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Cadaveric study investigating the phrenic-sparing volume for anterior suprascapular nerve block
  1. Naraporn Maikong1,
  2. Perada Kantakam1,
  3. Apichat Sinthubua1,
  4. Pasuk Mahakkanukrauh1,2,
  5. De Q Tran3 and
  6. Prangmalee Leurcharusmee2,4
  1. 1Department of Anatomy, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand
  2. 2Excellence in Osteology Research and Training Center (ORTC), Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand
  3. 3Department of Anesthesiology, St.Mary's Hospital, McGill University, Montreal, Quebec, Canada
  4. 4Department of Anesthesiology, Maharaj Nakorn Chiang Mai Hospital, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand
  1. Correspondence to Dr Prangmalee Leurcharusmee, Department of Anesthesiology, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand; prangmalee.l{at}cmu.ac.th

Abstract

Background This cadaveric study investigated the maximum effective volume of dye in 90% of cases (MEV90), required to stain the suprascapular nerve while sparing the phrenic nerve during the performance of an anterior suprascapular nerve block.

Methods In cadaveric neck specimens, using ultrasound guidance, the block needle was advanced until its tip was positioned underneath the omohyoid muscle next to the suprascapular nerve. The dye was injected in order to achieve circumferential spread around the latter. Successful phrenic-sparing suprascapular nerve block was defined as the non-staining of the phrenic nerve on dissection. Volume assignment was carried out using a Biased Coin Design, whereby the volume of dye administered to each cadaveric specimen depended on the response of the previous one. In case of failure (ie, stained phrenic nerve), the next one received a lower volume (defined as the previous volume with a decrement of 2 mL). If the previous cadaveric specimen had a successful block (ie, non-stained phrenic nerve), the next one was randomized to a higher volume (defined as the previous volume with an increment of 2 mL), with a probability of b=0.11, or the same volume, with a probability of 1 – b=0.89.

Results Thirty-one cadavers (56 cadaveric neck specimens) were included in the study. Using isotonic regression and bootstrap CI, the MEV90 for phrenic-sparing anterior suprascapular nerve block was estimated to be 4.2 mL (95% CI 3.0 to 5.0 mL). The probability of a successful response was estimated to be 0.90 (95% CI 0.84 to 0.96).

Conclusion For ultrasound-guided anterior suprascapular nerve block, the MEV90 of dye required to spare the phrenic nerve is 4.2 mL. Further studies are required to correlate this finding with the MEV90 of local anesthetic in live subjects.

  • nerve block
  • ultrasonography
  • upper extremity

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article.

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Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article.

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Footnotes

  • Contributors NM, PK, AS, PM, and PL participated in the planning, conception, design, conduct, reporting, acquisition of data, data analysis, and interpretation of data. DQT participated in the planning, conception, design, data analysis, and interpretation of data.

  • Funding This research received a grant from the Teacher Assistant or Research Assistant (TA/RA) Scholarship from the Graduate School of Chiang Mai University, and the Faculty of Medicine Research Fund (Grant No.014-2564) of Chiang Mai University, Chiang Mai, Thailand.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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