The use of intravenous magnesium sulfate on postoperative analgesia in orthopedic surgery A systematic review of randomized controlled trials

Introduction: The aim of this systematic review is to investigate the effects of perioperative intravenous administration of MgSO4 on postoperative pain, analgesic consumption and adverse effects in patients undergoing orthopedic surgery. Methods: Two investigators independently searched for articles on randomized controlled trials (RCTs) from 1998 to 2016 in Pubmed, Web of science and Google scholar. We evaluated clinical outcomes, comparing postoperative pain scores, cumulative analgesic consumption, time to first analgesia, and adverse effects between orthopedic surgery patients with and without the administration of MgSO4. Results: After screening 2350 articles, 11 RCTs (with a total sample size of 535 subjects) were included in this systematic review. Perioperative intravenous administered MgSO4 could reduce postoperative pain intensity compared with control in 6 trials (55%), but without significant difference in 5 trials (45%). With MgSO4 treatments, postoperative analgesic consumption was significantly reduced in 8 trials (73%), and without significant difference in 2 trials (18%). Two trials evaluated the time to first request of analgesic after surgery and showed prolong of 2.3 hours and 93 minutes respectively. MgSO4 group had less postoperative nausea (relative risk [RR]=0.32, 95% confidence interval [CI]=0.12-0.82, number needed to harm [NNH]=8.8), vomiting (RR=0.38, 95% CI= 0.15-0.92, NNH=9.7), and shivering (RR=0.31, 95% CI=0.11-0.88, NNH=5.2). Conclusion: Perioperative intravenous administration of MgSO4 in orthopedic surgery could reduce postoperative analgesic consumption and adverse effects such as vomiting, nausea, and shivering. These trials do not provide convincing evidence of beneficial effects on postoperative pain intensity and the time to first analgesic request. More trials should be conducted for the roles of MgSO4 in pain management for orthopedic surgery. However, intravenous MgSO4 administration should be considered as a strategy to relieve postoperative pain in orthopedic surgery patients.