Hypernatremia

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What this article covers

• Overview

  Definition: hypernatremia is a serum sodium concentration above 145 mEq/L (145 mmol/L), less common than hyponatremia but associated with increased mortality in hospitalized and critically ill patients.

• Epidemiology

  Elderly patients and infants are disproportionately affected: the elderly from blunted thirst, reduced total body water, and immobility; infants because they depend entirely on caregivers for free water.

• Risk factors

  Impaired thirst or altered mental status: patients unable to sense or act on thirst (elderly, sedated, intubated, dementia) cannot compensate for ongoing water losses.

• Pathophysiology

  Hypotonic fluid loss with inadequate replacement (most common mechanism): diarrhea, excessive sweating, respiratory losses, or osmotic diuresis (glucosuria) remove water in excess of sodium; nonrenal…

• Clinical features

  Neurologic findings from brain cell shrinkage are the hallmark, ranging from lethargy, irritability, and confusion to seizures and coma; severity correlates with the rate and magnitude of the sodium rise more than the absolute level.

• Differential diagnosis

  Central diabetes insipidus: urine osmolality rises after desmopressin, confirming ADH deficiency rather than resistance.

• Diagnosis

  Hypernatremia is confirmed by a serum sodium above 145 mEq/L (145 mmol/L), and, because it is always associated with hyperosmolality, no serum osmolality measurement is needed to confirm the disorder…

• Management

  First, determine the pathogenesis (hypotonic loss, hypertonic gain, or ADH defect), because management differs by mechanism.

• Complications

  Cerebral edema and herniation from overly rapid correction: correcting chronic hypernatremia faster than about 0.5 mEq/L/hr (over 10-12 mEq/L/day) allows water to shift into the still-hyperosmolar…

• Prognosis

  Outcome depends heavily on the rate of correction: appropriately paced correction (no faster than 0.5 mEq/L/hr when chronic) prevents cerebral edema and generally allows full neurologic recovery.

• Prevention

  Proactively offer oral fluids to at-risk patients (elderly, sedated, intubated, or cognitively impaired) rather than relying on thirst to prompt intake, since impaired thirst is the leading contributor to hospital-acquired hypernatremia.