| BACKGROUNDPain sensibility significantly increases and the threshold to noxious thermal and mechanical stimuli decreases when patients are treated with opiods drugs for a long time. It is opiod-induced hyperalgesia (OIH). Remifentanil, an new ultra-short acting selective μ-opioid receptor agonist, has the advantage of fast onset of action, powerful analgesic effect, no accumulation and rapid recovery. It has a wide range of applications in clinical anesthesia. But numerous clinical studies have suggested that the patients would experience breakthrough pain and/or hyperalgesia, and further need more analgesic drugs. Then it brings more complications and a big challenge for postoperative pain management. The problems, which how to prevent and treat hyperalgesia induced by remifentanil and its mechanism, become a focused issue.In clinical, opiods drugs have been intravenous injected for preventing hyperalgesia induced by remifentanil. But opiods drugs just cover up hyperalgesia for its analgesia, it can not radically eliminate hyperalgesia. Some studies reported that cyclooxygenase (COX) get involved in pathogenesis of OIH, and COX antagonist, such as parecoxib sodium and flurbiprofen, can effectively alleviate postoperative hyperalgesia induced by remifentanil. Other drugs, such as ketamine, clodine and so on, can suppress hyperalgesia in some studies, while it has still controversy. A meta analysis of14prospective, randomized multicenter studies about NMDA antagonist used in postoperative hyperalgesia, suggested NMDA antagonist could not effectively prevent postoperative hyperalgesia and tolerance induced by remifentanil.The mechanism of hyperalgesia induced by remifentanil is not clear. The underlying mechanisms are related to decrease of endogenous μ-receptor and activation of NMDA receptor. Spinal cord is also important for opiods tolerance and hyperalgesia. Spinal astrocyte (AS) is closely associated with pain. In pathological status, astrocytes would be activated and further release a lot of inflammatory mediums, cytokines and neuroactive substances, including active pain substances, such as P substance, arachidonate, prostaglandin, EAA, TNF, and so on. Microglia cell is firstly activated by pro-inflammatory cytokines, then AS is activated. In return, activated AS will feedback activate microglia cell to forming a positive feedback. Studies suggested OIH induced by morphine was related to activation of spinal gliocyte. So, the effect of spinal gliocyte in mechanism of hyperalgesia induced by remifentanil will be interesting to study.Acupuncture is Chinese traditional medicine, and has also been accepted by a lot of western countries. Electro-acupuncture stimulation (EAS) has been treated for many diseases, as pain, stroke. EAS is one effective auxiliary analgesic method and its effect is confirmed. In recent, some reports suggested the main mechanism of acupuncture was related to increasing endogenous opiods,5-HT and adenosine, and so on. Studies have reported that EAS could alleviate morphine tolerance, but effect of EAS on hyperalgesia induced by remifentanil is seldom reported. Then, this study will explore the effects of EAS on hyperalgesia induced by remifentanil and its underlying mechanism through clinical application and animal experiment.OBJECTIVEPart Ⅰ clinical study:To observe the analgesic effect of EAS of Ximen (PC4) and Neiguan (PC6) on breakthrough pain induced by remifentanil in patients undergoing radical thoracic esophagectomy, and to explore the plasma β-EP, PGE2and5-HT levels to discuss the underlying mechanismsPart Ⅱ animal experiment1. To establish rat hyperalgesia model induced by remifentanil after incision, and to observe the GFAP expression and OX-42level in spinal microglia cells. 2. To observe the effect of EAS on the expression of GFAP and OX-42in spinal microglia cells, and to explore underlying mechanism.METHODSPart Ⅰclinical study:Sixty patients (ASAⅢ) scheduled for elective radical esophagectomy were randomized into three groups:group A (control) receiving a general anesthesia only; group B (sham) given EA needles at PC4(Ximen) and PC6(Neiguan) but no stimulation; and group C (EAS) electrically given EAS of the ipsilateral PC4and PC6throughout the surgery. The EAS consisted of a disperse-dense wave with a low frequency of2Hz and a high frequency of20Hz, was performed30min prior to induction of general anesthesia and continued through the surgery. At the emergence, sufentanil infusion was given for postoperative analgesia with loading dose of7.5μg, followed by a continuous infusion of2.25μg/h. The patient self-administration of sufentanil was0.75μg with a lockout of15min as needed. Additional breakthrough pain was