The median effective analgesic concentration (MEAC) of ropivacaine in
ultrasound-guided sciatic nerve block for postoperative analgesia after
ACL-R
Abstract
Background: The median effective concentration of ropivacaine of
ultrasound guided sciatic nerve block required for effective
postoperative analgesia after arthroscopic anterior cruciate ligament
reconstruction has not yet been determined. This study was to explore
the median effective analgesic concentration of ropivacaine required to
produce a successful sciatic nerve block for postoperative anesthesia.
Method: A total of 29 patients underwent elective arthroscopic anterior
cruciate ligament reconstruction were enrolled in study. A concentration
of 20mL ropivacaine administered for the sciatic nerve was determined
using the up-and-down sequential. The starting concentration was 0.2%
in the first patient, the next patient would receive decremented 0.025%
of ropivacaine if the prior patient’s postoperative visual analog pain
score was less than 4 in the initial 8h. Otherwise, the following
patient would received an incremental of 0.025% of ropivacaine. The
analytic techniques of linear, linear-logarithmic, exponential
regressions and centered isotonic regression were used to determine the
EC50 of ropivacaine. Results: The concentration of ropivacaine
administered ranged from 0.1% to 0.2%. The ED50 (95% confidence
interval) from 4 different statistical approaches (linear,
linear-logarithmic, exponential regressions and centred isotonic
regression) were 0.129% (0.103%, 0.359%), 0.142% (0.112%, 0.347%),
0.113% (0.108%, 0.343%), and 0.115%, respectively. Among all of the
4 models, the exponential regression had the least residual standard
error (0.2243). Conclusion: The EC50 derived from four statistical
models for 20ml ropivacaine in ultrasound-guided sciatic nerve block for
postoperative analgesia was distributed in a narrow range of
0.113%–0.142%, and the exponential regression was the model to best
match the study data