MAGNESIUM-SULFATE REDUCES INTRA-OPERATIVE AND POSTOPERATIVE ANALGESICREQUIREMENTS

In a randomized, double-blind study with two parallel groups, we asses sed the analgesic effect of perioperative magnesium sulfate administra tion in 46 ASA physical status I or II patients undergoing arthroscopi c knee surgery with total IV anesthesia. The patients received either magnesium sulfate 50 mg/kg preoperatively and 8 mg.kg(-1).h(-1) intrao peratively 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), an d vecuronium (0.1 mg/kg for intubation). Intraoperative pain was defin ed as an increase of mean arterial blood pressure and heart rate of mo re than 20% from baseline values after the induction of anesthesia and was treated with bolus fentanyl (1-2 mu g/kg). Postoperative analgesi a was achieved with fentanyl (0.5 mu g/kg) and evaluated using the pai n visual analog scale for 4 h. During the intraoperative and postopera tive periods, patients in the magnesium group required significantly l ess 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).m in(-1) and magnesium group 0.0031 +/- 0.0018 mu g.kg(-1).min(-1): P < 0.01 for intraoperative and postoperative periods, respectively). We c onclude that, in a clinical setting with almost identical levels of su rgical stimulation, TV magnesium sulfate administration reduces intrao perative and postoperative analgesic requirements compared with isoton ic sodium chloride solution administration. Implications: The perioper ative administration of IV magnesium sulfate reduces intra- and postop erative analgesic requirements in patients with almost identical level s of surgical stimulus. Our results demonstrate that magnesium can be an adjuvant to perioperative analgesic management.