Two Bupivacaine Concentrations for Rectus Intercostal Fascial Plane Block After Laparoscopic Cholecystectomy

Design. This is a prospective, randomized, double-blind (participant and outcomes assessor), controlled, single-centre trial to be conducted at Istanbul Medipol University Mega Hospital Complex after approval by the institutional ethics committee, in accordance with the Declaration of Helsinki, and registered prospectively on ClinicalTrials.gov. Written informed consent will be obtained from all participants.

Randomization and blinding. Before transfer to the operating room, patients will be allocated in a 1:1:1 ratio to one of three groups using a sequence generated with the Research Randomizer program. Study solutions for the two block groups will be prepared by an anesthesiologist not otherwise involved in the trial and supplied in identical, indistinguishable syringes labelled only with the randomization number (Group Y: 30 mL of 0.5% bupivacaine + 30 mL of 0.9% saline; Group D: 15 mL of 0.5% bupivacaine + 45 mL of 0.9% saline). As both solutions are clear, the anesthesiologist performing the block is also blinded to the concentration. All procedures are performed under general anesthesia, so participants are unaware of their allocation. All postoperative assessments will be performed by an anesthesiologist blinded to group allocation who takes no part in the intervention.

Groups. Group Y receives bilateral rectus intercostal fascial plane block (RIFPB) with 30 mL of 0.25% bupivacaine per side (60 mL, 150 mg in total). Group D receives bilateral RIFPB with 30 mL of 0.125% bupivacaine per side (60 mL, 75 mg in total). Group K (control) receives no block and is managed with the institution's routine analgesic protocol, including port-site infiltration with 30 mL of 0.25% bupivacaine performed by the surgical team. Total volume is held constant in both block groups; only the administered dose differs. To allow the isolated effect of the block to be assessed, port-site infiltration is not performed in the block groups. The total bupivacaine dose will not exceed 2.5 mg/kg in any group.

Anesthesia and surgery. After premedication with 2 mg of intravenous midazolam, general anesthesia will be induced with propofol (2-2.5 mg/kg), fentanyl (1-1.5 mcg/kg) and rocuronium (0.6 mg/kg), and maintained with sevoflurane and a remifentanil infusion (0.05-2 mcg/kg/min). Surgery will be performed by the same team using the conventional four-port technique. All patients will receive 4 mg of ondansetron for nausea prophylaxis, and 400 mg of ibuprofen and 100 mg of tramadol approximately 20 minutes before skin closure.

Block technique. The block will be performed bilaterally at the end of surgery, before extubation, with the patient supine and under general anesthesia. Using a high-frequency linear ultrasound probe (11-12 MHz) and an 80 mm block needle, the probe will be placed 3-4 cm lateral and caudal to the epigastrium to visualize the rectus abdominis muscle and the 6th and 7th costal cartilages. After hydrodissection with 5 mL of saline using an in-plane technique, 30 mL of the study solution will be injected on each side. Aspiration will be performed before injection, the drug will be given in fractionated doses, patients will be continuously monitored, and 20% lipid emulsion will be immediately available in the operating room.

Postoperative analgesia and assessment. All patients will receive 400 mg of intravenous ibuprofen three times daily. Pain will be assessed with the numeric rating scale (NRS, 0-10) at rest and on movement at 1, 3, 6, 12, 18 and 24 hours postoperatively. Rescue analgesia with 0.5-1 mg/kg of intravenous tramadol will be given whenever the NRS score is 4 or higher.

Withdrawal. Patients converted to open surgery after randomization will be excluded from the analysis.

Statistical analysis. Data will be analysed on an intention-to-treat basis. Normality of distribution will be assessed with the Shapiro-Wilk test. Normally distributed continuous variables will be compared among the three groups using one-way analysis of variance (ANOVA) with post hoc Bonferroni correction, and non-normally distributed variables using the Kruskal-Wallis test with post hoc Dunn correction. Categorical variables will be compared with the chi-square or Fisher exact test. Repeated NRS measurements will be analysed with repeated-measures ANOVA or the Friedman test as appropriate. A two-sided p value below 0.05 will be considered statistically significant.

Ethical considerations. Patients in the control group will not be deprived of analgesic treatment; they will receive the institution's routine port-site infiltration and standard multimodal analgesia protocol, and rescue analgesia whenever the NRS score is 4 or higher. Both bupivacaine doses compared are within the safe range, and the total dose is halved in the low-concentration group. Patient data will be stored in coded form. The study has no financial support and the investigators declare no conflict of interest.