Hyponatremia

Definition

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:

• Burns
• Congestive heart failure
• Diarrhea
• Use of medications called diuretics, which increase urine output
• Kidney diseases
• Liver cirrhosis
• Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
• Sweating
• Vomiting

Symptoms

Common symptoms include:

• Abnormal mental status
  • Confusion
  • Decreased consciousness
  • Hallucinations
  • Possible coma
• Convulsions
• Fatigue
• Headache
• Irritability
• Loss of appetite
• Muscle spasms or cramps
• Muscle weakness
• Nausea
• Restlessness
• Vomiting

Signs and tests

The health care provider will perform a complete physical examination to help determine the cause of your symptoms. Blood and urine tests will be done.

The following laboratory tests can confirm hyponatremia:

• Osmolality blood test
• Sodium blood test
• Urine osmolality
• Urine sodium

Treatment

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

Support Groups

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.

Complications

• Brain herniation
• Death
• 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.

Prevention

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.

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References

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.