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Hyponatremia is a metabolic condition in which there is not enough sodium (salt) in the body fluids outside the cells.
- Alternative Names
Dilutional hyponatremia; Euvolemic hyponatremia; Hypervolemic hyponatremia; Hypovolemic hyponatremia
- Causes, incidence, and risk factors
Sodium is found mostly in body fluids outside the cells. It is very important for maintaining blood pressure. Sodium is also needed for nerves and muscles to work properly.
When the amount of sodium in fluids outside cells drops, water moves into the cells to balance the levels. This causes the cells to swell with too much water. Although most cells can handle this swelling, brain cells cannot, because the skull bones confine them. Brain swelling causes most of the symptoms of hyponatremia.
In hyponatremia, the imbalance of water to salt is caused by one of three conditions:
- Euvolemic hyponatremia -- total body water increases, but the sodium content remains the same
- Hypervolemic hyponatremia -- both sodium and water content in the body increase, but water gain is greater
- Hypovolemic hyponatremia -- water and sodium are both lost from the body, but the sodium loss is greater
Hyponatremia is the most common electrolyte disorder in the United States.
Causes of hyponatremia include:
- Signs and tests
The cause of hyponatremia must be diagnosed and treated. In some cases, cancer may cause the condition, and radiation, chemotherapy, or surgery to remove the tumor may correct the sodium imbalance.
Other treatments depend on the specific type of hyponatremia.
Treatments may include:
- Fluids through a vein (IV)
- Medication to relieve symptoms
- Water restriction
- Expectations (prognosis)
The outcome depends on the condition that is causing the problem. In general, acute hyponatremia, which occurs in less than 48 hours, is more dangerous. When sodium levels fall slowly over a period of days or weeks (chronic hyponatremia), the brain cells have time to adjust and swelling is minimal.
- Brain herniation
- Possible coma
- Calling your health care provider
Hyponatremia can be a life-threatening emergency. Call your health care provider if you have symptoms of this condition.
Treating the condition that is causing hyponatremia can help. If you play any demanding sports, drink fluids that contain electrolytes (“sports drinks”). Drinking only water while you take part in high-energy athletic events can lead to acute hyponatremia.
Skorecki K, Ausiello D. Disorders of sodium and water homeostasis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 117.
Review Date: 11/6/2009
Reviewed By: A.D.A.M. Editorial Team: David Zieve, MD, MHA, Greg Juhn, MTPW, David R. Eltz. Previously reviewed by David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine (8/3/2009).