Background During the postoperative period of elective cesarean section, intrathecal morphine is effective in the multimodal analgesic regimen, but can cause significant adverse effects. Bilateral posterior quadratus lumborum block could be alternatively used. The aim of this study was to compare efficacy and safety of both strategies as part of a multimodal analgesic regimen.

Methods This was a prospective, randomized, blinded, controlled study. 104 parturients were randomly selected to receive intrathecal morphine or posterior quadratus lumborum block during cesarean section under spinal anesthesia. The primary endpoint was patient-controlled 24-hour cumulative intravenous morphine use. Secondary endpoints were 48-hour cumulative morphine use, static/dynamic pain scores, functional recovery (ObsQoR-11 questionnaire) and adverse effects.

Results There was no statistical difference in the mean cumulative morphine dose at 24-hour between groups (posterior quadratus lumborum block group, 13.7 (97.5% CI 10.4 to 16.9) mg; intrathecal morphine group, 11.1 (97.5% CI 8.4 to 13.8) mg, p=0.111). Pain scores did not show any difference between groups, excepted at 6 hours for the pain at cough/movement in favor of the posterior quadratus lumborum block group (p=0.013). A better recovery quality was observed at 24 hours in the posterior quadratus lumborum block group (p=0.009). Pruritus was more frequent in intrathecal morphine group parturients (35% vs 2%)

Conclusions No difference in cumulative morphine dose at 24 hours was observed in posterior quadratus lumborum block group compared with intrathecal morphine group. Posterior quadratus lumborum block can be considered an alternative to intrathecal morphine in cesarean postoperative analgesia, especially in cases of intolerance to morphine.

Trial registration number NCT04755712.