Effects of Systemic Magnesium on Postoperative Analgesia: Is the Current Evidence Strong Enough?

Background: Clinical studies have been previously carried out on the efficacy of systemic magnesium to minimize postoperative pain, however, with controversial results. A quantitative meta-analysis was performed to evaluate the analgesic efficacy and safety of systemic magnesium on post-operative pain. Study Design: Comprehensive systematic review of all relevant, publsished randomized controlled trials. Methods: A search was conducted of published literature in MEDLINE, PsycINFO, Scopus, EMBASE, and the Cochrane Central Register of Controlled Trials (CENTRAL) databases from inception to September 2014. Randomized controlled trials (RCTs) that compared magnesium with placebo were identified. Effects were summarized using standardized mean differences (SMDs), weighed mean differences (WMD), or odds ratio (OR) with suitable effect model. Results: Twenty-seven RCTs involving 1,504 patients were included. In total, peri-operative magnesium significantly reduced the pain score at rest (SMD, -1.43, 95% CI, -2.74 to -0.12, < 0.01). Magnesium significantly reduced analgesic consumption (SMD, -1.72, 95% CI, -3.21 to -0.23) in patients undergoing urogenital, orthopaedic, and cardiovascular surgeries, but was inconclusive for patients receiving gastrointestinal surgeries. The obvious analgesia of systemic magnesium was observed on reducing the pain score during movement at 24 hours after operation (SMD, -0.05, 95% CI, -0.43 to 0.32). Moreover, magnesium administration showed a beneficial effect with regard to intra-operative hemodynamics and reduced extubation time in the cardiovascular surgery patients (WMD, -29.34 min, 95% CI, -35.74 to -22.94, P < 0.01). Limitations: Focused only on the quality of analgesia on postoperative pain with regards to surgery type. Conclusions: Our study suggests that systemic magnesium during general anesthesia significantly decreases post-operative pain scores without increasing adverse events. It should be noted that since there are 18 ongoing RCTs without published data, it is still premature to draw conclusions on the long-term analgesic effects of magnesium as well as potential gender or age difference. Key words: Magnesium, post-operative pain, meta-analysis