Magnesium sulphate as a technique of hypotensive anaesthesia

Background. This randomized, double-blind, placebo-controlled study was designed to assess the effect of perioperatively administered i.v. magnesium sulphate as a technique of hypotensive anaesthesia. Methods. Sixty patients (25 female) undergoing functional endoscopic sinus surgery were included in two parallel groups. The magnesium group received magnesium sulphate 40 mg kg(-1) i.v. as a bolus before induction of anaesthesia and 15 mg kg(-1) h(-1) by continuous i.v. infusion during the operation. The same volume of isotonic solution was administered to the control group. Intraoperative bleeding was evaluated using a quality scale. Results. In the magnesium group, there was a reduction in surgical time [68.1 (15.6) min vs 88.1 (10.7) min], although the anaesthetic time was 10 min longer and thus presuming a prolongation in anaesthetic emergence. There was a significant reduction of blood loss [165 (19) ml vs 257 (21) ml]. The anaesthetic requirements (fentanyl, vercuronium and sevoflurane), mean arterial blood pressure (P < 0.005) and heart rate (P < 0.005) were also significantly reduced. Conclusion. Magnesium sulphate led to a reduction in arterial pressure, heart rate, blood loss and duration of surgery. Furthermore, magnesium infusion alters anaesthetic dose requirements and emergence time.