BASICS
- A serum sodium concentration less than the lower limit of normal horses is generally<132 mEq/L.
- Sodium is the major extracellular cation in the body, and therefore, is critical for maintenance of the extracellular space
- Serum sodium concentration reflects the ratio of the whole-body sodium to whole-body water; therefore, knowledge of the hydration state is important for accurate interpretation of serum sodium concentrations
- Hyponatremia usually results from relative water excess and is usually not clinically significant until serum sodium concentrations are <122 mEq/L
- Systems affected
- Nervous—cerebral edema (also seen with rapid correction of severe hyponatremia)
- Renal/urologic—medullary washout
- Hemic/lymphatic/immune—intravascular hemolysis
- Lethargy
- Tremors
- Abnormal gait
- Central blindness
- Seizures
- Severity of signs depends on the rapidity and degree of hyponatremia
- Loss of sodium-containing fluid—diarrhea, pronounced sweating, hemorrhage, excessive gastrointestinal fluid drainage by nasogastric intubation, excessive pleural fluid drainage, saliva loss, sustained exercise, protein-losing enteropathies, colitis, and acute kidney injury (usually in foals)
- Adrenal insufficiency (e.g. iatrogenic) or adrenal exhaustion
- Sequestration of fluid (third spacing)—peritonitis, ascites, uroperitoneum (usually in foals), and gut torsion, volvulus, obstruction, or ileus
- Iatrogenic—administration of hypotonic fluids or diuretics
- Inappropriate water retention—psychogenic polydipsia, renal disease, inappropriate antidiuretic hormone secretion, heart failure, hepatic fibrosis, and severe hypoalbuminemia
- Prolonged diuresis secondary to hyperglycemia and glucosuria may result in medullary washout and subsequent hyponatremia and hypochloremia
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS