鞘内注射右旋美托咪啶对大鼠罗哌卡因蛛网膜下腔阻滞效果的影响

Effects of intrathecal dexmedetomidine on ropivacaine spinal block in rats

目的探讨鞘内注射右旋美托咪啶对大鼠罗哌卡因蛛网膜下腔阻滞效果的影响。方法清洁级雄性SD大鼠，体重250—300g，取鞘内置管成功的大鼠36只，随机分为6组（n=6），C组：鞘内注射生理盐水20．出；D组：鞘内注射右旋美托咪啶3,ug／kg20μl；R组：鞘内注射0．5％罗哌卡因20脚；DR，组：鞘内注射右旋美托咪啶1μg／kg＋0．5％罗哌卡因20μl；DR2组鞘内注射右旋美托咪啶2μg/kg＋0．5％罗哌卡因20μl；DR3组鞘内注射右旋美托咪啶3μg／kg＋0．5％罗哌卡因20m。于鞘内注药前（基础状态）和鞘内注药后5、30、60、120和240min时计算最大抗伤害效应百分比（MPE），测定机械缩足阈值（PWT），并进行倾斜板实验。于鞘内注药后第2周，取脊髓组织进行病理学观察，计算神经元异常率，行脊髓病理学评分和损伤分级。结果与R组比较，DR．组鞘内注药后30、60min时PWT升高，DR3组鞘内注药后120min时PWT降低（P〈0．05），DR2组各时点差异无统计学意义（P〉0．05），DR。组鞘内注药后5—240min时、DR2组鞘内注药后5和240min时、DR组鞘内注药后5min时MPE升高，DR。组鞘内注药后30、60rain时下滑角度降低（P〈0．05）；DR组与OR3组各时点上述指标差异无统计学意义（P〉0．05）；与c组比较，D凡组神经元异常率、脊髓病理学评分和损伤分级升高（P〈0．05），其余各组差异无统计学意义（P〉0．05）。结论右旋美托咪啶可增强0．5％罗哌卡因蛛网膜下腔阻滞的效果，且具有封顶效应。

Objective To investigate the effects of intrathecal （IT） dexmedetomidine on analgesia and neurotoxicity produced by ropivacaine spinal block. Methods Male SD rats weighing 250-300 g were used in this study. The animals were anesthetized with intraperitoneal 10% chloral hydrate 300 mg/kg. IT catheter was placed according to the technique described by Yaksh and Rudy. The tip of the IT catheter was positioned at lumbar region. Thirty-six SD rats in which IT catheter was successfully placed without complication were randomly allocated into 6 groups （ n = 6 each） ： group I received normal saline IT （ group C） ; group Ⅱ received 0.5 % ropivacaine 20 μlIT （group R） ; group m received dexmecletomidine 3 μg/kg IT （group D ） ; group Ⅳ, Ⅴ ,Ⅵ received 0.5% ropivacaine 20 μl ＋ dexmedetomidine 1, 2 and 3 μg/kg IT respectively （group DR1 , DR2, DR3 ） , Tail-flick test, paw withdrawal threshold to von frey stimuli and incline plate test were performed at 5, 30, 60, 120 and 240 min after IT drug administration. Two weeks later, the animals were sacrificed and the lumbar segment of the spinal cord was removed for microscopic examination. Results The duration of spinal block was significantly longer and the effect stronger in group DRl , DR2 and DR3 than in group R. Electron microscope showed that the injury to the myelin sheath of axon was the most severe in group DR3. Little or no damage to the axon was found in the other 5 groups （pathological score = 0）. Conclusion Dexmedetomidine IT can enhance spinal block produced by 0.5 % ropivacaine, and there is ceiling effect.