Effects of different dose regimens of magnesium on pharmacodynamics and anesthetic requirements of balanced general anesthesia

The present double- blind, randomized, placebo- controlled study was designed to assess the effect of two different dose regimens of magnesium sulphate [MgSO[4] administration on intraoperative propofol and vecuronium requirements and postoperative fentanyl consumption in patients undergoing hernioraphy. Sixty patients were allocated to three equal groups; two magnesium groups and control group. Magnesium groups received 50 mg kg[-1] of magnesium preoperatively followed by intravenous infusion of magnesium 8 mg kg[-1] h[-1] [Mgl G] or 16 mg kg[-1]h[-1] [Mg2 G]. Patients in control group received the same volume of isotonic solution. Anesthesia was induced and maintained with propofol, fentanyl, and vecuronium. Magnesium Gs required significantly lower propofol [121.0 +/- 4.5, 117.4 +/- 6.3 micro g kg[-1] min.[-1] in Mgl and Mg2 Gs respectively vs. 153.8 +/- 8.4 micro g kg[-1] min.[-1] in control G], and vecuronium requirements [0.097 +/- 0.008, 0.092 +/- 0.006 mg kg[-1] h[-1] in Mgl and Mg2 Gs respectively vs. 0.124 +/- 0.01 mg kg[-1] h in control G]. Magnesium significantly shortened the onset time of vecuronium [154.0 +/- 25.9, 162.0 +/- 22.4 sec. in Mgl and Mg2 Gs respectively vs. 227.4 +/- 10.9 sec. in control], prolonged its clinical duration [44.7 +/- 3.2, 46.4 +/- 5.1 min. in Mgl and Mg2 Gs respectively vs. 26.0 +/- 3.9 min. in control] and prolonged its recovery index which was significantly longest in Mg2 G [25.4 +/- 1.9 min.] compared to Mgl G [20.1 +/- 2.1 min.] and control [15.3 +/- 1.4 min.] Fentanyl consumption on the first postoperative day was significantly higher in control [1.52 +/- 0.08 micro g kg[-1] than in magnesium Gs [0.96 +/- 0.07, 0.91 +/- 0.08 micro g kg[-1] in Mgl and Mg2 Gs respectively]. Postoperative sedation score showed significantly the highest value in Mg2 G compared to Mgl and control Gs. Mean arterial blood pressure and heart rate were lower in magnesium groups with lowest value in Mg2 G. It is concluded that magnesium 50 mg kg[-1] bolus followed by 8 mg kg[-1] h[-1] leads to significant reductions in intraoperative propofol and vecuronium and postoperative fentanyl consumption. Doubling magnesium infusion rate added minimal benefits on the expense of haemodynamic consequences and delayed recovery