Comparison of Two Magnesium Sulfate Protocols in Opioid-Free Anesthesia for Bariatric Surgery

Background Opioid-free anesthesia has gained increasing interest in bariatric surgery to reduce opioid-related adverse effects. Intravenous magnesium sulfate is commonly used as part of multimodal analgesia in this setting; however, the optimal administration regimen remains unclear. Objective: to compare postoperative morphine requirements between two intravenous magnesium sulfate administration protocols within an opioid-free anesthesia framework in patients undergoing bariatric surgery. Methods This retrospective observational cohort study included adult patients with obesity (ASA II–III) who underwent laparoscopic bariatric surgery under standardized opioid-free total intravenous anesthesia at a single center between June 2022 and December 2023. Patients were allocated into two groups according to the magnesium sulfate regimen received: a single pre-induction bolus of 40 mg/kg (Mg Bolus group) or a pre-induction bolus of 50 mg/kg followed by a continuous intraoperative infusion of 15 mg/kg/h (Mg Bolus + Infusion group). The primary outcome was cumulative postoperative morphine consumption during the first 48 hours. Secondary outcomes included pain scores, postoperative nausea and vomiting, adverse events, and length of hospital stay. Results A total of 110 patients were included (55 per group). Postoperative morphine consumption during the first 48 hours was lower in patients receiving magnesium bolus plus infusion than bolus alone. Pain scores remained low in both groups. No clinically relevant differences were observed in adverse events or length of hospital stay. Conclusion In patients undergoing bariatric surgery under opioid-free anesthesia, a magnesium sulfate regimen consisting of a bolus followed by continuous infusion was associated with reduced postoperative morphine requirements compared with a single bolus strategy.