Magnesium

Magnesium is the second most abundant cation in intracellular fluid.  It is an important part of many enzyme systems, especially working in the metabolism of carbohydrates and proteins.  It is important for the health of the immune system, DNA synthesis, neurotransmission, and for maintaining a regular heart rhythm.

The normal range of magnesium is 1.5-2.5 mEq/L.

Hypomagnesemia (magnesium levels lower than 1.5 mEq/L) is rarely seen in people who have a well-balanced diet, but this imbalance is being identified more often due to increased knowledge about the electrolyte.  Signs and symptoms of this imbalance are tremors, tetany, seizures, cardiac abnormalities (such as premature ventricular contractions, atrial or ventricular fibrillation, ventricular tachycardia, and ECG changes), neuromuscular irritability, depression, confusion, and difficulty swallowing.  This is caused by chronic alcoholism, GI losses, abuse of diuretics or laxatives, malabsorption syndromes (such as Crohn’s disease), and malnourishment.  To treat this imbalance, replace magnesium by an oral supplement or IV magnesium sulfate.  Increased dietary intake also helps restore this balance.  It is important to monitor cardiac rhythm and deep tendon reflexes of a patient being treated for hypomagnesemia.  You should monitor for digitalis toxicity; signs of this are nausea, anorexia, and sudden changes in heart rate or rhythm.  It is also important to provide safety measures if the patient is experiencing confusion.

Hypomagnesemia is a common cause of hypokalemia and hypocalcemia that are unresponsive to treatment.  It is important to correct the magnesium imbalance before correcting these other imbalances.

Increased levels of magnesium (>2.5 mEq/L) is known as hypermagnesemia.  This is a rare disorder.  It is caused by renal failure, excessive IV magnesium replacements, administration of magnesium-containing antacids or laxatives, and administration of potassium-sparing diuretics.  Signs and symptoms include muscle weakness, fatigue, CNS depression, decreased cardiac impulse transmission (resulting in decreased heart rate and low blood pressure), absent deep tendon reflexes, shallow respirations, and facial flushing.  Respiratory paralysis may occur.  To treat hypermagnesemia, all oral and IV magnesium should be discontinued.  When treating this imbalance, be sure monitor cardiac rhythm and deep tendon reflexes, just as you would with hypomagnesemia.  Be prepared to support ventilation if respiratory paralysis occurs and have IV calcium prepared to antagonize potential cardiac and respiratory complications.  Because calcium and magnesium have the same charge, calcium will come into the blood stream and push magnesium into the cell.  If the patient has renal failure, hemodialysis may be necessary.

Question of the day:

What medication must a nurse have on hand when treating patients with hypermagnesemia?

 

References

McCarthy, M. (2011). Electrolyte imbalances [PowerPoint Slides].

White, B. (2009). Clients with electrolyte imbalances. In Black, J. M., & Hawks, J. H. (Eds). Medical-surgical nursing. Clinical management for positive outcomes, (Vol 1., 8th Ed), (pp. 151-167). St. Louis, MO: Elsevier Inc.

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