (7.2±3.1) min. No adverse reactions such as nausea and vomiting, postoperative agitation, delirium and abnormal vision occurred in all patients. CONCLUSION: The ED50 and ED95 of esketamine for prevention on propofol injection pain were 0.135 mg/kg and 0.170 mg/kg, respectively. Low dose of esketamine can effectively prevent the pain of propofol injection during painless abortion and maintain the stability of hemodynamics.

Key words: esketamine, propofol, injection pain, painless abortion