Magnesium sulfate reduces intra- and postoperative analgesic requirements

In a randomized, double-blind study with two parallel groups, we assessed the analgesic effect of perioperative magnesium sulfate administration in 46 ASA physical status I or II patients undergoing arthroscopic knee surgery with total IV anesthesia. The patients received either magnesium sulfate 50 mg/kg preoperatively and 8 mg.kg(-1).h(-1) intraoperatively or the same volume of isotonic sodium chloride solution IV. Anesthesia was performed with propofol (2 mg/kg for induction, 6-8 mg.kg(-1).h(-1) for maintenance), fentanyl (3 mu g/kg for induction), and vecuronium (0.1 mg/kg for intubation). Intraoperative pain was defined as an increase of mean arterial blood pressure and heart rate of more than 20% from baseline values after the induction of anesthesia and was treated with bolus fentanyl (1-2 mu g/kg). Postoperative analgesia was achieved with fentanyl (0.5 mu g/kg) and evaluated using the pain visual analog scale for 4 h. During the intraoperative and postoperative periods, patients in the magnesium group required significantly less fentanyl than those in the control group (control group 0.089 +/- 0.02 mu g.kg(-1).min(-1) versus magnesium group 0.058 +/- 0.01 mu g.kg(-1).min(-1); P < 0.05 and control group 0.021 +/- 0.013 mu g.kg(-1).min(-1) and magnesium group 0.0031 +/- 0.0018 mu g.kg(-1).min(-1): P < 0.01 for intraoperative and postoperative periods, respectively). We conclude that, in a clinical setting with almost identical levels of surgical stimulation, TV magnesium sulfate administration reduces intraoperative and postoperative analgesic requirements compared with isotonic sodium chloride solution administration. Implications: The perioperative administration of IV magnesium sulfate reduces intra- and postoperative analgesic requirements in patients with almost identical levels of surgical stimulus. Our results demonstrate that magnesium can be an adjuvant to perioperative analgesic management.