Determination of ECs0 of ropivacaine for postoperative analgesia under general anesthesia combined with single interscalene brachial plexus block / 临床麻醉学杂志

ABSTRACT

Objective To determine the 50％ minimum effective concentration (EC50) of ropivacaine for postoperative analgesia after shoulder arthroscopy under general anesthesia combined with interscalene brachial plexus block.Methods Patients undergoing selective shoulder arthroscopy were included in this study.There were 9 males and 13 females,BMI 18-28 kg/m2,falling into ASA physical status Ⅰ or Ⅱ.The interscalene brachial plexus block was achieved under the guidance of ultrasound and nerve stimulator at the level of C6.The upper trunk of interscalene brachial plexus was blocked with 5 ml ropivacaine.The concentration of ropivacaine intially was 0.5 ％ and then depended on the response of the previous patient's postoperative NRS scale.The target ropivacaine concentration was determined by up and down sequential method.The ratio of two consecutive ropiva caine was 1.2.Two termination conditions were,firstly,to achieve seven negative-positive up-anddown deflections required to calculate EC50,and secondly,to deriminate if 7 were positive outcomes using 5 ml of 0.1 ％ ropivacaine or 7 were negative outcomes using 5 ml of 1 ％ ropivaciane.EC50 and 95％CI of ropivacaine was calculated using the formula of Dixon-Massey sequential method.The incidence of hemidiaphragmatic paresis was evaluated.Pre-and post-operative pulmonary function was compared using paired t test.Results The EC50 of ropivacaine was 0.21％ (95 ％CI 0.18％-0.25 ％).The incidence of hemidiaphragmatic paresis was 9 cases(40.90％).Postoperative FVC and FEV1/FVC was significantly decreased than preoperative,but FEV1 (P =0.116) was not.Conclusion For patients undergoing shoulder arthroscopy under general anesthesia and interscalene brachial plexus block,the minimum effective concentration of ropivacaine for analgesia of EC50 is 0.21％,95％ CI 0.18％-0.25％.