Comparison of ultrasound-guided serratus posterior superior intercostal plane block and thoracic paravertebral block for postoperative analgesia after breast surgery: a prospective randomized noninferiority trial.

Background/aim: This noninferiority trial aimed to evaluate whether the serratus posterior superior intercostal plane block (SPSIPB) provides noninferior postoperative analgesia compared with the thoracic paravertebral block (TPVB) after unilateral mastectomy. Materials and methods: This prospective, randomized, assessor-blinded, parallel-group noninferiority trial enrolled 60 female patients scheduled for elective unilateral mastectomy. Patients received either ultrasound-guided SPSIPB (n = 30) or TPVB (n = 30) with 30 mL of 0.25% bupivacaine before induction. The primary outcome was visual analogue scale (VAS) pain scores (0-100 mm) at rest and during coughing over 24 h. Noninferiority was assessed using the Hodges-Lehmann median difference with 95% confidence intervals (CIs) and a prespecified margin of 13 mm, corresponding to the validated minimal clinically important difference (MCID). Secondary outcomes included opioid consumption, area under the curve (AUC) for cumulative pain burden, and patient satisfaction. Results: All 60 patients completed the study. At the first postoperative hour, TPVB provided lower VAS scores at rest (median 10.0 vs. 23.0 mm, 95% CI of difference: 0 to 19). For resting VAS, noninferiority was demonstrated at 0 h, 4 h, and 24 h (upper bounds: 11.5 mm, 12.5 mm, and 5.0 mm). The 24-h AUC for resting VAS was comparable between groups (426 mm/h vs. 426.5 mm/h, p = 0.652). SPSIPB produced significantly lower tramadol consumption in the 12-to-24-h interval (median 0 vs. 50 mg, p < 0.001). However, total opioid consumption over the 24 h was comparable (p = 0.070). No block-related complications occurred in either group. Conclusion: Noninferiority of SPSIPB to TPVB was demonstrated for resting pain scores at the majority of postoperative time points after unilateral mastectomy. TPVB provided a transient early-phase analgesic advantage at 1 h and 2 h, while SPSIPB was associated with late-phase opioid sparing. The comparable cumulative pain burden across 24 h suggests that SPSIPB may serve as a periparavertebral alternative to TPVB when sustained analgesia and opioid reduction are clinical priorities.