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 i.v. 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 i.v. Anesthesia was performed with propofol (2 mg/kg for induction, 6-8 mg.kg-1.h-1 for maintenance), fentanyl (3 micrograms/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 micrograms/kg). Postoperative analgesia was achieved with fentanyl (0.5 microgram/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 microgram.kg-1.min-1 versus magnesium group 0.058 +/- 0.01 microgram.kg-1.min-1; P < 0.05 and control group 0.021 +/- 0.013 microgram.kg-1.min-1 and magnesium group 0.0031 +/- 0.0018 microgram.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, i.v. magnesium sulfate administration reduces intraoperative and postoperative analgesic requirements compared with isotonic sodium chloride solution administration.
Implications: The perioperative administration of i.v. 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.