Background: Ultrasound-guided transversus abdominis plane block is an effective method of providing pain relief after cesarean delivery. Neuraxial morphine is currently the "gold standard" treatment for pain after cesarean delivery. In this study we tested the hypothesis that subarachnoid morphine would provide more prolonged and superior analgesia than would transversus abdominis plane block in patients undergoing elective cesarean delivery.

Methods: In this prospective, double-blind study, 57 patients were randomly assigned to receive either subarachnoid morphine (group SAM; n = 28) or transversus abdominis plane block (group TAP; n = 29). Patients received bupivacaine spinal anesthesia combined with morphine 0.2 mg in group SAM and received saline in group TAP. At the end of surgery, bilateral transversus abdominis plane block was performed using saline in group SAM or using bupivacaine 0.375% plus epinephrine 5 microg/mL in group TAP with 20 mL on each side. Postoperative analgesia for the first 24 hours consisted of scheduled rectal diclofenac and IV paracetamol; breakthrough pain was treated with IV tramadol. For the next 24 hours, scheduled rectal diclofenac was given; oral paracetamol and IV tramadol were administered upon patient request. Patients were assessed postoperatively in the postanesthesia care unit (time 0 hours) and at 2, 4, 6, 12, 24, 36, and 48 hours. The primary outcome measure was the time to first analgesic request.

Results: Median (range) time to first analgesic request was longer in group SAM than in group TAP [8 (2-36) hours versus 4 (0.5 to 29) hours (P = 0.005)]. Median (range) number of tramadol doses received between 0 and 12 hours was 0 (0-1) in group SAM versus 0 (0-2) in group TAP (P = 0.03). Postoperative visceral pain scores at rest and on movement during first the 4 hours were lower in group SAM than in group TAP, but were not different at any other time points. The incidence of moderate to severe nausea was higher in group SAM than in group TAP [13/28 (46%) versus 5/29 (17%) (P = 0.02)]. More patients developed pruritus requiring treatment in group SAM than in group TAP [(11/28 (39%) versus none (0%) (P < 0.001)].

Conclusion: As part of a multimodal analgesic regimen, subarachnoid morphine provided superior analgesia when compared with ultrasound-guided transversus abdominis plane block after cesarean delivery, yet at the cost of increased side effects.