Overhydration

Overhydration is having too much water in the body.

When more fluid is consumed than can be excreted, overhydration occurs. The blood vessels overfill, and fluid moves from the blood vessels into the spaces around cells, causing swelling (edema).

Overhydration has many causes. The most common is heart failure, which occurs when the heart cannot pump blood adequately. Kidney disorders can cause overhydration if the kidneys cannot excrete enough water. Overhydration can also occur when the body produces too much antidiuretic hormone (which signals the kidneys to retain more water). Overproduction of antidiuretic hormone may be caused by disorders such as pneumonia and stroke and by drugs such as carbamazepine (an anticonvulsant) and sertraline (an antidepressant). Some drugs, especially nonsteroidal anti-inflammatory drugs (NSAIDs), and foods that are high in sodium cause fluids to be retained and may lead to mild overhydration. People who are hospitalized can become overhydrated if they are given intravenous fluids or blood transfusions too rapidly.

Symptoms and Diagnosis

Overhydration often causes swelling in the legs or, if people are confined to bed, in the lower back. However, swelling in the legs is not always caused by overhydration. Often, it is caused or worsened by poor circulation due to a blood vessel disorder (such as chronic venous insufficiency), particularly in people who sit a lot.

Overhydration can cause shortness of breath because fluid backs up in the lungs. Often, shortness of breath is worse when a person lies down, because fluid moves from the feet and legs into the abdomen and chest. The person may wake up shortly after lying down, gasping for air.

If overhydration is suspected, a doctor looks for swelling and enlargement of organs, such as the heart and liver. The veins in the neck are examined to see whether they are overfilled. With a stethoscope, the doctor listens to the heart and lungs for any signs of heart failure.

Other tests may be done to determine whether symptoms are due to overhydration or to poor circulation in the legs. Blood tests may be done to measure levels of electrolytes or other substances that indicate how well the kidneys are functioning. A chest x-ray can show the backup of fluid in the lungs. Tests may be needed to determine whether heart failure is present.

Treatment

For people who are overhydrated, treatment involves helping the body excrete the excess water. Diuretics are drugs that help the kidneys do just that. There are several types of diuretics. Thiazide diuretics are often used first, because they are mild and tend to have few side effects. However, more potent diuretics, such as furosemide, are often needed. Diuretics can be taken by mouth or given intravenously.

Most diuretics cause the kidneys to excrete more potassium as well as more water. Therefore, most people who take diuretics have to take potassium supplements or eat foods rich in potassium. Some people are also given another type of diuretic, which reduces the amount of potassium excreted (potassium-sparing diuretic).

Taking a diuretic can cause or worsen urinary incontinence. Taking a diuretic can also worsen the need to urinate during the night (nocturia). However, a dose of a diuretic can usually be timed so that the diuretic's maximum effect does not occur when a bathroom is unavailable or when a person is sleeping.

If edema due to overhydration is bothersome, support stockings can help reduce the amount of fluid that accumulates in the legs. Consuming less salt also helps. If edema is due to poor circulation rather than overhydration, increasing physical activity can help. Usually, the blood vessel disorder that is causing poor circulation is treated.

If possible, the cause of overhydration is corrected. If the cause was giving intravenous fluids too rapidly, doctors give them more slowly. Heart failure and kidney disorders can be treated. If the cause is a drug, the drug may be discontinued. However, some older people need to take NSAIDs for arthritis or pain. Such people may have to tolerate a small amount of edema or take a diuretic. If the cause of overhydration is overproduction of antidiuretic hormone, the amount of fluids consumed each day may have to be limited.

See the table Types of Diuretics.