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.
- Other findings depend on the underlying cause
Normal osmolar hyponatremia, causes with typical concurrent conditions:
Hyperlipemia – excessive fats in the blood
- 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)
- Renal (kidney) failure
- Low potassium
- Cutaneous losses
- Diuresis (increased production of urine by the kidney)
- Hypoadrenocorticism (endocrine disorder)
A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, a urinalysis and an electrolyte panel. If your cat 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 cat'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.
Primary treatment will depend on the severity of the hyponatremia, and the associated neurological symptoms. The severity of any underlying disorders will guide treatment priorities as well. Treatment generally consists of addressing the underlying cause, and increasing the serum sodium concentration if necessary.
Overly rapid normalization of the hyponatremia can have potentially severe neurological results, and may be more detrimental than the hyponatremia itself. Therefore, an isotonic saline is the fluid of choice in the large majority of cases. More aggressive correction of the serum sodium concentration with hypertonic saline is rarely necessary. Hypervolemic patients (patients with too much fluid in the blood) are typically managed with diuretics (fluid reducers) and salt restriction.
Conversely, hypovolemic patients (patients with too little fluid in the blood) are managed by replacing the volume deficit with isotonic saline. Other therapeutic interventions are dictated by the underlying cause of the hyponatremia.
Living and Management
Initially, your veterinarian will need to observe your cat's response to treatment, repeating serum sodium determinations in order to avoid overly rapid correction of the serum sodium concentrations, and to assure an appropriate response to sodium and other indicated therapies. In addition, your doctor will want to monitor your cat's hydration status and other serum electrolyte concentrations, as indicated by your cat's clinical condition and underlying disorder.