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目的:确定混合右美托咪定时0.5%罗哌卡因用于超声引导股神经阻滞按股神经横截面积用药的EDn 50 。n 方法:选择行髌骨骨折切开复位内固定术或髌骨骨折内固定取出术患者，ASA分级Ⅰ或Ⅱ级，BMI 20~30 kg/mn 2，年龄18~64岁，性别不限，采用随机数字表法分为右美托咪定+罗哌卡因组(DR组)和罗哌卡因组(R组)。DR组注射0.5%罗哌卡因+右美托咪定0.5 μg/kg，R组注射0.5%罗哌卡因。超声引导下定位股神经，测量股神经横截面积，根据股神经横截面积注入0.5%罗哌卡因，采用Dixon序贯法进行试验，起始剂量为0.22 ml/mmn 2，相邻剂量差值为0.02 ml/mmn 2。阻滞有效标准：神经阻滞30 min内膝关节前侧皮肤、小腿内侧面和足背内侧缘皮肤均无痛觉和Brunnstrom运动功能评定法为1~3期。若以上神经分布区有1处存在痛觉即认为神经阻滞无效。出现7个有效和无效交替波终止研究。采用Probit法计算EDn 50及其95%可信区间(CI)。n 结果:R组27例患者纳入研究，0.5%罗哌卡因股神经阻滞EDn 50为0.106 ml/mmn 2，95%CI为0.069~0.125 ml/mmn 2。DR组23例患者纳入研究，0.5%罗哌卡因股神经阻滞EDn 50为0.038 ml/mmn 2，95%CI为0.011~0.059 ml/mmn 2。与R组比较，DR组0.5%罗哌卡因股神经阻滞EDn 50降低(n P<0.05)。n 结论:混合右美托咪定0.5 μg/kg时，0.5%罗哌卡因用于超声引导股神经阻滞的按股神经横截面积用药EDn 50为0.038 ml/mmn 2。n “,”Objective:To determine the median effective dose (EDn 50) of 0.5% ropivacaine when combined with dexmedetomidine based on femoral nerve cross-sectional area for ultrasound-guided femoral nerve block.n Methods:American Society of Anesthesiologists physical statusⅠor Ⅱ patients of both sexes, aged 18-64 yr, with body mass index of 20-30 kg/mn 2, scheduled for elective open reduction and internal fixation for patella fracture or removal of patella fracture by internal fixation, were randomly divided into dexmedetomidine and ropivacaine group (group DR) and ropivacaine group (group R). In group DR, 0.5% ropivacaine and 0.5 μg/kg dexmedetomidine were injected.In group R, 0.5% ropivacaine was injected.Ultrasonic localization of femoral nerve was performed for measurement of the femoral nerve cross-sectional area, and 0.5% ropivacaine was injected based on the area.ED n 50 was determined by Dixon′ s up-and-down sequential method.The initial dose was 0.22 ml/mmn 2, and the difference between the two successive doses was 0.02 ml/mmn 2.The effective block was defined as complete loss of pain sensation in the areas of anterior skin of knee joint, skin on the inner side of the calf and dorsal medial skin of the foot and the degree of motor block was in stages 1-3 assessed using Brunnstrom motor function within 30 min after nerve block.Nerve block was considered ineffective if pain occurred in any nerve distribution area mentioned above.The study was terminated if 7 effective and ineffective alternating waves occurred.EDn 50 and 95% confidence interval (CI) were calculated using Probit analysis.n Results:In group R, 27 patients were enrolled in the study, and EDn 50 (95%CI) of 0.5% ropivacaine for ultrasound-guided femoral nerve block was 0.106 (0.069-0.125) ml/mmn 2.In group DR, 23 patients were enrolled in the study, and EDn 50 (95% CI) of 0.5% ropivacaine for ultrasound-guided femoral nerve block was 0.038 (0.011-0.059) ml/mmn 2.Compared with group R, EDn 50 of 0.5% ropivacaine for femoral nerve block was significantly decreased in group R.n Conclusion:When combined with dexmedetomidine 0.5 μg/kg, ED n 50 of 0.5% ropivacaine based on femoral nerve cross-sectional area for ultrasound-guided femoral nerve block is 0.038 ml/mmn 2.n