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.