treated with dezocine (5mg) intravenously at the patient’s request. Blood samples were collected before (T1), and2h (T2),24h (T3), and48h (T4) post-operation to measure the plasma β-EP, PGE2, and5-HT. The operative time, the total dose of sufentanil and the dose of self-administration, and the rescue doses of dezocine were recorded. Visual Analogue Scale (VAS) scores at2,12,24and48h postoperatively and the incidence of apnea and severe hypotension were recorded.Part Ⅱ animal experimentAnimals were divided into the following four groups according to different treatment in rat hyperalgesia model induced by remifentanil. Group Ⅰ (incision pain model group):Rat incisional pain model was established; and intraoperative normal saline (3ml/h, total60min) were intravenous injected. Group R (Remifentanil treatment group):The rat incisional pain model was established as Group Ⅰ, then the model was intravenous injected with remifentanil (80ug/kg,3ml/h, treatment lasted60min, batch number6130502, from Yichang Renfu Pharmaceutical company). Group R+T (EAS group):After anesthesia, Huantiao which was located in hip joint posterior upper edge (sciatic nerve stem near around the greater trochanter of femur) and Yanglingquan which was located in5mm below fibulae capitulum (sural nerve and tibial nerve) acupoints of the right side were selected. And Electroacupuncture stimulation (EAS)(2Hz/15Hz,1mA) began30mim before establishing incisional pain model, and remifentanil (80ug/kg, treatment lasted60min) were continuous intravenous injected. Group R+F (sham group):Electric needle is inserted into the sham acupoints after anesthesia. EAS began30mim before establishing incisional pain model, and remifentanil (80ug/kg, treatment lasted60min) were continuous intravenous injected. PWT and PWL at baseline (24hours before incision) and4,12,24, and48hours after remifentanil infusion were tested. These rats were sacrificed at different time points (4h,24h,48h)。GFAP and OX-42were measured by Western blot analysis, Enzyme linked immunosorbent assay (ELISA), respectively.RESULTSPart Ⅰ clinical study:Patients in EAS group had the lowest VAS scores postoperatively among the three groups (P<0.05). The total dose of sufentanil was115±6.0μg in EAS group, significantly lower than that in control (134.3±5.9) μg and sham (133.5±7.0) μg groups. Similarly, the rescue dose of dezocine was the least in EAS group (P<0.05) among the three groups. Plasma p-EP levels in EAS group at T3(176.90±45.73) and T4(162.96±35.00) pg/mL were significantly higher than in control (132.33±36.75and128.79±41.24) pg/mL and sham (136.56±45.80and129.85±36.14) pg/mL groups, P<0.05for all. EAS could decrease the release of PGE2. Plasma PGE2levels in EAS group at T2and T3(41±5and40±5) pg/mL respectively were significantly lower than in control (64±5and62±7) pg/mL and sham (66±6and62±6) pg/mL groups. Plasma5-HT levels in EAS group at T2(133.66±40.85) and T3(154.66±52.49) ng/mL were significantly lower than in control (168.33±56.94and225.28±82.03) and sham (164.54±47.53and217.74±76.45) ng/mL groups. For intra-group comparison, plasma5-HT and PGE2levels in control and sham groups at T2and T3, and β-EP in EAS group at T3and T4were significantly higher than at T1(P<0.05); PGE2and5-HT levels in EAS group showed no significant difference among the different time points (P>0.05). No apnea or severe hypotension was observed in any group.Part II animal experiment1. The baseline of PWT and PWL values in each group were undifferentiated. Postoperative PWT and PWL values were significantly lower in Group R+T than the other three groups. Postoperative PWT and PWL values in four groups were significantly lower than baseline, and the value gradually decreased to lowest at24h after operation (P<0.05).2. GFAP expression and OX-42concentration in Group R and R+F were significantly higher than those in Group I and R+T (P<0.05).CONCLUSIONS1. Intraoperative ipsilateral EAS at PC4and PC6provides effective postoperative analgesia for patients undergoing radical esophagectomy with remifentanil anesthesia and significantly decrease requirement for parental narcotics. The underlying mechanism may be related to the release of endogenous (3-EP and inhibiting of inflammatory mediators (5-HT and PGE2)2. In the animal hyperalgesia model induced by remifentanil, the-GFAP was overexpressed and concentration of OX-42was significantly increased in spinal glial cells. Postoperative pain threshold of the rats model were significantly elevated in EAS group. The underlying mechanism of effect of EAS on hyperalgesia induced by remifentanil is related to inhibiting the activation of the spinal glial cells. |
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