Evaluation of effects of magnesium sulphate in reducing intraoperative anaesthetic requirements.

Background: The present randomized, placebo-controlled, double-blind study was designed to assess the effect of peroperatively administered i.v. magnesium sulphate on anaesthetic and analgesic requirements during total i.v. anaesthesia.

Methods: Eighty-one patients (36 women, 45 men) undergoing elective spinal surgery were included in one of two parallel groups. The magnesium group received magnesium sulphate 30 mg kg(-1) as a bolus before induction of anaesthesia and 10 mg kg(-1) h(-1) by continuous i.v. infusion during the operation period. The same volume of isotonic solution was administered to the control group. Anaesthesia was maintained with propofol (administered according to the bispectral index) and remifentanil (adjusted according to heart rate and arterial blood pressure) infusions.

Results: A significant reduction in hourly propofol consumption was observed with magnesium administration. For example, the mean infusion rate of propofol in the second hour of the operation was 7.09 mg kg(-1) h(-1) in the control group vs 4.35 mg kg(-1) h(-1) in the magnesium group (P<0.001). The magnesium group required significantly less remifentanil (P<0.001) and vecuronium (P<0.001). No side-effects were observed with magnesium administration.

Conclusion: The administration of magnesium led to a significant reduction in the requirements for anaesthetic drugs during total i.v. anaesthesia with propofol, remifentanil and vecuronium.