Modulation Of Remifentanil-Induced Postoperative Hyperalgesia And Tolerance By Subhypnotic Doses Of Propofol

Objective:(1)To investigate the phenomenon that intraoperative remifentanil administration results in acute opioid tolerance and hyperalgesia.(2)To investigate the postoperative analgesic effect of subhypnotic doses of propofol used on remifentanil-induced acute opioid tolerance and hyperalgesia.Method:A total number of sixty ASAI～Ⅲadult patients who undergoing major abdominal surgery were assigned randomly to three anesthetic regimens.Each group was induced with midazolam 0.1 mg/kg, atracurium 0.5mg/kg,remifentanil 1.0μg/kg intravenous injection and endotracheal,and then they were administrated as follows:(1)remifentanil at 0.1μg·kg^-1·min^-1and isoflurane titrated to autonomic responses (groupⅠ);(2)isoflurane was kept constantly at 0.5 minimum alveolar concentrations and a remifentanil infusion was titrated to autonomic responses(groupⅡ);(3)isoflurane was kept constantly at 0.5 minimum alveolar concentrations and a remifentanil infusion was titrated to autonomic responses,the patients were given a bolus of 1.0μg·kg^-1·min^-1 propofol when remifentanil was discontinued until 15 minutes after tracheal extubation(groupⅢ).Isoflurane and remifentanil was discontinued 15 minutes before the end of the operation in each group,fentanyl was injected intravenously accroding to MAP,SBP,HR and Pain scores in each group from the monment that remifentanil was discontinued.Pain scores and fentanyl consumption were recorded for 24 postoperative hours.Result:The mean remifentanil infusion rate was(0.26±0.17)μg·kg^-1·min^-1and(0.27±0.28)μg·kg^-1·min^-1in groupⅡand groupⅢrespectively,which are significantly greater than that in groupⅠ. Intraoperative hemodynamic responses were similar in each group.The emergence time,extubation time and the postoperative complications were also similar.Postoperative pain scores were significantly greater in groupⅡ.These patients required fentanyl significantly earlier than those in groupⅠand groupⅢ(P<0.05),and fentanyl comsumption were much more than that in the other two groups in the first 24 postoperative hours (P<0.05)Conclusion:(1)Relatively large-dose of intraoperative remifentanil increased postoperative pain and fentanyl consumption.These data suggest that remifentanil causes acute opioid tolerance and hyperalgesia.(2)Subhypnotic doses of propofol had significant suppressive effect on patients with postoperative hyperalgesia and acute opioid tolerance after remifentanyl anesthesia.