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

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