Description

• Serum sodium (Na) concentration >145 mEq/L
• Often represents a state of hyperosmolality.
• Sodium concentration reflects balance between total body water and total body sodium. Hypernatremia occurs from deficit of water relative to sodium.
• Hypernatremia results from net water loss or, more rarely, from primary Na gain.
• May exist with hypo-, hyper-, or euvolemia, although hypovolemia is by far most common type:
  • Hypovolemic: Occurs with a decrease in total body water (TBW) and a proportionately smaller decrease in total body Na.
  • Euvolemic: No change in TBW with a proportionate increase in total body Na
  • Hypervolemic: Increase in TBW and a proportionately greater increase in total body Na

Epidemiology

• More common in elderly and young (1):
  • Occurs in 1% of hospitalized elderly patients (2)
• Gastroenteritis with diarrhea is the most common cause of hypernatremia in infants.
• Women are at an increased risk due to decreased TBW, as compared with men.

Risk Factors

• Infants/Children
• Old age
• Patients who are intubated/have altered mental status
• Diabetes mellitus
• Prior brain injury
• Surgery
• Diuretic therapy, especially loop diuretics
• Lithium treatment

Genetics
Some forms of diabetes insipidus may be hereditary.

General Prevention

• Treatment/Prevention of underlying cause
• Properly prepare infant formula and never add salt to any commercial infant formula.
• Keep patients well hydrated.

Etiology

• Pure water loss (total body Na normal) resulting from:
  • Adipsia/Hypodipsia (e.g., impaired thirst regulation, decreased access to water)
  • Nephrogenic diabetes insipidus (due to progressive renal dysfunction, hypercalcemia, hypokalemia, medication-related particularly lithium, or congenital)
  • Central diabetes insipidus (due to head trauma, stroke, meningitis)
  • Increased insensible water loss (e.g., fever, hyperventilation, hypermetabolic state, heat exposure, newborns under radiant warmers)
• Hypotonic fluid loss (total body Na decreased) resulting from:
  • Loss of fluid containing relatively more water than Na (e.g., excessive sweating, severe burns)
  • Urinary loss:
    • Osmotic diuresis: Hyperglycemia, mannitol
    • Diuretics, especially loop diuretics
    • Diabetes mellitus, particularly new presentation/decompensated
    • Post-ATN or postobstructive diuresis
    • Intrinsic renal disease
  • Gastrointestinal loss:
    • Diarrhea, especially in children
    • Vomiting, nasogastric (NG) lavage
    • Enterocutaneous fistula
• Excess Na (increase in total body Na) resulting from (2):
  • IV NaCl or NaHCO₃ during cardiopulmonary resuscitation, metabolic acidosis, or hyperkalemia
  • Sea water ingestion
  • Excessive use of NaHCO₃ antacid
  • Incorrect infant formula preparation
  • Intrauterine NaCl for abortion
  • Excessive Na in dialysate solutions
  • Disorders of the adrenal axis (Cushing syndrome, Conn syndrome, congenital adrenal hyperplasia)
  • Tube feeds

Commonly Associated Conditions

• Gastroenteritis
• Altered mental status
• Burns
• Hypermetabolic conditions
• Head injury
• Renal dysfunction