Hyponatremia in Cats

As a component of the extracellular fluid (fluids outside of the cells), sodium is the most abundant positive charged atom in the body. The term hyponatremia refers to a condition in which a cat is suffering from abnormally low concentration of serum sodium in the blood. Hyponatremia usually reflects a concurrent condition of hyposmolality; that is, an underconcentration of osmotic solution in the blood serum -- 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)