Appropriate dose of dexmedetomidine for epidural analgesia / 中华麻醉学杂志

ABSTRACT

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 arthroscopic operation,were randomly divided into 4 groups (n =30 each)no dexmedetomidine group (group D0),0.25 μg/kg dexmedetomidine group (group D0.25),0.50μg/kg dexmedetomidine group (group D0.50),and 1.00μg/kg dexmedetomidine group (group D1.00).In group D0,ropivacaine 20 ml was injected into epidural space.The ropivacaine-dexmedetomidine mixtures containing 0.25,0.50 and 1.00 μg/kg dexmedetomidine were injected into epidural space in groups D0.25,D1.00 and D0.50 respectively.The volume of mixtures was 20 nl 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 concentration 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 EC50 and 95％ confidence interval (CI) of ropivacaine were calculated using probit method.Adverse effects were recorded.Results The EC50 and 95 ％ CI of ropivacaine 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 EC50 of ropivacaine was decreased gradually in groups D0,D0.25,D0.50 and D1.00 ( P ＜ 0.05).Compared with group D0,the incidonce 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 0.50 μg/kg.