Hypernatremia definition: Sodium >145 mEq/L:
  • Mild hypernatremia: Serum sodium 146–155 mEq/L
  • Severe hypernatremia: Serum sodium >155 mEq/L


Divided into 3 categories

Hypovolemic Hypernatremia
  • Most common
  • Loss or deficiency of water and sodium with water losses being greater than sodium losses
  • Examples:
    • Renal failure
    • Medications (e.g., diuretics, lactulose)
    • Osmotic diuresis (mannitol, glucosuria, high-protein feedings)
    • Insensible losses (burns, sweating)
    • Respiratory loss
    • Defective thirst mechanism
    • Lack of access to water
    • Diarrhea/vomiting
    • Intubated patients

Isovolemic Hypernatremia
  • Water deficiency without sodium loss; free water loss
  • Examples:
    • Fever
    • Hypothalamic diabetes insipidus (DI):
      • Head trauma
      • Tumor
      • Congenital
      • Infection (TB, syphilis, mycoses, toxoplasmosis, encephalitis)
      • Granulomatous disease (sarcoid, Wegner)
      • Cerebrovascular accident
      • Aneurysm
    • Nephrogenic DI:
      • Congenital
      • Drugs (lithium, amphotericin B, foscarnet, demeclocycline)
      • Obstructive uropathy
      • Chronic tubulointerstitial disease (sickle cell nephropathy, multiple myeloma, amyloidosis, sarcoidosis, systemic lupus erythematosus, polycystic kidney)
      • Electrolyte disorders (hypercalcemia, potassium depletion)

Hypervolemic Hypernatremia
  • Gain of water and sodium, with sodium gain greater than water gain
  • Examples:
    • Iatrogenic – most common cause:
      • Sodium bicarbonate administration
      • NaCl tablets
      • Hypertonic parenteral hyperaliment
      • Hypertonic IV fluid (IVF)
      • Hypertonic dialysis
    • Hypertonic medicine preparations such as ticarcillin and carbenicillin
    • Cushing disease
    • Adrenal hyperplasia
    • Primary aldosteronism
    • Sea water drownings

Pediatric Considerations
  • More prone to iatrogenic causes
  • More likely to die or to have permanent neurologic sequelae
  • Morbidity ranges from 25–50% with mortality of 15%
  • May present with high-pitched cry, lethargy, irritability, muscle weakness
  • Poor breastfeeding and inappropriate formula preparations are a potential cause in neonates
  • Breastfed infants among the highest risk groups to develop hypernatremia
  • If hypernatremia is due to DKA, follow pediatric DKA protocols for fluid resuscitation
  • DDAVP dose for 3 mo–12 yr is 5–30 mcg/d intranasally
  • Consider NG hydration

Geriatric Considerations
  • Most commonly affected group due to impaired renal concentrating ability and reduced thirst mechanism
  • Consider neglect if underlying etiology is dehydration alone

Pregnancy Considerations
  • May encounter transient DI of pregnancy
  • Vasopressin and desmopressin are category B drugs in pregnancy
  • Hydration status much more difficult to evaluate accurately by exam

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