Are the Analgesic Effects of Morphine Added to Transversus Abdominis Plane Block Systemic or Regional? A Randomized Clinical Trial

Background: This study was designed to compare the effectiveness of the transversus abdominis plane (TAP) block with the addition of morphine to bupivacaine and the TAP block with bupivacaine plus intramuscular (IM) morphine. The aim of the study was to evaluate the effect of morphine administered with the TAP block on postoperative opioid consumption and pain scores and, secondarily, to determine whether the effect was systemic or local.Methods: This prospective, double-blind, randomized controlled trial included 52 patients. In the IM group, morphine at a dose of 0.1 mg/kg based on ideal body weight (IBW) was administered IM. In addition, a bilateral TAP block was performed under ultrasound guidance using a total of 40 mL of 0.25% bupivacaine, with 20 mL injected on each side. In the TAP group, an ultrasound-guided TAP block, including a total of 40 mL of 0.25% bupivacaine and 0.1 mg/kg morphine according to the IBW of patients, was administered bilaterally.Results: Total morphine consumption 24 h was 19.08 + 11.35 in the IM group and 11.81 + 7.02 in the TAP group, with an estimated difference in means of 7.2 (95% CI: 2.0, 12.5; p = 0.008). The morphine consumption after 6, 12, and 24 h was lower in the TAP group than in the IM group (p = 0.033, p = 0.003, and p = 0.008, respectively). The VAS scores at rest and during movement did not differ between the two groups. The total 24-h ondansetron consumption was higher in the IM group (p = 0.046). The postoperative heart rates, blood pressure, and peripheral oxygen saturation at 0, 1, 6, 12, and 24 h did not differ significantly between the groups.Conclusions: The addition of morphine to the TAP block may be an effective method for postoperative analgesia in gynecologic surgery and may not increase systemic side effects, due to the possible local effects of morphine administered interfacial.Trial Registration: ClinicalTrials.gov identifier: NCT05420337