Medical Encyclopedia


Medical Encyclopedia

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Contents of this page:

Alternative Names   

Dilutional hyponatremia; Euvolemic hyponatremia; Hypervolemic hyponatremia; Hypovolemic hyponatremia

Definition    Return to top

Hyponatremia is a metabolic condition in which there is not enough sodium in the body fluids outside the cells.

Causes    Return to top

Sodium circulates in the 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 sodium levels drop in the fluids outside the cells, water will seep into the cells to balance the salt levels. The cells will swell as a result of the excess water. Although most cells can handle this swelling, brain cells cannot, because the skull confines 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:

Hyponatremia is the most common electrolyte disorder in the United States.

Causes of hyponatremia include:

Symptoms    Return to top

Common symptoms include:

Exams and Tests    Return to top

The following laboratory tests can confirm hyponatremia:

A complete physical examination will also be done to find the cause of this condition. During this examination, your doctor may order other tests.

Treatment    Return to top

The cause of hyponatremia must be treated, especially in the case of cancer where radiation, chemotherapy, or surgery to remove the tumor may correct the sodium imbalance. Other treatments depend on the type of hyponatremia.

Treatments to correct hyponatremia may include:

Outlook (Prognosis)    Return to top

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.

Possible Complications    Return to top

When to Contact a Medical Professional    Return to top

Hyponatremia can be a life-threatening emergency. Call your health care provider if you have symptoms of this condition.

Prevention    Return to top

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.

References    Return to top

Braunwald E, Fauci AS, Kasper DL, et al., eds. Hyponatremia. In Harrison's Principles of Internal Medicine. 15th ed. New York, NY: McGraw-Hill; 2001:274-76.

Update Date: 8/14/2007

Updated by: Charles Silberberg, DO, Private Practice specializing in Nephrology; Affiliated with NY Medical College, Division of Nephrology, Valhalla, NY. Review provided by VeriMed Healthcare Network.

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