Analgesic efficacy of continuous intravenous magnesium infusion as an adjuvant to morphine for postoperative analgesia: a systematic review and meta-analysis.

BACKGROUND The efficacy of perioperative intravenous magnesium administration on postoperative opioid use, opioid-related side effects (e.g., nausea and vomiting) and pain are uncertain, as randomized controlled trials on this topic have reported disparate results. The objective of this systematic review is to determine if perioperative magnesium reduces opioid use, opioid-related side effects, and postoperative pain. METHODS An electronic search was conducted using the Library of Medicine's PubMed and EMBASE databases. Included studies consisted of randomized controlled trials in an adult population with a clearly defined comparison of perioperative intravenous magnesium administration to a control with a documented assessment of opioid usage and postoperative pain. Relevant data was abstracted from included studies. Pooled estimates for weighted mean difference (WMD) with 95% confidence intervals (CI) were obtained for our primary outcome (opioid usage) using the Cochrane Collaboration's RevMan version 4.2.7 (Cochrane Collaboration; Oxford, United Kingdom). WMD and odds ratios (OR) were calculated using a random effects model. RESULTS The literature search ultimately yielded 22 trials, enrolling 1177 (599 magnesium, 578 control) patients, who were included in the analysis. A significant decrease in morphine usage by those patients who received magnesium was noted (WMD = -7.40; 95% CI: -9.40 to -5.41, p < 0.00001). Perioperative magnesium administration was not associated with a difference in postoperative nausea or vomiting (RR = 0.76; 95% CI: 0.52 to 1.09, p = 0.14). The pooled visual analog scores for pain at 4-6 hours after surgery were significantly less in those patients who received magnesium surgery (WMD = -0.67; 95% CI: -1.12 to -0.23, p = 0.003); however, there was no difference in pain scores at 20-24 hours after surgery (WMD = -0.25; 95% CI: -0.62 to 0.71, p = 0.17). CONCLUSION Based on the results of this systematic review, perioperative intravenous magnesium may be a useful adjuvant for the management of postoperative pain providing analgesia through a different mechanism of action than that of opioids and would make a potential addition to a multimodal anlgesic treatment plan; however, the decrease in opioid use with perioperative magnesium infusion does not appear to be associated with a decresea in opioid-related side effects.