Bilateral External Oblique Intercostal Plane Block Versus Intravenous Morphine for Rescue Pain Relief in Patients With Epidurals Following Upper Abdominal Surgeries: A Randomized Controlled Trial.

BACKGROUND

The management of postoperative pain after upper abdominal surgery is challenging. Thoracic epidural analgesia, though effective, has limitations, while intravenous (IV) morphine is associated with side effects. Ultrasound-guided external oblique intercostal block (EOIB) is an emerging regional technique for upper abdominal pain relief. We hypothesized that EOIB would provide superior pain relief to IV morphine in patients undergoing upper abdominal surgery. The main objective of the study was to compare pain relief from EOIB versus IV morphine as rescue analgesia in patients with moderate to severe pain despite an epidural after upper abdominal surgeries.

METHODS

This double-blinded, randomized controlled trial was conducted at a tertiary cancer hospital from January to November 2024. Patients aged ≥18 years undergoing upper abdominal surgery with pain on the numerical rating scale ≥4 despite epidural and IV paracetamol were randomized (1:1) to IV morphine (0.05 mg/kg, Arm A) or bilateral EOIB (0.1% bupivacaine 1 mL/kg and 4 mg dexamethasone, Arm B). The primary outcome was the total 24-hour morphine rescue requirement. Secondary outcomes included pain intensity difference (PID) at 0.5, 1, 4, 8, 12, 16, 20, and 24 hours, summated pain intensity difference at 8 and 24 hours (SPID), percentage PID in the first four hours, pain-free hours (PFH), and adverse events. Participants and outcome assessor nurses were blinded in the trial.

RESULTS

Of 101 screened patients, 66 were randomized with 33 in each group. The EOIB arm had significantly lower 24-hour morphine requirements compared to the morphine arm median (interquartile range) 0 mg (0-1.5) vs 2.5 mg (1-6.1), respectively; median difference (95% confidence interval [CI], 1.5 [0.00-3.40]; P = .006). Repeated measures analysis of variance with Greenhouse-Geisser correction determined that the mean PID did not differ among the two groups across different time points over 24 hours; F (7,434) = 1.08, P = .37. SPID at 8 and 24 hours favored EOIB (P = .038 and P = .048, respectively). The percentage PID in the first four hours was higher in the EOIB arm than morphine arm, 66.6% [58.5%-100%] vs 50% [34.9%-74%]; P = .002. PFH was significantly higher in the EOIB arm than morphine arm 4.00 [0.00-8.00] hours vs 0.00[0.00-0.37] hours; P = .015, with two patients achieving complete pain relief (NRS = 0) for 24 hours, compared to none in the IV morphine group. No significant adverse events were observed.

CONCLUSIONS

EOIB provided superior and prolonged analgesia compared to IV morphine as a supplement to epidural analgesia, reducing opioid consumption and increasing the pain-free period in patients undergoing upper abdominal surgery.