ISSN 2398-2969      




  • Definition: serum sodium concentration >158 mEq/L.

    Normal ranges and abnormal values are dependent on equipment used and reference ranges established for that equipment.
  • Sodium is the major cation of extracellular fluid (ECF).
  • It does not freely move into the intracellular space (ICF) of most cells but is dependent on the action of the Na/K ATPase pump and it is therefore the major determinant of plasma osmolality.
  • Water moves freely between the ECF and ICF following an osmotic gradient.
  • Measured serum sodium concentration does not reflect total body sodium content but indicates the amount of sodium relative to the amount of ECF water.
  • Hypernatremia always implies hyperosmolality.



  • Free water loss.
  • Increased sodium intake.

Predisposing factors

  • None.


  • Serum sodium concentration is a reflection of the amount of sodium relative to the volume of total body water.
  • Hypernatremic patients may have decreased, increased or normal total body sodium content.
  • Hypernatremia must be assesed with volume status.
  • Hypernatremia associated with hypervolemia (impermeant solute gain):
    • Salt poisoning.
    • Iatrogenic:
      • Administration of hypertonic saline (3% or 7.5% NaCl).
      • Administration of sodium bicarbonate Sodium bicarbonate.
      • Administration of total parenteral nutrition.
      • Hyperaldosteronism.
      • Hypercortisolism (rarely severe hypernatremia).
  • Hypernatremia associated with normovolemia or mild hypovolemia (pure water loss).
    • Primary hypodipsia or adipsia.
    • Associated with:
    • Inadequate access to water.
    • Diabetes insipidus Diabetes insipidus :
      • Central (inadequate release of ADH).
      • Nephrogenic (inadequate response to ADH).
    • Fever (high insensible water loss).
    • High environmental temperature leading to high insensible water loss (often associated with panting).
  • Hypernatremia associated with hypovolemia (hypotonic fluid loss):
  • Third space losses:
  • Burns.
  • Renal losses:


  • Clinical signs more common with severe, acute hypernatremia.
  • If hypernatremia chronic (over at least 2-3 days) it is possible that there will be no or minor clinical signs.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • De Morais H A & DiBartola S P (2008) Hypernatremia: a quick reference. Vet Clin Small Animal Practice 38 (3), 485-489 PubMed.
  • Schaer M (1999) Disorders of serum potassium, sodium, magnesium and chloride. JVEEC (4), 209-217 VetMedResource.

Other sources of information

  • Small Animal Critical Care Medicine. (2008) Eds D C Silverstein and K Hopper. Saunders Elsevier, St Louis, Missouri.
  • Fluid, Electrolytes and Acid-base Disorders in Small Animal Practice. (2006) Eds S P DiBartola, Saunders Elsevier, St Louis Missouri.
  • The Veterinary ICU Book (2002) Eds W E Wingfield and M R Raffee. Teton New Media, Jackson Hole, WY.

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