Comparison of Postoperative Morphine Requirements Between Two Magnesium Sulfate Administration Protocols in Opioid-Free Anesthesia for Bariatric Surgery
Comparison of Postoperative Morphine Requirements Between Two Magnesium Sulfate Administration Protocols in Opioid-Free Anesthesia for Bariatric Surgery
This retrospective observational study aims to compare postoperative morphine consumption in patients undergoing bariatric surgery with opioid-free anesthesia (OFA) using two different intravenous magnesium sulfate administration protocols: a single bolus versus a bolus followed by continuous infusion. Medical records of 110 patients operated between June 2022 and December 2023 at Hospital HM Nou Delfos were reviewed. All patients received standardized OFA, and only the magnesium protocol varied between the groups. The primary objective was to evaluate total morphine consumption during the first 48 hours postoperatively. Secondary outcomes included pain scores, antiemetic use, and adverse events. This study was approved by the hospital's Research Ethics Committee (Protocol V3_12.05.2025).
This is a retrospective, single-center, observational study conducted at Hospital HM Nou Delfos (Barcelona, Spain), which compares the effect of two intravenous magnesium sulfate (MgSO₄) administration protocols on postoperative opioid requirements in patients undergoing bariatric surgery under opioid-free anesthesia (OFA).
The two magnesium protocols evaluated were:
Group A: MgSO₄ bolus 40 mg/kg administered before induction.
Group B: MgSO₄ bolus 50 mg/kg before induction followed by continuous infusion of 15 mg/kg/h until the end of surgery.
All patients underwent standardized OFA including propofol, lidocaine, ketamine and dexmedetomidine. No intraoperative opioids were administered. Multimodal postoperative analgesia was provided in all cases(dexamethasone, paracetamol, and dexketoprofen).
A total of 110 patients were included in the analysis, as defined in the original approved protocol (55 per group).
The primary outcome was cumulative morphine consumption in the first 48 hours postoperatively.
Secondary outcomes included:
Pain scores at rest and with movement at 2, 6, 12, 24, and 48 hours
Use of rescue analgesics
Incidence of postoperative nausea and vomiting (PONV)
Adverse events potentially related to OFA (e.g., hypotension, bradycardia)
Data were extracted from electronic health records and analyzed using descriptive and inferential statistical methods. This study aims to contribute real-world evidence on magnesium strategies in OFA and to support the development of safe, cost-effective analgesic protocols in bariatric patients.
Inclusion Criteria:
Age between 18 and 65 years
Body mass index (BMI) ≥ 30 kg/m²
ASA physical status II or III
Underwent laparoscopic bariatric surgery (sleeve gastrectomy or Roux-en-Y gastric bypass) under opioid-free total intravenous anesthesia
Exclusion Criteria:
Pregnancy or breastfeeding
Chronic opioid use before surgery
Known allergy to magnesium sulfate or any drug used in the anesthetic protocol
Severe renal or hepatic insufficiency
Untreated coagulopathy
Active substance abuse
Uncontrolled psychiatric disorders
Intraoperative complications requiring deviation from the protocol
Postoperative morphine consumption exceeding institutional standards