Median effective dose of 0.375 ％ ropivacaine for ultrasound-guided subgluteus approach to the sciatic nerveblock in elderly patients

Objective To determine the median effective dose (ED50) of 0.375 ％ ropivacaine for ultrasound-guided subgluteus approach to the sciatic nerve block in the elderly patients.Methods Thirty ASA Ⅰ-Ⅲ patients of both sexes,aged 65-85 yr,scheduled for foot or ankle surgery under the sciatic nerve block,were enrolled in this study.The patients were placed in the Sim's position and received the sciatic nerve block using the posterior subgluteus approach guided by ultrasound.The initial dose of 0.375％ ropivacaine was 14.5 ml in the first patient and the ratio between the 2 successive doses was 1.2.The ED50 and 95 ％ confidence interval of ropivacaine were calculated by up-and-down technique.Results The ED50 and 95％ confidence interval of 0.375％ ropivacaine resulting in complete block of the sciatic nerve by using the ultrasound-guided subgluteus approach were 13.4 and 11.5-16.2 ml,respectively.Conclusion The ED50 of 0.375 ％ ropivacaine for ultrasound-guided subgluteus approach to the sciatic nerve block is 13.4 ml in the elderly patients. Key words: Amides; Sciatic nerve; Nerve block; Dose-response relationship, drug; Ultrasonography;  Aged