Effects of magnesium sulphate on suxamethonium-induced complications during rapid-sequence induction of anaesthesia

Twenty patients were studied in a double-blind manner to investigate whether magnesium sulphate, when given during a rapid-sequence induction of anaesthesia, lessens the side effects caused by suxamethonium. Patients were randomly allocated to two groups; equal volumes of either magnesium sulphate (40 mg.kg^-1) or saline were given during rapid-sequence induction of anaesthesia, after thiopentone but before the administration of suxamethonium (1.5 mg.kg^-1). The changes in the serum potassium concentration, the degree of muscle fasciculations and the presence of postoperative myalgia were recorded. The mean serum potassium concentration increased by 0.08 mmol.l^-1 in the magnesium group and by 0.1 mmol.l^-1 in the control group at 2 min after injection of suxamethonium; in neither group was there a significant increase from baseline values. The systolic blood pressure and heart rate increased in both groups after tracheal intubation. The incidence of fasciculations was significantly lower in the magnesium group. Magnesium did not clinically prolong muscle relaxation. There was no difference between the groups in the incidence of myalgia after surgery (one patient in each group). Since no significant increase in the serum potassium concentration was demonstrated, no assessment could be made of the effect of magnesium sulphate on the serum potassium concentration after administration of suxamethonium.