Administration of Magnesium Sulphate Prior to Vecuronium: Effects on the Speed of Onset and Duration of Neuromuscular Block

Background: We commonly encounter surgical patients who are on magnesium therapy in the operation theatre. It is important to know the interaction of magnesium on anaesthetic drugs including neuromuscular blocking agents. Our aim is to observe and compare the onset and duration of action of vecuronium following magnesium pre-treatment. Material and Method: 50 patients were randomly divided into 2 groups. Group 1 (n = 25) received placebo (normal saline) and group 2 (n=25) received 40 mg/kg magnesium sulphate added to 100 ml of normal saline infused over a period of 15 minutes prior to induction. Following the induction of anaesthesia muscle relaxation was achieved by 0.1 mg/kg vecuronium and time for onset, duration of neuromuscularblock and vecuronium dose requirement during surgery was assessed by monitoring the tactile response to Train of four stimulation. Results: Onset of time for intubation was significantly reduced to 120.19±6.53 seconds in the magnesium group compared to 259.150±26.131 seconds in thecontrol group(P< 0.001). It was observed that the average duration of neuromuscular blockage of vecuronium was almost doubled and statistically significant (P = 0.001) in the magnesium group(26.89±2.91) as compared to the control group (42.28±1.41).The total dose of vecuronium used or required was significantly less in the magnesium group when compared to the control group (p=0.008). Duration from last dose of vecuronium to reversal of anaesthesia was prolonged in the magnesium group (40.2±3.96) compared to the control group(29.8±6.03) which is statistically significant(p<0.001). Conclusion: Magnesium sulphate administered before vecuronium significantly accelerates the onset of neuromuscular block necessary for intubation of trachea and significantly increase the time course of neuromuscular blockade. Intraoperative consumption of vecuronium was less in the magnesium group.