Equis ISSN 2398-2977


Contributor(s): Sarah Binns, Graham Munroe


  • Serum sodium concentration >144 mEq/l (144 mmol/l). 
  • 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 osmolarity. 
  • 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, therefore knowledge of the hydration of an animal is important for accurate interpretation of serum sodium concentrations. 
  • Hypernatremia usually implies hyperosmolarity, ie an absolute or relative water deficiency.
  • Cause: excessive sodium intake/retention; inadequate water intake; excessive water loss.
  • Signs: dehydration, weakness, depression, coma, seizures.
  • Diagnosis: history, clinical signs, biochemistry, hematology, urinalysis.
  • Treatment: fluid replacement.
  • Prognosis: fair, depending on cause and severity.



  • Excessive sodium intake or retention, especially iatrogenic.
  • Inadequate water intake.
  • Excessive water loss.
  • Water loss exceeding sodium loss.

Predisposing factors

  • Free water loss.
  • Increased sodium intake.


  • 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)   Sodium chloride  . 
      • Administration of sodium bicarbonate   Sodium bicarbonate  . 
      • Administration of total parenteral nutrition   Nutrition: parenteral  . 
      • 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 (DI)   Diabetes insipidus  : 
      • Central (inadequate release of ADH). 
      • Nephrogenic (inadequate response to ADH).
    • Fever (high insensible water loss). 
    • High environmental temperature or prolonged exercise leading to high insensible water loss (often associated with panting/hyperventilation).
    • Prolonged hyperventilation, eg pulmonary disease, acidosis   Acid-base imbalance  , anemia   Anemia: overview  .
    • Exhausted horse syndrome.
  • 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.


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Schaer M (1999) Disorders of serum potassium, sodium, magnesium and chloride. JVEEC (4), 209-217 VetMedResource.
  • Leon L A S (1998) Treatment of exercise-induced dehydration. Vet Clin North Am - Equine Pract 14 (1), 159 PubMed.
  • Heath S E, Peter A T, Janovitz E B et al (1995) Ependymoma of the neurohypophysis and hypernatremia in a horse. JAVMA 207 (6), 738-741 PubMed.
  • Johnson P J (1995) Electrolyte and acid-base disturbances in the horse. Vet Clin North Am Equine Pract 11, 491-514 PubMed.
  • Lloyd D R and Rose R J (1995) Effects of sodium bicarbonate on fluid, electrolyte and acid-base balance in racehorses. Brit Vet J 151 (5), 523-545 PubMed.

Other sources of information

  • Corley K T T (2004) Correction of Acid-base and Electrolyte Disturbances. In: Equine Clinical Pharmacology. Eds: Bertone J J & Horspool L J I. Saunders, USA. pp 352-353.
  • Wingfield W E & Raffee M R (2002) Eds. The Veterinary ICU Book. Teton New Media, Jackson Hole, USA. 
  • Schmall L M (1997) Fluid and Electrolyte Therapy. In: Current Therapy in Equine Medicine 4. Ed: Robinson N E. W B Saunders, USA.