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Hypermagnesemia

By

James L. Lewis III

, MD, Brookwood Baptist Health and Saint Vincent’s Ascension Health, Birmingham

Last full review/revision Sep 2021| Content last modified Oct 2021
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Hypermagnesemia is a serum magnesium concentration > 2.6 mg/dL (> 1.05 mmol/L). The major cause is renal failure. Symptoms include hypotension, respiratory depression, and cardiac arrest. Diagnosis is by measurement of serum magnesium concentration. Treatment includes IV administration of calcium gluconate and possibly furosemide; hemodialysis can be helpful in severe cases.

Even asymptomatic hypermagnesemia is rare in patients with normal renal function.

Symptoms and signs include hyporeflexia, hypotension, respiratory depression, and cardiac arrest.

Diagnosis of Hypermagnesemia

  • Serum magnesium concentrations > 2.6 mg/dL (> 1.05 mmol/L)

At serum magnesium concentrations of 6 to 12 mg/dL (2.5 to 5 mmol/L), the ECG shows prolongation of the PR interval, widening of the QRS complex, and increased T-wave amplitude.

Deep tendon reflexes disappear as the serum magnesium concentration approaches 12 mg/dL (5.0 mmol/L); hypotension, respiratory depression, and narcosis develop with increasing hypermagnesemia. Cardiac arrest may occur when blood magnesium concentration is > 15 mg/dL (6.0 to 7.5 mmol/L).

Treatment of Hypermagnesemia

  • Calcium gluconate

  • Diuresis or dialysis

Treatment of severe magnesium toxicity consists of circulatory and respiratory support and administration of 10% calcium gluconate 10 to 20 mL IV. Calcium gluconate may reverse many of the magnesium-induced changes, including respiratory depression.

Administration of IV furosemide can increase magnesium excretion when renal function is adequate; volume status should be maintained.

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