What is hyponatremia?
Hyponatremia is a condition in which there is an excess of body water relative to body sodium1
Often defined as serum sodium concentration < 135 mEq/L
[Na+] < 135 mEq/L
Hyponatremia may be depletional, or dilutional2,3
- Depletional hyponatremia results from body electrolyte losses that are in excess of body water losses.3
- Dilutional hyponatremia results from retained water and is often associated with an excessive secretion of vasopressin.2,3
Hypotonic hyponatremia is classified into 3 main categories
These categories are based on the initial assessment of the patient's volume status, medical history, urine osmolality, and sodium concentration.1,3
The 3 main categories with their volume status are illustrated below.
|Hyponatremia Category||Total Body Water||Total Body Sodium||Extracellular Fluid||Edema|
Definition: A depletional form of hyponatremia that occurs when there is loss of sodium that exceeds water loss.1,3
SAMSCA is contraindaicated in hypovolemic and depletional hyponatremia, therefore this review focuses on euvolemic and hypervolemic hyponatremia.
Definition: A dilutional form of hyponatremia that occurs when the total serum sodium is normal or near normal, but the total body water is increased without clinically evident edema.1,3
Clinical Signs: No signs of volume depletion or volume expansion.1,3
Definition: A dilutional form of hyponatremia that occurs when there is an increase in total body water but a relatively smaller increase in the total serum sodium, so the available sodium is effectively diluted.1,3
Common Etiologies: Heart failure and renal disease (nephrotic syndrome and acute and chronic renal failure) are 2 primary causes of hypervolemic hyponatremia.1
Clinical signs: Signs of volume expansion, such as the presence of clinically evident edema, ascites, and pulmonary edema.3
The figure below provides a guide for classifying hyponatremia into categories.
Prevalence of Hyponatremia:
In the United States, the estimated prevalence of hyponatremia ranges from 3.16 million to 6.07 million persons.5
Certain medical conditions and medications have the potential to increase the risk of hyponatremia.2,6
|Selected Conditions3||Selected Drug Classes6|
Signs & Symptoms
Patients who experience hyponatremia may exhibit clinical manifestations that are largely related to central nervous system dysfunction. Signs and symptoms are important to recognize.2,7
|Signs and Symptoms of Hyponatremia7||Complications of Severe Hyponatremia2,7|
It has not been established that raising serum sodium with SAMSCA® (tolvaptan) provides a symptomatic benefit to patients