Fifty percent effective dosage of 0.5% ropivacaine for ultrasound guided subgluteal sciatic nerve blocking in elderly patients undergoing ankylosis arthrolysis of knee joint

Objective To determine the 50% effective dosage of 0.5% ropivacaine for ultrasound guided subgluteal sciatic nerve blocking in elderly patients undergoing ankylosis arthrolysis of knee joint.Methods Twenty-one ASA Ⅰ-Ⅲ elderly patients of both sexes,aged 65-79 year weighing 60-90 kg were recruited to receive ultrasound guided sciatic nerve blocking by means of subgluteal approach for ankylosis arthrolysis of knee joint.The volume of 0.5% ropivacaine was injected in each patient was based on modified Dixon's up-and-down method.The initial volume was 20 mL and each time the volume increased / decreased by 2 mL.The 50% effective dose and 95% confidence interval(95% CI) of 0.5% ropivacaine were calculated by using Probit Regression method.Results The median effective dosage of 0.5% ropivacaine for elderly patients undergoing ankylosis arthrolysis of knee joint by using of ultrasound guided sciatic nerve block with subgluteal approach is 14.5 mL(95% confidence interval 12.5-15.6 mL).Conclusion The 50% effective dosage of 0.5% ropivacaine for ultrasound guided subgluteal sciatic nerve block in elderly patients undergoing ankylosis arthrolysis of knee joint was 14.5 mL.