Determination of minimal motor-blocking local analgesic concentration of epidural ropivacaine in the postoperative analgesia

Objective The aim of this study was to determine the minimal motor-blocking concentration of epidural ropivacaine in the postoperative epidural analgesia.Methods Thirty ASA I women who underwent gynaecologic operation and requested epidural analgesia were enrolled in the study.Epidural catheter was placed at L2-3 and advanced for 3cm in the epidural space in a cephalad direction.Each received a 10 ml bolus of epidural ropivacaine.The first woman received 0.660%.Up-down sequential allocation was used to determine subsequent concentration: to increase the concentration by one level if the previous woman did not respond and to reduce the concentration by one leve1 if the previous woman did respond.The up down sequences were analyzed by using the Brownlee method to quantify the minimal motor-blocking local analgesic concentration.TWO-sided P0.05 was defined as significance.Results The minimal motor-blocking concentration of epidural ropivacaine in the post-operative epidural analgesia was 0.706%(95%confidence interval,0.6852% ～ 0.7272%).Conclusion The minimal motor-blocking local analgesic concentration of ropivacaine quantified in this study is a theoretic guideline for the clinical use of ropivacaine in the post-operative epidural analgesia.