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.