Comparison of Serratus Posterior Superior Intercostal Plane Block and Pectoral Nerve Block II for Postoperative Analgesia Following Modified Radical Mastectomy: A Retrospective Cohort Study

Background/Objectives: To compare the postoperative analgesic efficacy of the serratus posterior superior intercostal plane (SPSIP) block and pectoral nerve block II (PECS II) in patients undergoing unilateral modified radical mastectomy (MRM). Methods: This single-center retrospective cohort study included 100 patients who underwent unilateral MRM and received either an SPSIP block (n = 34) or a PECS II block (n = 66). The primary outcome was the time from extubation to the first administration of rescue analgesia. Secondary outcomes included Numeric Rating Scale (NRS) pain scores at 1, 4, 8, and 12 h postoperatively, the maximum NRS pain score, and cumulative opioid consumption within the first 24 postoperative hours. The primary outcome was analyzed using a generalized linear model with a gamma distribution and log-link function adjusted for operative duration. A sensitivity analysis additionally adjusted for age, body mass index, American Society of Anesthesiologists (ASA) physical status, and smoking status. Results: Among 100 patients (SPSIP, n = 34; PECS II, n = 66), operative duration was longer in the PECS II group (p < 0.001). Time to first rescue analgesia was longer with SPSIP (7.5 [5.0–8.8] vs. 5.0 [3.0–8.0] h; p = 0.004), but the difference was not significant after adjustment for operative duration (exp(B) = 1.21, 95% CI 0.98–1.49; p = 0.077) or additional covariates (exp(B) = 1.17, 95% CI 0.94–1.46; p = 0.153). NRS scores were lower with SPSIP at 1 h (p < 0.001) and with PECS II at 8 and 12 h (Holm-adjusted p = 0.013 and p < 0.001). Twenty-four-hour tramadol consumption was similar (p = 0.922). No block-related complications were documented. Conclusions: After adjustment for operative duration, the longer time to first rescue analgesia observed in the SPSIP group did not retain statistical significance, and a similar result was obtained in the sensitivity analysis. The findings should be interpreted cautiously in view of the retrospective design and limited sample size.