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Hyponatremia in Dogs

Hyponatremia is the clinical term given to a condition in which a dog is suffering from low concentrations of serum sodium in the blood. As a component of the extracellular fluid (fluids outside of the cells), sodium is the most abundant positive charged atom in the body. For this reason, a condition of hyponatremia usually reflects a concurrent condition of hyposmolality, an underconcentration of osmotic solution in the blood serum; that is, a lack in the ability of body fluids to pass through the cellular membranes (osmosis), by which the body's chemical concentrations are kept in balance. Hyposmolality is typically associated with a decreased amount of sodium content throughout the body.

Theoretically, hyponatremia can be caused by either water retention or solute loss (loss of a dissolvable body substance -- in this case, salt/sodium is the solute). Most solute loss occurs in iso-osmotic solutions (e.g., vomit and diarrhea), and as a result, water retention in relation to solute is the underlying cause in almost all patients that are diagnosed with hyponatremia. In general, hyponatremia occurs only when there is a defect in the kidney's ability to excrete water.

Symptoms

• Lethargy
• Weakness
• Confusion
• Nausea/vomiting
• Seizures
• Dullness
• Coma
• Other findings depend on the underlying cause

Causes

Normal osmolar hyponatremia, causes with typical concurrent conditions:

• Hyperlipemia – excessive fats in the blood
• Hyperproteinemia
• Hyperosmolar hyponatremia

Hyperglycemia – excessive glucose/sugar in the blood

• Mannitol infusion (a diuretic agent)
• Normovolemic (normal blood volume)

Primary polydipsia – excessive thirst

• Hypothyroid myxedema (a skin and tissue disorder) coma
• Hypotonic fluid infusion (fluid with lower osmotic pressure)
• SIADH (syndrome of inappropriate antidiuretic hormone secretion)
• Hypervolemic (too much fluid in the blood)

Congestive heart failure (CHF)

• Hepatic (liver) cirrhosis
• Nephrotic syndrome (kidney disease where there is abnormal leakage of protein, low levels of proteins in blood and swelling of body parts)
• Hypovolemic (too little fluid in the blood)

Gastrointestinal losses

• Renal (kidney) failure
• Low potassium
• Cutaneous losses
• Diuresis (increased production of urine by the kidney)
• Hypoadrenocorticism (endocrine disorder)

Diagnosis

A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, a urinalysis and an electrolyte panel. If your dog has hyponatremia, these tests will confirm low serum sodium concentration. Other disorders that can mimic hyponatremia, and which will need to be excluded, are hyperglycemia, hyperproteinemia, and hyperlipidemia.

Your veterinarian may also recommend testing the serum osmolality will be tested. The osmolality balance of your dog's urine will be indicative of the kidney's ability to excrete water, and the sodium concentration found in the urine may indicate a low volume of circulating sodium.