摘要目的 通过评价右美托咪定局部用药对罗哌卡因臂丛神经阻滞半数有效浓度(EC50)的影响,探讨其局部用药的镇痛机制.方法 前臂及手部择期手术患者52例,年龄18 ～ 50岁,体重50～80 kg,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2组(n=26),对照组(C组)神经阻滞时仅用罗哌卡因；右美托咪定组(D组)神经阻滞时局部注射罗哌卡因和0.8 μg/kg右美托咪定的混合液.以臂丛支配区痛觉消失为阻滞有效,局麻药容量30 ml,采用序贯法确定罗哌卡因浓度:初始浓度为0.50％,相邻浓度比值为1.2,阻滞有效则下一例采用低一级浓度,阻滞无效则下一例采用高一级浓度.用Dixon-Massey法确定EC50及其95％可信区间.结果 D组罗哌卡因EC50(95％可信区间)为0.32％ (0.30％ ～ 0.33％),C组为0.44％ (0.42％ ～ 0.46％).D组罗哌卡因EC50低于C组(P＜0.05).结论 右美托咪定局部用药可降低罗哌卡因臂丛神经阻滞的EC50,提示其具有局麻药样效应.

abstractsObjective To investigate effect of local application of dexmedetomidine on the medium effective concentration (EC50) of ropivacaine for brachial plexus block and the mechanism of the analgesic effect induced by dexmedetomidine.Methods Fifty-two ASA Ⅰ or Ⅱ patients of both sexes,aged 18-50 yr,weighing 50-80 kg,scheduled for elective forearm or hand surgery,requiring ultrasound-guided axillary brachial plexus block,were randomly assigned into 2 groups (n =26 each):control group (group C) and dexmedetomidine group (group D).Axillary brachial plexus block was performed using only ropivacaine in group C.In group D the mixture of ropivacaine and 0.8 μg/kg dexmedetomidine was injected for the block.The effective block was defined as complete loss of pain sensation in the brachial plexus distribution.The volume of local anesthetics was 30 ml.The concentration of ropivacaine was determined by up-and-down technique.The initial concentration was 0.5 ％ and the ratio between the two successive concentrations was 1.2.If the block was effective,the next patient received a lower dose of ropivacaine,or if ineffective,a higher dose was given in the next patient.The EC50 and 95 ％ confidence interval of ropivacaine were determined using the Dixon-Massey method.Results The EC50 (95 ％ confidence interval) of ropivacaine was 0.32％ (0.30％-0.33％) in group D and 0.44％ (0.42％-0.46％) in group C.The EC50 of ropivacaine was significantly lower in group D than in group C (P ＜ 0.05).Conclusion Local application of dexmedetomidine can decrease the EC50 of ropivacaine for brachial plexus block guided by ultrasound,indicating that the mechanism of the analgesic effect induced by dexmedetomidine is related to the local anesthetic-like effect.