The Median Effective Analgesic Concentration (MEAC) of Ropivacaine in
Ultrasound-Guided Interscalene Brachial Plexus Block for Postoperative
Analgesia after Arthroscopic Repair of Rotator Cuff: A Double-Blind
Up-Down Concentration-Finding Study
Chengyu Wang
Department of Anesthesiology, Perioperative and Pain Medicine, The Second Affiliated Hospital and Yuying Children’s Hospital of Wenzhou Medical University;Key Laboratory of Anesthesiology of Zhejiang Province, The Second Affiliated Hospital and Yuying Children’s Hospital of Wenzhou Medical University, 325000, Zhejiang, China.
Author ProfileAbstract
Objectives:The median effective concentration of ropivacaine in
interscalene brachial plexus block for postoperative analgesia after
arthroscopic rotator cuff repair(ARCR) has not been determined. Design:
this is a prospective double blinded study. Method: This study was
conducted on 40 patients with ASA grade I or II who had selective ARCR.
A concentration of 10mL ropivacaine administered for the Interscalene
brachial plexus block(ISBPB) was determined using the up-and-down
sequential. The initial concentration of ropivacaine 0.3%. After a
successful or unsuccessful postoperative analgesia, the concentration of
ropivacaine was decreased or increased by 0.05% in the next patient,
respectively. We defined successful postoperative analgesia as a visual
analogue scale(VAS)score<4 at rest or activity within initial 8 hours
after ISBPB. VAS score≥4 was defined as unsuccessful analgesia. The
analytic techniques of linear, linear-logarithmic, exponential
regressions and centered isotonic regression were used to determine the
EC50 of ropivacaine and the residual standard errors were calculated for
the comparison of “goodness of fit” among the different models.
Results: The concentration of local anesthetic ropivacaine administered
ranged from 0.1% to 0.35%. The EC50 (95% confidence interval) from 4
different statistical approaches (linear, linear-logarithmic,
exponential regressions and centred isotonic regression) were 0.207%
(0.168%, 0.355%), 0.182% (0.165%, 0.353%), 0.196% (0.154%,
0.356%), and 0.163%, respectively. Among all of the 4 models, the
exponential regression had the least residual standard error (0.0990).
Conclusion: The EC50 derived from four statistical models for 10ml
ropivacaine in ultrasound-guided interscalene brachial plexus block for
postoperative analgesia was distributed in a narrow range of
0.163%–0.207%.