External Oblique Intercostal Plane Block and Subcostal Transversus Abdominis Plane Block in Minimally Invasive Hepatectomy: Non-inferiority Trial

[Anesthesia and Induction] Except for the specific nerve block technique assigned to each group, all participants will receive the standard anesthetic care for minimally invasive hepatectomy at Seoul National University Hospital. No premedication will be administered before entering the operating room, where standard non-invasive monitoring will be established. Anesthesia will be induced with remifentanil target-controlled infusion, propofol, and rocuronium after loss of consciousness. Endotracheal intubation will be performed after neuromuscular blockade. Anesthesia will be maintained with desflurane and remifentanil infusion, adjusted according to clinical requirements. As a part of the perioperative care, palonosetron (0.075 mg) and dexamethasone (5 mg) will be given intravenously during induction for antiemetic prophylaxis, and intravenous acetaminophen (1 g) and nefopam (20 mg) will be administered before the start of surgery. [Interventional Procedures] Following the induction of anesthesia, all nerve blocks will be performed under ultrasound guidance using a high-frequency convex probe covered with a sterile sheath under aseptic conditions. For the External Oblique Intercostal (EOI) block group, the T10 rib will be located at the intersection of the midclavicular line and the umbilical line, and the clinician will count upwards to identify the T6, T7, and T8 ribs. The probe will then be placed perpendicular to the rib trajectory at the T6-7 or T7-8 intercostal space to identify the external intercostal plane. Using an in-plane approach with an 8-cm needle, the plane will be confirmed via hydrodissection with 1-2 mL of saline, followed by the bilateral injection of 20 mL of 0.375% ropivacaine per side (total 40 mL). In contrast, for the Subcostal Transversus Abdominis Plane (TAP) block group, the probe will be placed on the subxiphoid midline and moved laterally along the T12 rib to identify the transversus abdominis plane. The needle will be advanced to the plane between the internal oblique and transversus abdominis muscles, and similarly, 20 mL of 0.375% ropivacaine will be injected into each side (total 40 mL) after confirming the plane with saline. [Postoperative Analgesia and Outcomes] Postoperative pain will be managed primarily using a fentanyl-based patient-controlled analgesia (PCA) device (Accumate 1200, Woo Young Medical), set with a loading dose of 50 mcg, a demand-only bolus of 20 mcg, and a 10-minute lockout time without basal infusion. A scheduled non-opioid regimen, consisting of intravenous acetaminophen (1 g) and nefopam (20 mg) every 8 hours, will be maintained for 48 hours, transitioning to oral acetaminophen (650 mg) once oral intake resumes. In the Post-Anesthesia Care Unit (PACU), if a patient reports a Numerical Rating Scale (NRS) score of 7 or higher despite active PCA use (exceeding four times per hour), a rescue dose of 50 mcg of intravenous fentanyl will be provided.