Magnesium Imbalance

Magnesium supports neuromuscular stability, cardiac conduction, and the function of several cellular enzymes. Its concentration is controlled primarily by renal excretion. When glomerular filtration falls, magnesium clearance falls with it, so routine replacement can accumulate and cause hypermagnesemia. Dialysis-related losses and renal wasting can have the opposite effect, producing hypomagnesemia. Hypomagnesemia is a serum magnesium below 0.7 mmol/L (approximately 0.70 mmol/L); severe deficiency is below 0.5 mmol/L. The number matters, but the patient’s presentation determines urgency. A patient with a modestly low result and no symptoms may need oral replacement, whereas a patient with a very low result, seizure, or ventricular dysrhythmia needs an emergency response. Low magnesium removes some of the normal restraint on neuromuscular and cardiac excitability. The patient may develop tremor, muscle cramps, weakness, neuromuscular irritability, confusion, seizures, QT prolongation, or ventricular arrhythmias. Potassium may remain low despite potassium replacement; this refractory hypokalemia should prompt the nurse to consider magnesium deficiency. Excess magnesium depresses neuromuscular and cardiovascular function. Worsening hypotension, reduced respiratory effort, and loss of deep tendon reflexes are toxicity findings, not evidence that replacement is...