Retro-SCTL Space Block vs Rhomboid Intercostal Block for Analgesia After Modified Radical Mastectomy

Patients will be randomized 1:1 to retro-SCTLS block at T3-T4 or RIB at T5-T6, using a computer-generated sequence with variable block sizes and sequentially numbered opaque sealed envelopes. To maintain blinding, both regions will be scanned in all patients and identical dressings applied at both sites. Sensory block (cold testing, T1-T6 and axilla) will be assessed 30 minutes after injection by a blinded assessor. General anesthesia and postoperative multimodal analgesia are standardized: paracetamol 1 g IV every 6 h and ketorolac 30 mg IV every 12 h, with rescue morphine 2 mg IV for NRS ≥ 4. The primary analysis is intention-to-treat using the Mann-Whitney U test, with the Hodges-Lehmann median difference and 95% CI. Assuming a 2 mg difference and a conservative SD of 3.1 mg (two-sided α 0.05, 80% power), 39 patients per group are required; 44 per group (88 total) will be enrolled to allow for 10% dropout.

Ultrasound-guided retro superior costotransverse ligament space block at T3-T4 with 20 mL of 0.25% bupivacaine, before induction under dexmedetomidine sedation.

Procedure: Retro Superior Costotransverse Ligament Space Block

Ultrasound-guided RIB at T5-T6 with 20 mL of 0.25% bupivacaine, before induction under dexmedetomidine sedation.

Procedure: Rhomboid Intercostal Block

Single-injection block at T3-T4 under ultrasound guidance, with 20 mL of 0.25% bupivacaine injected into the space posterior to the superior costotransverse ligament. It is performed before general anesthesia under standardized dexmedetomidine sedation (0.5 mcg/kg load, then 0.3 mcg/kg/h).

Single-injection block at T5-T6 under ultrasound guidance, with 20 mL of 0.25% bupivacaine injected into the fascial plane between the rhomboid major and intercostal muscles, medial to the scapula. It is performed before general anesthesia under the same standardized dexmedetomidine sedation (0.5 mcg/kg load, then 0.3 mcg/kg/h).

Plazo: From arrival in the post-anesthesia care unit (PACU) to 24 hours postoperatively

Total rescue IV morphine (mg) given in the first 24 hours after surgery. Rescue morphine 2 mg IV is given when NRS at rest is ≥ 4 or on patient request, repeated every 10 minutes until NRS is \< 4.

Plazo: 1, 2, 4, 6, 12 and 24 hours after PACU arrival

Pain intensity on the Numerical Rating Scale (0 = no pain, 10 = worst imaginable pain), at rest and during ipsilateral shoulder abduction to 90°. If abduction isn't tolerated, three deep breaths are used instead.

Plazo: From PACU arrival to the first rescue morphine dose, assessed up to 24 hours postoperatively

Time (minutes) from PACU arrival to the first rescue morphine dose. Patients who need no rescue are censored at 24 hours.

Plazo: During surgery: from induction of anesthesia to end of surgery (approximately 2-3 hours)

Total fentanyl (mcg) given during surgery, including the induction dose and rescue doses (0.5 mcg/kg). Rescue is triggered when MAP or HR rises \> 20% above the pre-incision baseline for ≥ 2 minutes.

Plazo: 30 minutes after block injection

Number of dermatomes (T1-T6 and axilla) with reduced or absent cold sensation (ethyl chloride) on the operative side compared with the contralateral side. Block success is defined as ≥ 3 contiguous dermatomes.

Plazo: Assessed at 1, 2, 4, 6, 12, and 24 hours after PACU arrival (cumulative incidence up to 24 hours)

Number of patients with any episode of nausea, retching or vomiting.

Plazo: Assessed at 1, 2, 4, 6, 12, and 24 hours after PACU arrival (cumulative requirement up to 24 hours)

Number of patients needing rescue metoclopramide 10 mg IV.

Plazo: Periprocedural: during block performance, before induction of anesthesia

Time (seconds) from first placement of the ultrasound probe on the skin to needle withdrawal.

Plazo: Periprocedural: during block performance, before induction of anesthesia

Number of needle redirections needed to reach the target plane (maximum 3).

Plazo: From block performance up to 24 hours postoperatively

Number of patients with any of the following:

hypotension (MAP \< 65 mmHg or \> 20% decrease from baseline) bradycardia (HR \< 50 bpm) vascular puncture, hematoma or puncture-site infection pneumothorax (confirmed by lung ultrasound or chest X-ray) contralateral sensory block suggesting epidural spread local anesthetic systemic toxicity

Plazo: 1, 2, 4, 6, 12 and 24 hours after PACU arrival

Ramsay Sedation Scale (1 = anxious/agitated to 6 = no response).

Plazo: Baseline (preoperatively, on the day of surgery) and 24 hours postoperatively

Quality of Recovery-15 questionnaire score (range 0-150; higher scores mean better recovery).

Plazo: 24 hours postoperatively

5-point Likert scale (1 = very dissatisfied, 5 = very satisfied).

Plazo: 3 months postoperatively

Incidence of pain at or near the surgical site present on ≥ 4 of the 7 days before assessment, by structured telephone interview. Intensity is rated on the NRS (0-10), and neuropathic features are screened with the DN4 interview questionnaire (DN4i, score 0-7; ≥ 3 suggests neuropathic pain).

Ultrasound-Guided Retro Superior Costotransverse Ligament Space Block Versus Rhomboid Intercostal Block for Postoperative Analgesia After Modified Radical Mastectomy: A Randomized, Blinded Superiority Trial