Analgesic and Respiratory Effects of Two Doses of Morphine as an Adjunct to Bupivacaine in Ultrasound-Guided Transversus Abdominis Plane Block in Upper Abdominal Surgery

Background: Opioid receptors are present at the terminals of afferent peripheral nerves; therefore, administration of opioids peripherally might provide a significant analgesic effect. Objectives: We investigated the analgesic efficacy of 2 different doses of morphine in bilateral subcostal single-injection ultrasound-guided transversus abdominis plane (TAP) block in abdominal surgery. Study Design: Randomized, controlled, double-blind trial. Setting: University hospital. Methods: We enrolled 90 patients (aged 18-60 years) who were scheduled for elective upper abdominal surgeries and received TAP block for postoperative analgesia. Patients received 20 mL bupivacaine 0.5% (group B) only or combined with 10 mg morphine (group BM10) or 15 mg morphine (group BM15). Study drugs were diluted with saline solution 0.9% to 40 mL volume and bupivacaine concentration of 0.25% and injected 20 mL on each side. Primary outcome was the verbal rating pain scale (VRS) over the first 24 hours postoperatively. Secondary outcomes were time to first request for analgesics, total analgesic consumption, lung spirometry, and adverse effects. Results: Compared with group B, patients in BM10 and BM15 groups showed significantly lower postoperative VRS scores at rest and during cough. Patients in BM15 group had lower VRS scores at the 24th hour postoperatively at rest (P = 0.034) and during cough (P = 0.040), compared with group BM10, with no significant difference at other timepoints. The median time to first request for intravenous patient controlled analgesia (PCA) nalbuphine was 10 hours (range, 6-12 hours) in group B versus 15 hours (8-18 hours; P= 0.000) and 16 hours (10-23 hours; P= 0.000) in BM10 and BM15 groups, respectively. Total consumption of nalbuphine PCA in BM15 group was 12 mg (6-18 mg) compared with 26 mg (20-34 mg; P= 0.000) and 18 mg (12-24 mg; P= 0.000] in groups B and BM10, respectively, with a significant difference between BM10 and BM15 groups (P = 0.000) and without significant adverse effects. Limitations: A limitation was a small sample size. Conclusions: Addition of morphine to bupivacaine in single-injection subcostal TAP block controlled pain and reduced opioid requirements after abdominal surgery in a dose-dependent manner.