Effects Of Dexmedetomidine On Mirror-image Pain Of Remifentanil-induced Hyperalgesia

Objective A number of studies have confirmed that remifentanil is possible to induce postoperative hyperalgesia.Our basic experiment had indicated the mirror-image pain of remifentanil-induced hyperalgesia（RIH）,but there is still lack of clinical evidence to support the occurrence of mirror-image pain of RIH.The study to investigate whether the use of remfentanil during the first total knee arthroplasty（TKA）in elderly patients can induce the mirror-image pain of RIH after the operation and dexmedetomidine can prevent the mirror-image pain of RIH or not.Methods 90 elderly patients were scheduled for the first total knee arthroplasty（TKA）,aged 60 to 80 years,ASAⅡorⅢ,BMI 18 to 30 kg/㎡were enrolled in our study.They were randomly divided into three groups which were 30 patients in each group.Patients in the low dose remifentanil group（RL group）were given the continuous intravenous infusion of remifentanil 0.1μg·（kg·min）^-1.Patients in the high dose remifentanil group（RH group）were given the continuous intravenous infusion of remifentanil 0.32μg·（kg·min）^-1.Patients in the high dose remifentanil+dexmedetomidine group（RD group）were given the continuous intravenous infusion remifentanil 0.32μg·（kg·min）^-1 and dexmedetomidine at the loading dose of 1.0μg·（kg·h）^-1（10 min）then the continuous intravenous infusion of the 0.3μg·（kg·h）^-1,which was stopped infusing 30 minutes before the end of surgery.The von Frey filaments were used to compare the mechanical pain thresholds（MPTs）of non-surgical knee before surgery and at 24 h,48 h after surgery.The visual analog scale（VAS）was used to compare the degrees of resting and exercising pain before surgery and in entering PACU,at 24 h,48 h after surgery in surgical side and non-surgical side.We recorded the perioperative hemodynamic;the Ramsay sedation scores of patients before surgery and after the removal of the throat mask,in entering PACU,and at 24 h,48 h after surgery,the postoperative analgesia quality（the time of postoperative analgesic requirements for the first time and the doses of sufentanil to remedy analgesia,the cases of postoperative rescue analgesia,the percent of postoperative analgesia satisfaction and the perioperative complications）.Results There were no significant differences among three groups for preoperative MPT in non-surgical side（P>0.05）.Compared with the preoperative level,the MPTs of non-surgical side were significantly decreased at 24 h and 48 h after surgery in RL group and RH group（P<0.05）.Compared with the RL group,the MPTs of non-surgical side were significantly decreased at 24 h and 48 h after surgery in RH group（P<0.05）.Compared with the RH group,the MPTs of non-surgical side were significantly increased at 24 h and 48 h after surgery in RD group（P<0.05）.There were no significant difference among three groups about the resting and exercising VAS scores in the surgical side and non-surgical side before surgery（P>0.05）.Compared with the preoperative level,the resting and exercising VAS scores were significantly increased in RL and RH groups in entering PACU and at 48 h after surgery in the surgical side and non-surgical side（P<0.05）;Compared with the RH group,the resting and exercising VAS scores were significantly decreased in RD groups at 48h after surgery in the surgical side and non-surgical side（P<0.05）.There were no significant differences among three groups about the perioperative blood pressure,SPO₂ and the Ramsay sedation scores（P>0.05）.The heart rate was lower than that of the other two groups after extubation in RD group（P<0.05）.Compared with the RH group,the patients with bradycardia were more,the time of postoperative analgesic requirements for the first time was prolonged,the doses of sufentanil to rescue analgesia,the cases of postoperative rescue analgesia were less,the percent of postoperative analgesia satisfaction was increased,the incidence of perioperative complications were decreased in RD group（P<0.05）.Conclusion The clinical observation of this randomized controlled study confirmed the existence of mirror pain of RIH.Dexmedetomidine can prevent the mirror-image pain of remifentanil-induced hyperalgesia.