In a patient with chronic hypernatremia, what complication must be considered when initiating rapid volume repletion and sodium reduction?

• A. Cerebral edema
• B. Hypoglycemia
• C. Osmotic demyelination syndrome
• D. Prolonged QT interval

Answer: (A)

In chronic hypernatremia, the brain adapts by accumulating osmolytes to prevent cell dehydration. If you begin rapid volume repletion and quickly lower the serum sodium, the extracellular environment becomes relatively hypotonic compared to the brain cells. Water then shifts into brain cells, leading to cerebral edema, increased intracranial pressure, and risk of herniation. That potential for brain swelling is the principal complication to guard against when correcting chronic hypernatremia, so correction should be slow and carefully controlled.

Osmotic demyelination syndrome is more classically linked to correcting chronic hyponatremia too rapidly, not hypernatremia. Hypoglycemia and prolonged QT are not the primary concerns in this situation.