硬膜外注射右美托咪啶用于患者镇痛的适宜剂量

Appropriate dose of dexmedetomidine for epidural analgesia

目的比较不同剂量右美托咪啶对罗哌卡因硬膜外阻滞半数有效浓度（EC50）的影响，以探讨其硬膜外给药用于患者镇痛的适宜剂量。方法拟行膝关节镜诊治术患者120例，年龄20-55岁，体重50—75kg，ASA分级I级，采用随机数字表法，将其随机分为4组（n=30）。Do组：硬膜外注射罗哌卡因20ml；Do25组、D0.50组和D1．00组分别硬膜外注射罗哌卡因混合液含0．25、0．50和1．00ug／kg右美托咪啶。硬膜外注射罗哌卡因混合右美托咪啶的容量为20ml。D0组、D0.25组、D0.50组或D1.00组首例罗哌卡因浓度分别为0．40％、0．40％、0．28％和0．20％，按照序贯法调整罗派卡因浓度，升降幅度为0．02％。采用VAS评价对手术切皮的阻滞效果，VAS评分=0分为阻滞有效。采用概率单位法计算罗哌卡因EC50及其95％可信区间（95％CI）。记录有关不良反应的发生情况。结果砜组、D0.25组、D0.50组和D1.00组罗哌卡因EC50及95％CI分别为0．38％（0．35～0．41）％、0．34％（0．31～0．36）％、0．22％（0．20～0．24）％和0．14％（0．12～0．15）％。D0组、D0．25组、D0.50组、D1.00组罗哌卡因EC50依次降低（P〈0．05）；与D0组比较，D1.00组低血压和心动过缓的发生率升高（P〈0．05），D0.25组和D0.50组不良反应发生率差异无统计学意义（P〉0．05）。结论硬膜外注射右美托咪啶用于患者镇痛的适宜剂量为0．50ug／kg。

Objective To compare the effects Of different doses of dexmedetomidine on the median effective concentration （EC50） of ropivacaine for epidural block and investigate the appropriate dose. Methods One hundred and twenty ASA I patients of both sexes, aged 20-55 yr, weighing 50-75 kg, scheduled for knee arthro- scopic operation, were randomly divided into 4 groups （ n = 30 each） ： no dexmedetomidine group （group D0 ）, 0.25 ug/kg dexmedetomidine group （group D0.25 ）, 0.50ug/kg dexmedetomidine group （ group D0.50 ）, and 1.00 ug/kg dexmedetomidine group （group Dl.oo ）. In group Do, ropivacaine 20 ml was injected into epidural space. The ropivacaine-dexmedetomidine mixtures containing 0.25, 0.50 and 1.00ug/kg dexmedetomidine were injected into epidural space in groups D0.25, D1.00 and Do.so respectively. The volume of mixtures was 20 ml in groups D0.25, D1.00 and D0.50. The initial concentration of ropivacaine was set at 0.40% , 0.40% , 0.28% and 0.20% in groups D0, D0.25 , D0.50 and D1.00 respectively and then the EC50 was determined by up-and-down technique. The concentra- tion of ropivacaine was increased/decreased by 0.02 % in the next patient. The analgesic effect was assessed using VAS score. VAS score = 0 was considered as effective analgesia. The ECso and 95 % confidence interval （CI） of ropivacaine were calculated using probit method. Adverse effects were recorded. Results The EC50 and 95 % CI of ropivaeaine was 0.38% （0.35-0.41）%, 0.34% （0.31-0.36）%, 0.22% （0.20-0.24）% and 0.14% （0.12-0.15） % in groups D0 , D0.25, D0.50 and D1.00 respectively. The ECso of ropivacaine was decreased gradually in groups D0 , D0.25 , D0.50 and D1.00 （ P 〈 0.05）. Compared with group Do , the incidence of hypotension and bradycardia was significantly increased in group D1.00 （P 〈 0.05）, while no significant change was found in the incidence of adverse effects in groups D0.25 and D0.50 （P 〉 0.05）. Conclusion The appropriate dose of dexmedetomidine for epidural analgesia is 0.50ug/kg.