Analgesic efficacy of equal-dose bupivacaine diluted to 20 vs. 30 mL for anterior quadratus lumborum block after cesarean delivery: a randomized double-blind trial

BACKGROUND: The anterior quadratus lumborum (QL) block provides effective post-cesarean delivery analgesia, but the optimal local anesthetic (LA) volume remains unknown. This is critical for balancing efficacy and safety in pregnant patients. This study compared 20 mL versus 30 mL per side of equal-dose bupivacaine (120 mg) for anterior QL blocks. METHODS: Fifty patients undergoing elective cesarean section were randomized to receive bilateral anterior QL blocks with either 20 mL of 0.3% bupivacaine (QL20 group) or 30 mL of 0.2% bupivacaine (QL30 group). The primary outcome was the time to first postoperative morphine request. Secondary outcomes included extent of sensory blockade, pain scores, opioid consumption postoperative recovery, and technique-related side effects. RESULTS: The mean±SD time to first morphine request was 11.4±6.3 hours in the QL20 group and 15.7±6.3 hours in the QL30 group; the difference was not statistically significant (mean difference: 3.7 hours; 95% CI: -4.0, 12.6; P=0.288). However, the QL30 group reported significantly lower pain scores at rest and during movement between 4-8 hours postoperatively (P<0.05). Sensory blockade was more extensive in the QL30 group, covering T8-L1 compared to T9-L1 in the QL20 group. No cases of local anesthetic systemic toxicity were observed. CONCLUSIONS: Although increasing the volume for anterior QL block from 20 mL to 30 mL per side did not significantly extend analgesia duration, the higher volume improved pain scores and sensory spread. Both volumes remain viable options, and volume selection may be tailored to patient-specific considerations.