Analgesic Outcomes of Ultrasound-Guided QLB vs TAP Block in Midline Laparotomy

Midline laparotomy is associated with significant postoperative pain that can limit mobilization, impair respiratory function, and increase opioid-related side effects. Abdominal wall blocks such as the transversus abdominis plane (TAP) block and quadratus lumborum block (QLB) are used as part of multimodal analgesia. TAP primarily targets somatic afferents of the anterior abdominal wall, while QLB may provide broader coverage including potential paravertebral spread via the thoracolumbar fascia, potentially offering longer-lasting analgesia.

This single-center, prospective, randomized controlled trial will enroll 100 adults (50 per group) aged 18-65 years, ASA physical status I-III, scheduled for elective midline laparotomy under general anesthesia. Participants will be randomized 1:1 using sequentially numbered, opaque, sealed envelopes prepared by an independent research assistant. Both blocks will be performed after induction of general anesthesia and before surgical incision by an experienced anesthesiologist under ultrasound guidance and strict aseptic precautions.

Group A (QLB): Bilateral lateral quadratus lumborum (QL1) block with 20 mL of 0.25% bupivacaine per side (total 40 mL / 100 mg, not exceeding 2 mg/kg).

Group B (TAP): Bilateral TAP block with 20 mL of 0.25% bupivacaine per side (total 40 mL / 100 mg, not exceeding 2 mg/kg).

Postoperative analgesia will be standardized with intravenous paracetamol 1 g every 6 hours. Pain will be assessed using the Numerical Rating Scale (NRS 0-10) at 6, 12, and 24 hours by an independent, blinded outcome assessor. Rescue analgesia (intravenous morphine or tramadol) will be given for NRS ≥4. Primary and secondary analgesic outcomes include NRS scores, time to first rescue analgesia, proportion requiring rescue analgesia within 24 hours, and total opioid consumption in the first 24 hours. Block-related complications will also be recorded.

Statistical analysis will use SPSS version 26. Normality will be assessed by Shapiro-Wilk test. Continuous variables will be compared with independent-samples t-test or Mann-Whitney U test; categorical variables with Chi-square or Fisher's exact test. Potential confounders will be addressed by stratification. A two-sided p-value ≤0.05 will be considered statistically significant.

Inclusion criteria

• Age 18-65 years
• Either sex
• Scheduled for elective midline laparotomy (upper, lower, or full midline incision) under general anesthesia
• ASA physical status I-III

Exclusion criteria

• Body mass index >40 kg/m²
• Existing chronic pain disorder, established opioid dependence, or history of substance abuse
• Previous or current neurological or psychiatric illness likely to compromise comprehension, decision-making capacity, or reliable reporting of pain scores
• Conditions in which an abdominal wall block would not be appropriate or safe (bleeding tendency, ongoing anticoagulation outside acceptable limits, local skin or soft-tissue infection at the planned puncture site, or major distortion of abdominal wall anatomy)
• Urgent laparotomy performed for peritonitis or unstable physiology (including patients requiring continuous vasopressor support)
• Previous abdominal wall surgery, large incisional hernia, or distorted flank/anterior abdominal wall anatomy likely to impair standardized block placement