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

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250～300 g,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 μl;D组:鞘内注射右旋美托咪啶3 μg/kg 20 μl;R组:鞘内注射0.5%罗哌卡因20 μl;DR1组:鞘内注射右旋美托咪啶1 μg/kg+0.5%罗哌卡因20 μl;DR2组鞘内注射右旋美托咪啶2 μg/kg+0.5%罗哌卡因20 μl;DR3组鞘内注射右旋美托咪啶3 μg/kg+0.5%罗哌卡因20 μl.于鞘内注药前(基础状态)和鞘内注药后5、30、60、120和240 min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,DR1组鞘内注药后30、60 min时PWT升高,DR3组鞘内注药后120 min时PWT降低(P<0.05),DR2组各时点差异无统计学意义(P>0.05),DR1组鞘内注药后5～240 min时、DR2组鞘内注药后5和240 min时、DR3组鞘内注药后5 min时MPE升高,DR1组鞘内注药后30、60 min时下滑角度降低(P<0.05);DR2组与DR3组各时点上述指标差异无统计学意义(P>0.05);与C组比较,DR3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.

Effects of intrathecal dexmedetomidine on ropivacaine spinal block in rats

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 μl IT (group R); group Ⅲ received dexmedetomidine 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 yon 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 DR1, 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 celling effect.