Spread of Injectate After Combined Deep Serratus Anterior and Superficial Parasternal Intercostal Plane Injections: A Cadaver Study to Evaluate Their Utility in Breast Surgery

Abstract

Background: Analgesia for breast surgery by a single peripheral nerve block is challenging as breast tissue receives innervation from multiple sources. In this cadaveric study, we evaluated the injectate spread of combined superficial parasternal intercostal plane (PIP) and deep serratus anterior plane (SAP) injections in the tissues relevant for breast surgery analgesia. Methods: We performed ultrasound-guided dye injections in 18 hemithoraces. 20 mL of methylene blue solution was injected into the superficial PIP at the fourth rib. Following that, 20 mL of black India Ink solution was injected in the SAP at the fourth rib at the midaxillary line. We dissected the specimens, 15 min post-injection to visualize dye dispersion. Staining of the intercostal nerves from each injection was measured by counting the number of intercostal spaces and nerves stained. Results: For PIP injections, the cranial spread of injectate was observed up to the second intercostal nerve involving the anterior cutaneous branch in 14/16 (87.5%) with caudal spread to the fifth intercostal nerve in 15/16 (94%). In addition, the staining of the medial and lateral pectoral nerves was noted in 14/16 (88%) of the specimens. For the SAP dye injections, the cranial spread of injectate was observed up to the lateral cutaneous branch of the third intercostal nerve level in 9/16 (56%) of specimens and caudal spread up to the lateral cutaneous branch of the sixth intercostal nerve in 14/16 (88%) specimens. Conclusions: This study demonstrated extensive spread of dye injectate with combined PIP and SAP injections involving anterior and lateral cutaneous branches of intercostal nerves and lateral and medial pectoral nerves. This study demonstrates an alternative analgesic approach to provide perioperative analgesia for breast surgery. Editorial Comment: This cadaver study demonstrates that combining deep serratus anterior block with parasternal intercostal plane block provides reliable injectate spread to the cutaneous branches of intercostal nerves. In a clinical setting, this could provide comprehensive analgesia for the breast. Compared with paravertebral blocks, the combination of two fascial plane blocks may offer a technically less challenging alternative with a lower risk of complications.