不同剂量右美托咪定对罗哌卡因臂丛神经阻滞时半数有效浓度的影响

Effects of different doses of dexmedetomidine on median effective concentration of ropivacaine for brachial plexus block

目的通过评价不同剂量右美托咪定对罗哌卡因用于臂丛神经阻滞时半数有效浓度（EC50）的影响，确定右美托咪定局部用药的适宜剂量。方法择期行尺骨和桡骨骨折切开复位内固定术的患者，性别不限，年龄19～50岁，体重50～80kg，ASA分级I或Ⅱ级，拟在超声引导下行腋路臂丛神经阻滞。采用随机数字表法，将其分为4组：对照组（C组）、右美托咪定0．4、O．6、0．8μg／kg组（D．组、D：组和D，组），C组神经阻滞用药仅为罗哌卡因，D1-3组神经阻滞用药为罗哌卡因和相应剂量右美托咪定的混合液。以臂丛支配区痛觉消失作为阻滞有效的标准，局麻药容量为40ml，采用序贯法确定罗哌卡因浓度，初始浓度为0．4％，相邻浓度的比值为1．0，阻滞有效时采用低一级浓度，否则采用高一级浓度，直至每组出现第7个交叉点。以各交叉点罗哌卡因浓度的均数作为罗哌卡因用于臂丛神经阻滞的EC50。记录臂丛神经阻滞有关不良事件、心血管不良事件和镇静过度的发生情况。结果C组、D1组、D2组和D3组入选病例分别为20、22、24、19例；与C组比较，D2组和D3组罗哌卡因用于臂丛神经阻滞的EC50降低（P〈0．05），D1组罗哌卡因用于臂丛神经阻滞的EC50差异无统计学意义（P〉O．05）。D1组未见不良事件发生，D2组心动过缓发生率为17％，但是一过性的；D3组心动过缓发生率为58％，低血压发生率为32％，且需要特殊处理，镇静过度发生率为10％。结论混合罗哌卡因用于臂丛神经阻滞时右美托咪定的适宜剂量为0．6μg／kg。

Objective To determine the optimum dose of dexmedetomidine administered locally through evaluating the effects of different doses of dexmedetomidine on the median effective concentration （ECs0） of ropivaeaine for braehial plexus block. Methods American Society of Anesthesiologists physical status I or II patients of both sexes, aged 19-50 yr, weighing 50-80 kg, scheduled for elective ulna and radius fracture open reduction and internal fixation, requiring ultrasound-guided axillary braehial plexus block, were randomly assigned into 4 groups using a random number table： control group （group C） and dexmedetomidine 0.4, 0.6 and 0.8 μg/kg groups （D1, D2 and Ds groups）. Axillary brachial plexus block was performed only with ropivaeaine in group C. In D1-3 groups, axillary braehial plexus bloek was performed with the mixture of ropivaeaine and dexmedetomidine 0.4, 0.6 and 0.8 μg/kg, respectively. The effective block was defined as complete loss of pain sensation in the areas innervated by the braehial plexus. The volume of local anesthetics was 40 ml. The concentration of ropivacaine was determined by up-and-down technique. The initial concentration was 0.4% and the ratio between the two successive concentrations was 1.0. If the block was effective, the next patient received a lower dose of ropivacaine; or conversely if ineffective, a higher dose was given in the next patient. At least 7 independent crossover pairs were observed in each group. The EC50 of ropivacaine was the mean of the concentration of ropivacaine of each crossover pair. The occurrence of brachial plexus block-related adverse events, adverse cardiovascular events and over-sedation was recorded. Results In C, D1, D2 and D3 groups, 20, 22, 24 and 19 patients were enrolled, respectively. Compared with group C, the EC50 of ropivacaine was significantly decreased in D2 and D3 groups, and no significant change in the EC50 of ropivacaine was found in group D1. No patients developed adverse events in group D1. The incidence of bradycardia was 17%, but it was transient in group D2. In group D3 , the incidence of bradycardia and hypotension was 58% and 32%, respectively, and they required special treatment, and the incidence of over-sedation was 10%. Conclusion The optimum dose of dexmedetomidine is 0.6 μg/kg when mixed with ropivacaine for brachial plexus block.