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 losses3
- Dilutional hyponatremia results from retained water and is often associated with an excessive secretion of vasopressin2,3
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.
|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 contraindicated 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.
Based on assessment of volume status, medical history, and urine osmolality and sodium concentrations, hyponatremia can be classified as hypovolemic, euvolemic, or hypervolemic. Douglas I. Hyponatremia: why it matters, how it presents, how we can manage it. Cleve Clin J Med. 2006;73(suppl 3):S4-S12. Reprinted with permission. Copyright © 2006 Cleveland Clinic. All rights reserved.
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
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