Median effective dose of 0.5% ropivacaine for ultrasound-guided femoral nerve block: dose 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 based on femoral nerve cross-sectional area for ultrasound-guided femoral nerve block. Methods:Patients of both sexes, aged 18-64 yr, of American Society of Anesthesiologists physical status I or Ⅱ, 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 enrolled in this study.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:Twenty-seven patients were enrolled in the study with the femoral nerve cross-sectional area (75±5) mm 2.ED 50 (95%CI) of 0.5% ropivacaine for ultrasound-guided femoral nerve block was 0.106 (0.069-0.125) ml/mm 2. Conclusion:ED 50 of 0.5% ropivacaine based on femoral nerve cross-sectional area for ultrasound-guided femoral nerve block is 0.106 ml/mm 2.