Background Peripheral abdominal nerve blocks contribute to multimodal postoperative analgesia that enhances early recovery after caesarean sections. The transversus abdominis plane (TAP) block is an established technique that offers somatic abdominal analgesia. The erector spinae plane (ESP) block is a novel fascial plane block that may offer additional visceral analgesic effects. This study aimed to compare the postoperative analgesic efficacy of bilateral ultrasound-guided ESP blocks to TAP blocks in women undergoing caesarean sections under spinal anaesthesia.

Methods Sixty-six ASA grade 1-3 (≥18 years) patients undergoing elective caesarean section under spinal anaesthesia were randomly allocated to receive either ESP blocks at the T9 vertebral level (n =33) or TAP blocks (n =33). The primary outcome measure was 24-hour cumulative morphine consumption. The secondary outcomes included the time taken to perform blocks, numeric rating scale (NRS) pain scores at 6- and 24-hours, effect of pain on activities of daily living (ADLs) and care for the newborn, time to first analgesic request, severity of opioid-related side effects, and patient satisfaction.

Results There was no statistically significant difference in mean (SD) 24-hour cumulative morphine consumption between the ESP blocks and TAP blocks: 27 mg (14) vs 32 mg (15) (p=0.185). ESP blocks took longer to perform: 10.7 minutes (2.2) vs 9.0 minutes (2.5) (p<0.01). There were no significant differences in the other secondary outcomes.

Conclusion ESP blocks did not significantly reduce postoperative analgesic requirements compared to TAP blocks after caesarean section under spinal anaesthesia. The ESP block did not demonstrate significant additional visceral analgesic effects.

Trial Registration South African National Clinical Trial Registry (DOH-27-102022-5278), Pan African Clinical Trials Registry (PACTR202301645957324)

Grant funding for stationery costs was supplied by the South African Society of Anaesthesiologists (SASA) Jan Pretorius Research Fund. The lead author (Aidan Eksteen) applied for funding from this fund and proof of stationery costs inured was re-imbursed to the lead author by the fund. A donation of block needles was supplied by Creatori Health (Pty) Ltd. and a donation of PCA infusion lines was supplied by Gabler Medical (Pty) Ltd. These companies are one of several approved medical equipment suppliers on tender to hospitals in South Africa. No authors receive financial remuneration from any of these companies.

Pan African Clinical Trials Registry: PACTR202301645957324 URL: https://pactr.samrc.ac.za/TrialDisplay.aspx?TrialID=24267 South African National Clinical Trials Register DOH-27-102022-5278 URL: https://sanctr.samrc.ac.za/TrialDisplay.aspx?TrialID=8100

Grant funding was supplied by the South African Society of Anaesthesiologists (SASA) Jan Pretorius Research Fund. Sponsorship of consumables was provided by Creatori Health (Pty) Ltd. and Gabler Medical (Pty) Ltd.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Human Research Ethics Committee of the University of the Witwatersrand, Johannesburg, South Africa gave ethical approval for this work on August 23, 2022 (Clearance number M220512)

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