Pectoralis I and II (Pecs I/Pecs II) blocks are modern regional anesthetic techniques performed in combination to anesthetize the nerves involved in breast surgery and axillary node dissection. Pecs II spread and clinical efficacy is thought to be independent of whether injection occurs between pectoralis minor and serratus anterior or deep to serratus anterior. Injecting deep to serratus anterior onto the rib may be technically easier; however, our clinical experience suggests that this approach may be less effective for axillary dissection. We undertook a cadaveric study to evaluate a subserratus plane approach for use in breast and axillary surgery.
Ultrasound-guided blocks using methylene blue dye were performed on 4 Genelyn-embalmed cadavers to assess and compare dye spread after a conventional Pecs II and a subserratus plane block at the third rib.
Conventional Pecs II injection demonstrated staining of the intercostobrachial nerve, third intercostal nerve, thoracodorsal nerve, long thoracic nerve, medial pectoral, and lateral pectoral nerve. The subserratus plane produced significantly less axillary spread, incomplete staining of the medial pectoral, and very minimal staining of the lateral pectoral nerve. Dye spread was limited to the lateral cutaneous branches of the intercostal nerves in both injections.
In our cadaveric study, injecting deep to serratus plane produced significantly less axillary spread. For breast surgery excluding the axilla, both techniques may be effective; however, for axillary dissection, the conventional Pecs II is likely to produce superior analgesia and additionally may help achieve complete coverage of the deeper pectoral nerve branches.