Dose-response relationship of ketamine for inhibiting postoperative hyperaigesia after remifentanil-based anesthesia

Abstract

Objective To investigate the dose-response relationship of ketamine for inhibiting postoperative hyperalgesia after remifentanil-based anesthesia in patients undergoing laparoscopic cbolecystectomy. Methods Fifteen ASA Ⅰ or Ⅱ patients aged 40-60 yr, weighing 45-80 kg undergoing laparuscopic cholecystectomy under remifentanil-based general anesthesia were studied. The patients were premedicated with intramuscular atropine 0.5 mg. Anesthesia was induced with midazolam 0.05 mg/kg, fentanyl 4 μg/kg, propofol ventilated after tracheal intubatiun. Ketamine was given before skin incision for inhibiting remifentanil-induced postoperative hyperalgesia. Pain was assessed using VAS (0 = no pain, 10 = worst pain) at 10 min after tracheal extubation. VAS score < 4 was defined as effective. The optimal dose was determined by Dixon's up-and-down method. If the VAS score was < 4, the next patient received a lower dose of ketamine, or conversely if ineffective, a higher dose was given in the next patient. The up-and-down sequences were analyzed by using probit method to determine the ED50, ED95 and 95% confidence interval (CI). Results The ED50 of ketamine for inhibiting postoperative hyperalgesia after remifentanil-based anesthesia was 0.23 mg/kg (95% CI 0.12-0. 35 mg/kg) and ED95 0.62 mg/kg (95 % CI 0.51-0.68 mg/kg). Conclusion The ED50 and ED95 of ketamine for inhibiting postoperative hyperalgesia after remifentanil-based anesthesia in patients following laparoscopic cholecystectomy are 0.23 mg/kg and 0.62 mg/kg respectively. Key words: Ketamine; Pipefidines; Hyperalgesia; Dose-response relationship,drug