Systemic magnesium reduces postoperative morphine consumption

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Background: Several studies suggested that systemic magnesium reduces postoperative opioid consumption and intensity of pain, but some reported conflicted findings. The efficacy and safety profile of intravenous magnesium in non-cardiac surgery remain uncertain. Objectives: The primary aim of this review was to investigate the effect of intravenous magnesium on the consumption of postoperative morphine in the first 24 hours in adults undergoing non-cardiac surgery. Design: Systematic review and meta-analysis with trial sequential analysis Data sources: MEDLINE, EMBASE, CENTRAL from their inception until January 2019 Eligibility criteria: All randomised clinical trials comparing intravenous magnesium versus placebo in non-cardiac surgery were systematically searched in the databases. Observational studies, case reports, case series and non-systematic reviews were excluded. Results: Fifty-one trials (n=3,311) were included for quantitative meta-analysis. In comparison to the placebo, postoperative morphine consumption at 24-hour was significantly reduced in the magnesium group, with a mean difference (95% CI) of -5.60 mg (-7.54 to -3.66), ρ<0.001, I2= 92%; level of evidence: low. The trial sequential analysis for the effect of magnesium on postoperative morphine consumption was conclusive. Patients who received magnesium was associated with a longer time to request first analgesia (95% CI 143 minutes (103 to 183), ρ<0.001, I2= 99%; level of evidence: low) and lower incidence of shivering (95% CI 0.26 (0.15 to 0.44), ρ<0.001, I2= 35%; level of evidence: very low). However, no significance differences were demonstrated in postoperative pain score in the first 24 hours (mean difference 95%CI -0.30 (-0.69 to 0.09), ρ=0.13, I2= 91%; level of evidence: low), bradycardia (odd ratio 95%CI 1.13 (0.43 to 2.98), ρ=0.80, I2= 35%; level of evidence: very low) and postoperative nausea and vomiting (odd ratio 95%CI 0.90 (0.67-1.22), ρ=0.49, I2= 25%; level of evidence: moderate). Conclusions: Low-quality of randomised evidence with substantial heterogeneity demonstrates that the adjunctive use of intravenous magnesium as part of the multimodal analgesia may reduce the mean morphine consumption in the first 24 hours and delay the time to request for first analgesia in patients undergoing non-cardiac surgery. Trial Registration: CRD42018086846

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