Effects of calcium and magnesium pretreatment on hyperkalaemic cardiac arrest in rats

Background and objective: Administration of calcium safely and effectively reverses many of the electrophysiological actions of hyperkalaemia, but it has not been studied for pretreatment. Based on cellular studies, magnesium also has been suggested to prevent the effects of potassium on the heart. As their mechanisms of action differ, a combination of these drugs might have a synergistic protective action. Both compounds are inexpensive and can be administered safely in modest doses. We investigated whether magnesium, calcium or their combination could protect against hyperkalaemic cardiac arrest. Methods: Twenty-four adult rats were anaesthetized with halothane and randomly pretreated with CaCl2 15 mg kg(-1), MgSO4 30 mg kg(-1), CaCl2 7.5 mg kg(-1) + MgSO4 15 mg kg(-1) or physiological saline. Potassium (0.01 mmol kg(-1) h(-1)) was infused. The times to the first dysrhythmia, mean arterial pressure decrease to <40% of baseline and cardiovascular collapse were measured. Results: Serum potassium concentrations increased to similar values in all groups (to 12.0 +/- 0.2 mmol L-1 at the time of collapse). No differences in survival times were observed between groups. There was a trend for respiratory values to be better in the group receiving magnesium. Conclusions: Pretreatment with magnesium, calcium or a combination of both did not influence the time to cardiovascular collapse, and is therefore - at least in our model - not of any benefit in preventing hyperkalaemic cardiac arrest.