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\begin{document}

\title{the Median Effective Analgesic Concentration (MEAC) of Ropivacaine in
Ultrasound-Guided Interscalene Brachial Plexus Block for Postoperative
Analgesia after Proximal Humerus Fracture: A Double-Blind up-down
Concentration-Finding Study}



\author[1]{Yang Liu}%
\author[1]{Cheng Xu}%
\author[2]{Chengyu Wang}%
\author[1]{Fei Gu}%
\author[1]{Rui Chen}%
\author[3]{Quanhong Zhou}%
\author[3]{Jie Lu}%
\affil[1]{Shanghai Jiaotong University Affiliated Sixth People’s Hospital}%
\affil[2]{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.}%
\affil[3]{Affiliation not available}%


\vspace{-1em}



  
  \date{May 25, 2024}


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\selectlanguage{english}
\begin{abstract}
Background: This study aimed to determine the median effective analgesic
concentration of 10mL ropivacaine in interscalene brachial plexus block
for postoperative anesthesia in 50\% of the patients (EC50). Method:
This study was conducted on 30 patients with ASA grade I or II, who are
planning to undergo proximal humerus fracture operation. A concentration
of 10mL ropivacaine administered for the Interscalene brachial plexus
was determined using the up-and-down sequential. The initial
concentration of ropivacaine in the first patient to receive
interscalene brachial plexus block(ISBPB) was 0.3\%, After a successful
or unsuccessful postoperative analgesia, the concentration of local
anesthetic was decreased or increased, respectively, by 0.05\% in the
next patient. We defined successful postoperative analgesia as VAS score
below 4 at rest within initial 8 hours after ISBPB. 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 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 0.222\% (0.198\%, 0.335\%), 0.233\%
(0.215\%, 0.453\%), 0.223\% (0.202\%, 0.436\%), and 0.232\%,
respectively. Among all of the 4 models, the linear regression had the
least residual standard error (0.1676). 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 0.222\%--0.233\%.%
\end{abstract}%



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\textbf{Hosted file}

\verb`Table1 Patient Characteristic.docx`  available at \url{https://authorea.com/users/732466/articles/711843-the-median-effective-analgesic-concentration-meac-of-ropivacaine-in-ultrasound-guided-interscalene-brachial-plexus-block-for-postoperative-analgesia-after-proximal-humerus-fracture-a-double-blind-up-down-concentration-finding-study}

\textbf{Hosted file}

\verb`Table 2. The mean effective concentration and 95% confidence interval of the different models.docx`  available at \url{https://authorea.com/users/732466/articles/711843-the-median-effective-analgesic-concentration-meac-of-ropivacaine-in-ultrasound-guided-interscalene-brachial-plexus-block-for-postoperative-analgesia-after-proximal-humerus-fracture-a-double-blind-up-down-concentration-finding-study}

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