| BackgroundSo far, postoperative pain is still to be a major problem of management of postoperative pain, and how to prevent postoperative acute pain into chronic pain has attracted increasing attention in recent years. Studies have shown that hyperalgesia caused by pain threshold such as mechanical pain threshold reduced plays a vital role in the process of postoperative acute pain into chronic pain. In fact, hyperalgesia impact the process of pain transfer, which could result in changes of neuronal plasticity, that lead to chronic pain, which takes some adverse effects to the patient. Therefore, the effective prevention of postoperative mechanical pain threshold lowered and avoiding hyperalgesia is the effective ways or strategies prevention of postoperative acute pain into chronic pain. However, there is not ideal clinical method to prevent postoperative hyperalgesia or pain threshold lowered.Research shows that dexmedetomidine increased attention in recent years is expected to become an effective means of prevention and treatment of postoperative pain hypersensitivity. Dexmedetomidine is a highly selective a2agonists, animal studies have found that given dexmedetomidine can improve the mechanical pain threshold in rats, and this role in nerve injury more powerful, therefore, we hypothesized that dexmedetomidine can inhibit humans postoperative hyperalgesia. However, whether dexmedetomidine can prevent postoperative hyperalgesia clinically is not yet clear. Although some domestic clinical data found that dexmedetomidine can reduce postoperative pain scores, further speculated dexmedetomidine can reduce the occurrence of hyperalgesia, but postoperative pain visual analogue scale is behavior score or self-scoring affected by environmental, psychological or subjective factors, so according to the visual analog scale to determine whether they can prevent the occurrence of hyperalgesia is not reliable, because VAS ratings increased does not reflect reduced of the pain threshold. To determine the occurrence of hyperalgesia by Quantitative sensory test, so far, widely recognized as a measure of hyperalgesia is the change of pain threshold, such as mechanical pain threshold,However, the impact of Dex on postoperative mechanical pain threshold has not been reported in domestic, so we intend to investigate the effect of Dex on postoperative mechanical pain threshold in patients, to clear whether Dex can prevent the occurrence of postoperative hyperalgesia and to discuss the significance of Dex inhibition of hyperalgesia.ObjectiveTo observe the effects of dexmedetomidine on postoperative mechanical pain threshold in different parts of patients, To confirm whether dexmedetomidine can prevent hyperalgesia, comparing difference of hyperalgesia between dexmedetomidine and parecoxib. That can provide the basis and tools for acute postoperative hyperalgesia and even chronic pain prevention and treatment, provide a reference for the rational use of drugs in clinical anesthesia.MethodsAccording to internationally accepted standards to determine hyperalgesia is the changes of pain threshold, mechanical pain threshold was measured in patients by the use of von Frey filaments. Because whether intraoperative and postoperative analgesia may affect the results of observations of dexmedetomidine, we will first observe the effect of dexmedetomidine on the different time points of mechanical pain threshold of the patients undergoing thyroid surgery (can not need postoperative pain), then observing the effect of dexmedetomidine after chest surgery patients (intense pain, need postoperative pain, become chronic pain easier) on the changes of mechanical pain threshold. The research process is divided into two parts:1, The impact of dexmedetomidine on postoperative mechanical pain threshold in patients undergoing thyroid surgerywe taked the completely random grouping method.80patients undergoing elective thyroidectomy were randomly divided into four groups:dexmedetomidine group (HD group), high dose remifentanil group(HI group), parecoxib sodium group (HP group) low dose remifentanil group (LO group).The patients in HD group received dexmedetomidine1.0ug-kg-1in10min before induction of anesthesia, and given0.4ug-kg-1·h-1continuous infusion of dexmedetomidine until1hour before the end of surgery, and given remifentanil0.2ug-kg-1·min-1.The patients in LO group and HI group received normal saline infusion replaced dexmedetomidine, given remifentanil0.05ug·kg-1·min-1and0.2ug·kg-1·min-1respectively. The patients in HP group received normal saline infusion replaced dexmedetomidine, and at the time of skin closure intravenous parecoxib sodium40mg. Mechanical pain thresholds on forearm and periincisional area were assessed by von Frey filament. mechanical pain thresholds were recorded before surgery, and at2,4,8,12,24,48h postoperation, additional VAS score and postoperative adverse reactions within48h were recorded. 2, The impact of dexmedetomidine on postoperative mechanical pain threshold in patients undergoing chest surgery(1) The impact of dexmedetomidine on postoperative mechanical pain threshold in patients undergoing mastectomywe taked the completely random grouping method.40patients undergoing elective mastectomy were randomly divided into two groups: Dexmedetomidine group (BD group),remifentanil group (BR group). The patients in BD group received dexmedetomidine1.0ug·kg-1in10mins before induction of anesthesia, and given0.4ug·kg-1·h-1continuous infusion of Dex until1hour before the end of surgery. The patients in BR group received received normal saline infusion replaced dexmedetomidine before induction of anesthesia and Intraoperation. Anesthesia was maintained using remifentanil with sevoflurane, remifentanil began pumping from0.2ug·kg-1min-1until the end of the operation.