The effect of intravenous magnesium on postoperative morphine consumption in noncardiac surgery: A systematic review and meta-analysis with trial sequential analysis.

Systematic review and meta-analysis with trial sequential analysis of randomized trials in adults undergoing noncardiac surgery. The included studies compared prophylactic intravenous magnesium with placebo within a multimodal analgesia framework, across multiple surgical procedures and countries.

Prophylactic intravenous magnesium was administered perioperatively as a bolus, an infusion, or a bolus followed by infusion, with regimens varying widely across trials. Reported doses included bolus 50 mg/kg, bolus plus infusion 20 to 50 mg/kg or 250 mg, and infusion-only rates such as 2 to 65 mg/kg/h or 150 mg/h, given alongside multimodal analgesia and compared with placebo.

Adjunctive intravenous magnesium reduced postoperative morphine consumption in the first 24 hours, with a pooled mean difference of -5.6 mg (95% CI -7.54 to -3.66; P < 0.001; I2 = 92%) across 18 trials and 899 active-arm participants, and it delayed time to first analgesia by 143 minutes (95% CI 103 to 183; P < 0.001) in 11 trials with 824 active-arm participants. It did not meaningfully improve postoperative pain scores (MD -0.30 on a 0 to 10 scale, 95% CI -0.69 to 0.09; P = 0.13) or postoperative nausea and vomiting (OR 1.01, 95% CI 0.75 to 1.37; P = 0.93). Magnesium lowered shivering incidence (OR 0.26, 95% CI 0.15 to 0.44; P < 0.001) and increased postoperative serum magnesium concentration (MD 0.59, 95% CI 0.39 to 0.78; P < 0.001), while bradycardia was not significantly different (OR 1.13, 95% CI 0.43 to 2.98; P = 0.80). The authors concluded that intravenous magnesium may reduce opioid use after noncardiac surgery, with trial sequential analysis supporting a conclusive effect for morphine consumption.

The evidence was limited by substantial heterogeneity for several outcomes, including morphine consumption and serum magnesium concentration, and by risk of bias, indirectness, and imprecision. Dosing regimens and surgical settings varied widely across trials, which complicates interpretation and generalizability. Several outcomes showed no consistent benefit, and the evidence quality ranged from very low to moderate.