Hyponatremia in Dogs
Hyponatremia is the medical term used to describe a condition in which a dog has low levels of sodium in its blood serum. Sodium is the predominant positively charged atom in the extracellular fluid, which refers to fluids outside of the cells. Therefore, when a dog experiences hyponatremia, it often indicates an accompanying condition of hyposmolality. Hyposmolality is characterized by an insufficient concentration of osmotic solution in the blood serum, resulting in an inability of body fluids to pass through cellular membranes, thus disrupting the body’s chemical balance. Hyposmolality typically correlates with a decreased sodium content throughout the body.
In theory, hyponatremia can stem from either water retention or solute loss. Solute loss, which involves the loss of a dissolvable substance in the body, such as salt or sodium, mainly occurs in iso-osmotic solutions like vomit and diarrhea. Consequently, water retention relative to solute loss is the primary cause of hyponatremia in most cases. Generally, hyponatremia only occurs when there is a defect in the kidney’s ability to excrete water.
Symptoms
- Lethargy
- Weakness
- Confusion
- Nausea/vomiting
- Seizures
- Dullness
- Coma
Other symptoms may vary depending on the underlying cause.
Causes
Normal osmolar hyponatremia, with associated conditions including:
- 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 leading to 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 characterized by abnormal protein leakage, low blood protein levels, and body swelling
- Hypovolemic (too little fluid in the blood)
- Gastrointestinal losses
- Renal (kidney) failure
- Low potassium
- Cutaneous losses
- Diuresis: Increased urine production by the kidney
- Hypoadrenocorticism: Endocrine disorder
Diagnosis
To diagnose sodium deficiency, a comprehensive blood profile will be conducted, including a chemical blood profile, complete blood count, urinalysis, and electrolyte panel. These tests will confirm if your dog has low serum sodium concentration, indicating hyponatremia. Additionally, other conditions that might mimic hyponatremia, such as hyperglycemia, hyperproteinemia, and hyperlipidemia, will need to be ruled out.
Your veterinarian may also recommend testing the serum osmolality to assess the balance of osmolality in your dog’s blood. Furthermore, analyzing the osmolality balance in your dog’s urine can provide insights into the kidney’s ability to excrete water, while the sodium concentration found in the urine may indicate a low volume of circulating sodium.
Treatment
The primary treatment approach will be determined by the severity of hyponatremia and the associated neurological symptoms, as well as the severity of any underlying disorders. Treatment primarily involves addressing the root cause of the condition and, if necessary, increasing the serum sodium concentration.
It’s essential to avoid overly rapid normalization of hyponatremia, as it can lead to potentially severe neurological consequences that may outweigh the effects of hyponatremia itself. Therefore, in the vast majority of cases, isotonic saline is the preferred fluid for correction. The use of hypertonic saline for aggressive correction of serum sodium concentration is seldom necessary.
Hypervolemic patients, those with excessive fluid in the blood, are usually managed with diuretics (fluid reducers) and salt restriction. Conversely, hypovolemic patients, those with insufficient fluid in the blood, are treated by replenishing the volume deficit with isotonic saline. Other therapeutic interventions are determined based on the underlying cause of hyponatremia.
Living and Management
Initially, your veterinarian will monitor your dog’s response to treatment by regularly assessing serum sodium levels. This is important to prevent overly rapid correction of serum sodium concentrations and to ensure an appropriate response to sodium and other necessary therapies. Additionally, your veterinarian will monitor your dog’s hydration status and other serum electrolyte concentrations based on your dog’s clinical condition and underlying disorder. Regular follow-up appointments may be necessary to track progress and adjust treatment as needed.
