Hypernatremia Causes

Etiology of Hypernatremia

  • Impaired thirst response: elderly, NH patients, post-op, intubated, mental impairment, dementia. Inadequate intake of water is the most common cause.

    • Sensitivity of thirst declines with aging, hypernatremia often occurs in elderly patients in the setting of pneumonia, UTI (elderly NH Pt. with altered MS and UTI)

    • The dehydrated, shrunken brain "hangs" by the meninges in the skull which can tear the delicate bridging veins.

  • Secondary to water loss:

    • Extrarenal water loss: insensible losses as in diaphoresis, fever, tachypnea, mechanical ventilation, GI losses from osmotic diarrhea secondary to lactulose, sorbitol, or carbohydrate malabsorption, acute infectious diarrhea, enteral tube feedings.

    • Renal water loss: Osmotic diuresis as in glucosuria, high osmolar feeds, protein enteral tube feedings, ▲ urea as in high catabolic states, stress dose of steroids.

      • Non-osmotic urinary water loss: Central diabetes insipidus (inadequate ADH, Urine Osm <150 mOsm/L; after DDAVP - vasopressin administration, Urine Osm >300 mOsm/L)

        • Destruction of neurohypophysis from :

          • Head trauma

          • Sarcoidosis

          • Post-neurosurgical (craniopharyngioma, transphenoidal surgery)

          • Neoplastic (primary or metastatic)

          • Histiocytosis X

          • Meningitis/encephalitis

          • Idiopathic - many cases

      • Nephrogenic diabetes insipidus (inadequate renal response to ADH, Urine Osm <150 mOsm/L. No change in Urine Osm with DDAVP – vasopressin)

        • Electrolyte disorders (hypercalcemia, hypokalemia)

        • Drugs (lithium, demeclocycline, and amphotericin-B)

        • Medullary wash out (loop diuretics)

        • Recovery phase of ARF

        • Post urinary obstruction

        • Chronic renal disease

    • Iatrogenic causes may include from excess Na+ intake (hypertonic saline or NaHCO3)

      • 50 ml of NaHCO3 = 50 mEq NaHCO3 = 1000 mEq Na/L

    • Chronic mineralocorticoid excess.

    • Transcellular water shift from ECF to ICF can occur in circumstances of transient intracellular hyperosmolality, as in seizures or rhabdomyolysis.