(2) The impact of dexmedetomidine on postoperative mechanical pain threshold in patients undergoing thoracotomywe taked the completely random grouping method.40patients undergoing elective thoracotomy were randomly divided into two groups:Dexmedetomidine group (TD group),remifentanil group (TR group). The patients in TD group received dexmedetomidine1.0ug·kg-1inlOmins before induction of anesthesia, and given0.4ug·kg-1·h-1continuous infusion of dexmedetomidine until1hour before the end of surgery. The patients in TR group received received normal saline infusion replaced dexmedetomidine before induction of anesthesia and Intraoperation. Anesthesia was maintained using remifentanil with sevoflurane, remifentanil began pumping from0.2ug·kg-1min-1until the end of the operation.Mechanical pain thresholds on forearm and periincisional area were assessed by von Frey filament. mechanical pain thresholds were recorded before surgery, and at2, 4,8,12,24,48h postoperation, additional VAS score and postoperative adverse reactions within48h were recorded.Results1, The impact of dexmedetomidine on postoperative mechanical pain threshold in patients undergoing thyroid surgerycompared Mechanical pain thresholds on the periincisional area with the preoperative mechanical pain thresholds in the HI group are significantly decreased (P<0.05), In the HD group at8h,12h,24h,48h, compared with the preoperative,are significantly increased (P<0.05), In the HP group at4h,8h,12h, compared with the preoperative,are significantly increased (P<0.05),and decreased in the LO group,but the difference was not statistically significant (P>0.05) Compared with the HI group,The HD group are higher at8,12,24h,48h (P<0.05), The HP group are higher at4h,8h (P<0.05), HI group compared with the LO group is significantly lower in the postoperation (P<0.01), Compared with the HP group/The HD group are higher at12h,24h,48h (P<0.05).The change of pain threshold on the forearm was similar among the groups, compared Mechanical pain thresholds with the preoperative mechanical pain thresholds in the HI group are significantly decreased (P<0.05), In the HD group at8h,12h,24h,48h, compared with the preoperative,are significantly increased (P<0.05), In the HP group at4h,8h,12h, compared with the preoperative,are significantly increased (P<0.05),and decreased in the LO group,but the difference was not statistically significant (P>0.05). Compared with the HI group.The HD group are higher at8,12,24h,48h (P <0.05), The HP group are higher at4h,8h (P<0.05), HI group compared with the LO group is significantly lower in the postoperation (P<0.01), Compared with the HP group,The HD group are higher at12h,24h,48h (P<0.05). Additional VAS values compared with preoperative were significantly increased(P<0.05), but VAS value compared among the four groups is not statistically significant (P>0.05) Furthermore, we found that postoperative VAS values and mechanical pain threshold in patients have no correlation. The incidence of adverse reactions compared among the four groups is not statistically significant (P>0.05)2, The impact of dexmedetomidine on postoperative mechanical pain threshold in patients undergoing chest surgery(1) The impact of dexmedetomidine on postoperative mechanical pain threshold in patients undergoing mastectomycompared Mechanical pain thresholds on the periincisional area with the preoperative mechanical pain thresholds in the BR group are significantly decreased (P<0.05), In the BD group compared with the preoperative,are significantly increased (P<0.05), Compared with the BR group.The BD group are higher at4h,8h,12h,24h (P<0.05). The change of pain threshold on the forearm was similar among the groups.Additional VAS values compared with preoperative were significantly increased(P<0.05), but VAS value compared between the two groups is not statistically significant. The incidence of adverse reactions compared between the two groups is not statistically significant (P>0.05)(2) The impact of dexmedetomidine on postoperative mechanical pain threshold in patients undergoing thoracotomycompared Mechanical pain thresholds on the periincisional area with the preoperative mechanical pain thresholds in the TR group at2h,4h,8h,12h,24h are significantly decreased (P<0.05), In the TD group compared with the preoperative,are significantly increased (P<0.05), Compared with the TR group,The TD group are higher at4h,8h,12h (P<0.05). The change of pain threshold on the forearm was similar among the groups. Compared VAS value with TR groups, TD group at4h,8h,12h are significantly decreased(P<0.05); The incidence of adverse reactions compared between the two groups is not statistically significant (P>0.05)Conclusion1Intraoperative large doses of remifentanil can cause reduced of mechanical pain threshold after surgery, indicating that large doses of remifentanil lead to postoperative hyperalgesia. Dexmedetomidine can improve postoperative mechanical pain threshold, which can prevent postoperative hyperalgesia caused by large doses of remifentanil. Compared with parecoxib sodium, dexmedetomidine is superior longer than parecoxib sodium in the difference of hyperalgesia.2Postoperative mechanical pain threshold significantly reduced in the patient undergoing Mastectomy or thoracotomy with large doses of remifentanil anesthesia, indicating that these patients suffered postoperative hyperalgesia, therefore dexmedetomidine can inhibit postoperative mechanical pain threshold reduced in the patient underging chest surgery, and can reduce hyperalgesia after such surgery. |
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