探讨罗哌卡因复合小剂量右美托咪定局部用药对其用于隐神经阻滞时半数有效浓度的影响。

拟行单侧膝关节置换术患者60例，年龄60～80岁，身体质量指数(BMI)<24 kg/m²，美国麻醉医师协会(ASA)分级Ⅰ～Ⅱ级。采用随机数字表法分为两组(n＝30)。超声引导下行隐神经阻滞，对照组神经阻滞时仅用罗哌卡因20 ml；复合药物组神经阻滞时注射罗哌卡因和0.8 μg/kg，右美托咪定混合液20 ml。罗哌卡因初始浓度为0.5%，采用序贯法确定下一例罗哌卡因浓度，相邻浓度比值为1.2；每隔5 min对患者进行视觉模拟评分法(VAS)评分评估阻滞效果。如本例患者有效，则下一例患者罗哌卡因浓度下调一个浓度梯度，反之则上调一级浓度。采用Dixon-Massey法确定罗哌卡因的半数效应浓度(EC₅₀)及其95%置信区间(CI)，并用U检验比较。其他资料比较采用t检验或卡方检验。

对照组罗哌卡因隐神经阻滞EC₅₀(95% CI)为0.45%(0.42%，0.46%)，复合药物组为0.34%(0.32%，0.36%)，复合药物组罗哌卡因EC50低于对照组(Z＝-3.219，P<0.05)。

罗哌卡因复合小剂量右美托咪定可显著降低罗哌卡因在隐神经阻滞的EC₅₀，对罗哌卡因隐神经阻滞产生显著的强化作用。

To evaluate effect of local application of small doses of dexmedetomidine on the medium effective concentration(EC50) of ropivacaine for saphenousnerve block and the mechanism of the analgesic effect induced by dexmedetomidine.

Forty-eight patients of American Society of Anesthesiologists (ASA) stageⅠtoⅡ, who were 60 to 80 years old with body mass index(BMI)<24 kg/m², were scheduled for elective unilateral total knee arthroplasty(TKA) under saphenousnerve block. They were randomly divided into two groups (30 cases each) using a random number table: the ropivacaine group and the combined drug group (ropivacaine mixed with 0.8 μg/kg dexmedetomidine). The volume of local anesthetics was 20 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. Visual analogue scale (VAS) was performed every five minutes to evaluate the block effect. 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. Median effect concentration (EC₅₀) and 95% confidence interval(CI) of ropivacaine were determined using the Dixon-Massey method, and compared by U test. Chi-square test and t test were also used.

The EC₅₀ (95% CI) of ropivacaine was 0.34%(0.32%, 0.36%)in the combined drug group and 0.45%(0.42%, 0.46%) in the ropivacaine group, which was significantly lower in the combined drug group than in the ropivacaine group (Z=-3.219, P<0.05).

Local application of small doses of dexmedetomidine can decrease EC₅₀ of ropivacaine for saphenousnerve block guided by ultrasound, enhance the efficacy of saphenousnerve block with ropivacaine.