This study evaluates whether adding an ultrasound-guided rectus sheath block (RSB) to general anesthesia can improve pain control after midline laparotomy. Adult patients undergoing midline incision laparotomy will be randomly assigned to receive either general anesthesia alone or general anesthesia plus bilateral RSB with local anesthetic (bupivacaine 0.25%). After surgery, pain will be assessed using the Numeric Rating Scale (NRS) at 15 minutes, 1 hour, 3 hours, 6 hours, 12 hours, and 24 hours. The study will also compare the time to first opioid request, total opioid use during the first 24 hours after surgery, and changes in inflammation measured by the neutrophil-to-lymphocyte ratio (NLR). The goal is to determine whether RSB can reduce postoperative pain and opioid requirements and help limit postoperative inflammatory response.

This is a double-blind randomized controlled trial conducted in adult patients (18-64 years) undergoing midline incision laparotomy under general anesthesia at Sanglah Hospital. Eligible participants are enrolled consecutively and randomized using permuted block randomization with sealed envelopes into two parallel groups:

Group A (Control): General anesthesia without rectus sheath block.

Group B (Intervention): General anesthesia plus bilateral ultrasound-guided posterior rectus sheath block (RSB) using bupivacaine 0.25%.

Anesthetic management is standardized. Patients receive IV midazolam 0.02 mg/kg as premedication. Induction is performed with propofol 1-2 mg/kg and fentanyl 2 mcg/kg, followed by atracurium 0.5 mg/kg for intubation. Maintenance includes pressure-controlled ventilation (FiO₂ 40%, flow 2 L/min) and propofol infusion 50-150 mcg/kg/min. Intraoperative analgesia is supplemented with fentanyl 0.5 mcg/kg every 45 minutes. Hemodynamics are maintained within 20% of baseline.

RSB technique (Group B): After intubation, the abdominal skin is disinfected. A linear ultrasound probe is placed lateral to the umbilicus to identify the rectus abdominis muscle and posterior rectus sheath. Using an in-plane approach, a 50 mm needle is advanced from lateral to medial until the needle tip lies between the rectus abdominis muscle and posterior rectus sheath. After negative aspiration, 20 mL of bupivacaine 0.25% is injected as a single-shot on one side with aspiration every 3 mL, visualizing separation of the rectus muscle from the posterior sheath. The procedure is then repeated on the contralateral side (bilateral block).

Postoperative management and assessments: Pain is evaluated by an independent observer using the Numeric Rating Scale (NRS 0-10) at T1 (15 minutes in the recovery room), T2 (1 hour), T3 (3 hours), T4 (6 hours), T5 (12 hours), and T6 (24 hours) postoperatively. Postoperative analgesia includes patient-controlled analgesia (PCA) morphine demand-only (1 mg per demand dose) for patients with GCS 15, plus oral paracetamol 500 mg every 6 hours. The time to first opioid request is recorded (minutes), and total morphine consumption during the first 24 hours is collected.

Inflammation assessment: Neutrophil-to-lymphocyte ratio (NLR) is measured from complete blood count (CBC) preoperatively (one day before surgery) and postoperatively (in the recovery room).

Key outcomes include postoperative NRS scores (T1-T6), time to first opioid request, total opioid requirement in the first 24 hours, and perioperative changes in NLR.

Inclusion Criteria:

• Adults aged 18-64 years.
• Patients undergoing midline laparotomy incision (incision extending above to below the umbilicus) for digestive, obstetric, or oncology cases (corresponding to T7-T12 dermatomes) under general anesthesia.
• ASA physical status I-III.
• Body mass index (BMI) 18.5-30 kg/m².
• Willing and able to provide written informed consent.

Exclusion Criteria:

• Refusal to participate.
• Infection or wound at the planned block site.
• Decreased level of consciousness.
• Known allergy to local anesthetics or opioids.
• Coagulation disorder.
• History of chronic pain.
• Hyperalgesia.

De-identified individual participant data (IPD) will not be shared publicly. Data may be considered for sharing upon reasonable request to the principal investigator, subject to institutional and ethics approval

Participants were blinded to group assignment. Postoperative pain assessments (NRS) and outcome data collection were performed by an independent assessor who was blinded to allocation. Randomization codes were kept in sealed envelopes and were not disclosed to the assessor until data collection was completed. Data analysis was performed using coded group labels.