The Median Effective Dose(ED50) Of Single Intravenous Oxycodone For Postoperative Analgesia Following Gynecological Surgical Procedures

Objective: To estimate the median effective dose(ED50)of one intravenous bolus of oxycodone inhibiting acute postoperative pain in patients undergoing myomectomy and hysterectomy combined with ropivacaine local infiltration analgesia.Explore the effect of a single intravenous injection of oxycodone on mean blood pressure(MBP)and heart rate(HR)as well.Methods: In this dose-finding study,the ED50 of oxycodone for postoperative analgesia was estimated separately for laparoscopic hysterectomy,transabdominal hysterectomy,laparoscopic myomectomy and transabdominal myomectomy.We used the sequential allocation designed by Dixon.Trials were conducted simultaneously in the four surgical type groups.A predefined dose of oxycodone was injected 30 minutes before the end of the operation with an initial dose of 0.1 mg/kg.A series of trials were carried out following the rule of a relative 10% increase in dose following inadequate analgesia and a relative 10% decrease in dose following adequate analgesia.The study was conducted until the collection of seven crossover points was achieved.Local ropivacaine wound infiltration was administered during abdominal stitching.The mean blood pressure(MBP)and heart rate(HR)were analyzed to assess the hemodynamic changes associated with oxycodone administration.Results: A total of 113 patients were included in the estimation of ED50: 28 each in the laparoscopic hysterectomy group and transabdominal myomectomy group,27 in the transabdominal hysterectomy group and 30 in the laparoscopic myomectomy group.The estimated oxycodone ED50(95% CI)following laparoscopic hysterectomy,transabdominal hysterectomy,laparoscopic myomectomy,and transabdominal myomectomy was 0.060 mg/kg(0.053,0.068),0.079 mg/kg(0.072,0.086),0.060 mg/kg(0.051,0.071),and 0.092 mg/kg(0.086,0.098),respectively,for postoperative analgesia with local ropivacaine wound infiltration.The ED50 of oxycodone was different between laparoscopic surgeries and transabdominal surgeries(P <0.001).The MBP and HR before and after oxycodone injection were different,regardless of surgical type.Conclusions: The oxycodone ED50 for postoperative analgesia was lower for laparoscopic hysterectomy(0.060 mg/kg)and laparoscopic myomectomy(0.060 mg/kg)than for transabdominal hysterectomy(0.079 mg/kg)and transabdominal myomectomy(0.092 mg/kg)when combined with local ropivacaine wound infiltration.A single intravenous injection of oxycodone is associated with an acceptable decrease in blood pressure and HR within a short time.