The Analgesic Efficacy of Subarachnoid Morphine in Comparison With Ultrasound-Guided Transversus Abdominis Plane Block After Cesarean Delivery: A Randomized Controlled Trial

Abstract

The gold standard treatment for pain after cesarean delivery is subarachnoid morphine (SAM). Use of morphine, however, is associated with a number of adverse effects and with medical contraindications and logistic issues that limit its use. An effective alternative is ultrasound-guided transversus abdominis plane (TAP) block. This treatment method provides real-time imaging of the needle trajectory and injectate spread, and may improve both safety and nerve block effectiveness. SAM not only has a longer duration of effective pain relief as compared with TAP block, but also relieves abdominal wall-derived pain, and unlike TAP block, relieves visceral pain from the uterus. This prospective, randomized, double-blind study tested the hypothesis that SAM provides more prolonged and superior analgesia as compared with a TAP plane block in patients undergoing elective cesarean delivery. Patients were randomly assigned to receive treatment with SAM (n = 28) or TAP block (n = 29). Spinal anesthesia was initiated in SAM patients with bupivacaine combined with 0.2 mg morphine; TAP block patients received saline. At the end of surgery, bilateral TAP block was performed in SAM patients using 20 mL of saline or in TAP block patients using bupivacaine plus epinephrine with saline on each side. For the first 24 hours, postoperative analgesia was provided by rectal diclofenac and intravenous (IV) paracetamol; breakthrough pain was managed with IV tramadol. In the second 24 hours, patients received rectal diclofenac; oral paracetamol and IV tramadol were given upon patient request. Postoperatively, patients were evaluated in the postanesthesia care unit at 0 hours and at 2, 4, 6, 12, 24, 36, and 48 hours. The time to first analgesic request was longer in the SAM group compared with the TAP group (median [range] for SAM was 8 [2-36] hours vs. 4 [0.5 to 29] for TAP block; P = 0.005). Patents in the SAM group received a lower median number of tramadol doses between 0 and 12 hours (median [range] for SAM was 0 [0―1] vs. 0 [0-2] for the TAP block group; P = 0.03). In the first the 4 hours after surgery, visceral pain scores at rest and on movement were lower in the SAM group compared with the TAP group, but were not different at all other time points. Moderate to severe nausea occurred more frequently in the SAM group than in the TAP group (13/28 [46%] vs. 5/29 [17%], respectively; P = 0.02) and the frequency of pruritus requiring treatment was higher (SAM: 11/28 (39%) vs. TAP: none (0%) (P< 0.001). The investigators conclude from these findings that SAM as part of multimodal analgesia after cesarean delivery achieves superior pain relief than TAP block but is also associated with more adverse effects.