1. Study Rationale and Background Postoperative pain and PONV are prevalent after laparoscopic cholecystectomy, leading to patient discomfort, prolonged hospitalization, and increased resource use. The PROSPECT guidelines recommend a multimodal approach, including intraperitoneal saline lavage, to mitigate pain by diluting irritants and reducing acidosis. However, even with this approach, PONV rates remain high (30-50%).
Ondansetron, a 5-HT3 antagonist, is a established antiemetic. Emerging evidence indicates a peripheral analgesic mechanism via blocking 5-HT3 receptors on nociceptive neurons, inhibiting neuropeptide release, and potential local anesthetic effects. Administering it intraperitoneally targets the site of surgical trauma. A previous study (Abdelaziz et al., 2021) using 4mg showed promise, but it had a small sample size and was not integrated into a strict, modern multimodal protocol. This pilot study addresses this gap by testing an 8mg dose within a rigorous, standardized PROSPECT-aligned protocol, using the AUC-VAS/24h to comprehensively capture the pain burden.
2. Overall Study Design and Methodology This is a single-center, prospective, phase IV, randomized, controlled, triple-blind, parallel-group pilot study, designed and reported according to CONSORT guidelines for pilot trials.
Blinding (Triple):
Patients are unaware of their assignment.
Care Providers \& Outcome Assessors: Surgeons, anesthesiologists, nurses, and research interns collecting data are all blinded.
Data Analyst: The statistician performs the initial analysis on coded data (Group A/B) before unblinding.
Randomization: A computer-generated sequence using permuted blocks (sizes 4 and 6), stratified by sex and ASA status (I vs. II), will allocate patients 1:1. Allocation is concealed using sequentially numbered, opaque, sealed envelopes. A designated "blinding coordination nurse" opens the envelope, prepares the identical-looking study solution, and labels it only with a code (A or B).
3. Standardization of Procedures A strict, standardized perioperative protocol is mandated for all participants to minimize variability.
Preoperative:
Dexamethasone 8mg IV (antiemetic), antibiotic prophylaxis.
Intraoperative:
Anesthesia: Standardized induction (Midazolam 0.02-0.03 mg/kg, Fentanyl 2-4 mcg/kg, Propofol 1-2 mg/kg, Cisatracurium 0.15 mg/kg) and maintenance (Sevoflurano 1-1.5 MAC). Multimodal analgesia: Acetaminophen 1g IV and Diclofenac 75mg IV.
Surgery: Pneumoperitoneum pressure strictly maintained at 10-12 mmHg. Four-port technique with identical placement. Pre-incisional infiltration of all port sites with Bupivacaine 0.75% (up to 20 ml total). Critical view of safety dissection. Active and complete aspiration of pneumoperitoneum at closure.
Intervention: The assigned solution (500ml) is instilled into the peritoneal cavity for 5 minutes with the patient in a 20° Trendelenburg position, followed by complete aspiration.
Postoperative:
Scheduled analgesics: Acetaminophen 1g (every 8 hours) and Diclofenac 75mg IV (every 12 hours).
Rescue Analgesia: Buprenorphine 75mcg SC is administered only upon patient request AND a pain score ≥50mm on the VAS or ≥6 on the Faces Pain Scale-Revised (FPS-R).
Rescue Antiemesis: Metoclopramida 10mg IV is permitted for PONV. The use of intravenous ondansetron is prohibited during the entire perioperative period to avoid confounding the intervention's effects.
4. Objectives and Endpoints as a Pilot Study As a pilot trial, its primary goal is to assess feasibility, refine procedures, and obtain preliminary estimates of effect and variability to power a future definitive trial. The primary outcome, AUC-VAS/24h, integrates pain intensity and duration, providing a robust measure of the "total pain burden." All secondary outcomes (PONV, rescue analgesia consumption, sleep quality) are explicitly exploratory and hypothesis-generating.
5. Safety and Monitoring The safety of intraperitoneal saline lavage and ondansetron is well-established. The combination presents minimal anticipated risk. All adverse events and postoperative complications will be actively monitored and recorded for the first 24 hours and up to 30 days post-surgery. An interim analysis for safety and efficacy will be conducted after 50% recruitment (n=20). Any serious adverse events will be reported promptly to the Institutional Ethics Committee.
6. Significance This is the first study to evaluate the combination of standard saline lavage with 8mg of intraperitoneal ondansetron within a rigorously standardized, PROSPECT-aligned, multimodal protocol. Using a triple-blind pilot design and a comprehensive primary endpoint, it will generate high-quality preliminary evidence on this simple, low-cost intervention's efficacy and safety in a Mexican population. The results will determine the feasibility and inform the design of a larger, definitive multicenter randomized controlled trial.
