55 - An Anatomical Study to Define a Comprehensive Regional Nerve Block for Breast Cancer Surgery

Poster Board Number: 55
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Abstract Body : Introduction: Breast cancer is the most common cancer worldwide, with over 2.3 million new cases and 685,000 deaths in 2020 and a predicted increase to over 3 million new cases and 1 million deaths by 2040. Post-surgery, up to 60% of patients may experience chronic pain, a debilitating side effect that can negatively impact their quality of life. Acute pain, a significant risk factor for chronic pain development, can be managed by multimodal analgesia (MMA). The MMA approach combines several techniques, such as general and regional anesthesia, to treat pain and reduce opioid requirements. Importantly, quality pain management enhances post-operative recovery, decreases length of hospital stay, and reduces overall healthcare costs. Ultrasound guided interfascial nerve blocks are a recent advancement in regional anesthesia where local anesthetics are injected into targeted fascial planes, blocking the nerves traversing that plane. The well-known and documented serratus anterior plane block (SAPB) targets the intercostal nerves’ lateral cutaneous branches (LCBs), anesthetizing the breast laterally. The novel parasternal intercostal plane (PIP) block is reported to target the intercostal nerves’ anterior cutaneous branches (ACBs), anesthetizing the breast medially. The mechanism of interaction between these blocks is unknown, hence the current study proposes that combining SAPB and PIP would result in a comprehensive nerve block during breast surgery.

Methods: Four unembalmed cadavers (Western University, 3F, age = 60.5 ± 24.95yrs) with no history of upper body surgery were included. Injectates used were 20mL of diluted methylene blue (PIP) and 20mL of diluted India black ink (SAPB), each block performed bi-laterally (n=8). A high-frequency (6-13MHz) linear transducer aided ultrasound guided interfascial injection, undertaken at the 4th rib with a 22-gauge (80mm) echogenic needle advanced into the fascial plane deep to pectoralis major (PIP) and deep to serratus anterior (SAPB). Dissection of the area occurred 15 minutes post-injections (mimicking clinical practice), where the skin, sub-cutaneous tissue, pectoralis major and minor, and serratus anterior were reflected laterally to visualize dye spread within the planes. Staining of the LCBs and ACBs of intercostal nerves was measured by counting intercostal spaces where dye was observed, at the two injection sites.

Results: Injection of the SAPB stained the LCBs of intercostal nerves T2-T6 in 12.5% (1/8) of blocks, favouring the inferior T4-T6 in 75% (6/8) of blocks. Injection of the PIP stained ACBs of intercostal nerves T2-T4 in 75% (6/8) of blocks but failed to demonstrate spread from T2-T6. Surprisingly, staining of the medial and lateral pectoral nerves by the PIP was observed in 87.5% (7/8) of blocks.

Conclusion: Staining of intercostal nerves T2-T6, lateral pectoral, and medial pectoral nerves indicate a comprehensive nerve block to the breast when using the combined SAPB and PIP. Though historically known to be motor nerves, the medial and lateral pectoral nerves possess nociceptive afferent fibres, that when adequately blocked, may better aid in acute pain management.

Significance: Exploring the nature of dye diffusion of the interfascial SAPB and PIP blocks provides clinicians with precise anatomical evidence to translate the current research into future clinical trials for breast cancer surgery. Better pain management during surgery provides better quality of life for breast cancer survivors.