Interpectoral and serratus anterior plane blocks in mastectomy: unravelling the disconnect between acute and chronic pain

We read with interest the randomised controlled trial by Kono et al., who investigated the combination of interpectoral plane and superficial serratus anterior plane blocks for the prevention of postmastectomy pain [1]. We congratulate the authors on their rigorous study design, particularly the blinding of the proceduralists, which adds significant value to the existing literature on chest wall blocks. However, three aspects of the results warrant further discussion regarding their physiological plausibility and clinical interpretation. The prevailing theory of persistent postsurgical pain suggests that effective control of early nociceptive input is a key mechanism in preventing central sensitisation and the transition to chronic pain [2]. Yet, in this study, the intervention did not reduce acute pain intensity at 2 h or 24 h nor did it reduce opioid consumption compared with the control group. If the afferent blockade was insufficient to alter acute pain trajectory, the mechanism for the reported reduction in chronic pain at 6 months is unclear. This effect could be attributed to the systemic absorption of the larger total volume of ropivacaine in the intervention group acting on anti-inflammatory pathways, rather than a direct neural blockade effect. Clarifying this mechanism is crucial for replicating these results in clinical practice. We noted a divergence between the intention-to-treat and per-protocol analyses. While the primary outcome in the intention-to-treat analysis reached statistical significance (p = 0.044), the per-protocol analysis, which excluded three protocol violations, did not (p = 0.069). This shift suggests that the statistical significance of the primary finding is somewhat fragile. As highlighted in recent systematic reviews of anaesthesiology trials, statistically significant findings with p values near 0.05 can be sensitive to minor variations in event rates or protocol adherence [3]. We suggest that these results be interpreted with caution until validated by a larger cohort. Finally, the clinical relevance of the difference in chronic pain incidence deserves reflection. The primary outcome was defined as any pain (numeric rating scale > 0). Although fewer patients in the intervention group reported pain (18% vs. 38%), the median pain scores at 6 months were 0 in both groups, and pain intensity with movement was also clinically indistinguishable. Given that the minimum clinically important difference for pain reduction is often cited as approximately 10–20 mm on a 100-mm scale or one to two points on a numeric rating scale [4], distinguishing between a pain-free patient and one with negligible pain may have limited impact on quality of life, especially since no patient required analgesics. Future studies might benefit from focusing on moderate to severe pain or functional impairment as primary endpoints to better capture patient-centred benefits.