Serratus Plane Block: A Cadaveric Study to Evaluate Optimal Injectate Spread

Background and Objectives Although serratus plane block reportedly provides satisfactory analgesia for breast and thoracic surgeries, the optimal technique for consistent success has not been studied. The goal of this anatomical study was to evaluate the impact of volume, level, and site of injection on the extent of injectate spread that can influence anesthetic coverage. Methods Ultrasound-guided dye injection and subsequent dissection were performed in 39 cadaveric hemithoraces. Methylene blue was injected according to 1 of 4 injection protocols as follows: one 20-mL bolus, either superficial or deep to the serratus anterior muscle (SAM), at the fifth rib level (groups SUP-20 and DEEP-20, respectively), or two 20-mL boluses, either superior or deep to the SAM, one at the third rib and one at the fifth rib level (group SUP-40 and group DEEP-40, respectively). Following injection, dissection and 3-dimensional digitization were performed to map the area of dye spread. Results We found that the extent of dye spread was mostly influenced by the volume of injection rather than the plane of injection (superficial vs deep to SAM). Increasing the volume from 20 to 40 mL doubled the area of injectate spread and promoted dye spread preferentially to the anterior chest wall, with some impact on cephalad-to-caudad spread and no impact on posterior spread. Dye was found most consistently in the axilla when a separate injection was performed at the third rib level. Conclusions Our data showed that a high-volume double-injection technique provides extensive and consistent dye spread in the anterior chest wall and axilla, regardless of the plane of injection relative to the SAM. This technique likely provides more reliable analgesic coverage for breast procedures especially those that involve the axilla, pending confirmation in future clinical studies. Accepted for publication April 22, 2018. Address correspondence to: Vincent Chan, MD, FRCPC, FRCA, Department of Anesthesia, Toronto Western Hospital, University Health Network, University of Toronto, 399 Bathurst St, MCL 2-405, Toronto, Ontario M5T 2S8, Canada (e-mail: vincent.chan@uhn.ca). V.C. has received honorarium from SonoSite, BBraun, and Aspen Pharma. He also sat on the Medical Advisory Board of Smiths Medical. A.P. has a research grant from Fisher and Pykel for an unrelated study. She is associate editor of Regional Anesthesia and Pain Medicine. A.A. is an anatomy faculty at Allergan Academy of Excellence. The other authors declare no conflict of interest. Copyright © 2018 by American Society of Regional Anesthesia and Pain Medicine.

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