Median effective dose of 0.5% ropivacaine for ultrasound-guided femoral nerve block when combined with dexmedetomidine: dose based on per unit femoral nerve cross-sectional area / 中华麻醉学杂志

ABSTRACT

Objective:To determine the median effective dose (ED 50) of 0.5% ropivacaine when combined with dexmedetomidine based on femoral nerve cross-sectional area for ultrasound-guided femoral nerve block. Methods:American Society of Anesthesiologists physical statusⅠor Ⅱ patients of both sexes, aged 18-64 yr, with body mass index of 20-30 kg/m 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 50 was determined by Dixon′ s up-and-down sequential method.The initial dose was 0.22 ml/mm 2, and the difference between the two successive doses was 0.02 ml/mm 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.ED 50 and 95% confidence interval (CI) were calculated using Probit analysis. Results:In group R, 27 patients were enrolled in the study, and ED 50 (95%CI) of 0.5% ropivacaine for ultrasound-guided femoral nerve block was 0.106 (0.069-0.125) ml/mm 2.In group DR, 23 patients were enrolled in the study, and ED 50 (95% CI) of 0.5% ropivacaine for ultrasound-guided femoral nerve block was 0.038 (0.011-0.059) ml/mm 2.Compared with group R, ED 50 of 0.5% ropivacaine for femoral nerve block was significantly decreased in group R. Conclusion:When combined with dexmedetomidine 0.5 μg/kg, ED 50 of 0.5% ropivacaine based on femoral nerve cross-sectional area for ultrasound-guided femoral nerve block is 0.038 ml/mm 2.