Official topic review from UpToDate ® , the clinical information service on the web, CD-ROM and Pocket PC. To subscribe to UpToDate ®

WHAT IS EDEMA? ? Edema means swelling in the small spaces that surround the body tissues and organs. Edema can occur nearly anywhere in the body. The location of the edema will depend, in part, on the underlying cause. Some of the most common sites are:

Pulmonary edema can be life-threatening. In comparison, ascites and peripheral edema can produce some discomfort and cosmetic concerns, but are generally not serious although the underlying cause of edema may be.

WHAT CAUSES EDEMA? ? In most cases, the process of edema formation begins when fluid leaks from the body's smallest blood vessels, called capillaries, into the surrounding tissues. The leakage can occur because of changes in pressure in the capillaries, weakening of the capillary wall from disease, or other factors.

Usually, the leakage itself is not enough to cause noticeable edema. However, when the body senses that fluid is being lost from the capillaries, it signals the kidneys to hold on to sodium and water. This results in an increase in the volume of fluid circulating in the blood vessels, which, in turn, leads to additional leakage of fluid from the capillaries. It is typically at this point that edema can be seen.

CONDITIONS ASSOCIATED WITH EDEMA ? A number of different problems can produce these conditions and cause edema to occur. Some of the most common are conditions unrelated to any specific disease. For example, damage to the veins in the legs (venous insufficiency) can cause abnormal pooling or clotting of blood in these vessels, leading to edema. Pregnancy, drug effects, and problems with drainage in the lymphatic system can also cause peripheral edema. Diseases commonly associated with edema are kidney disease, heart failure, and cirrhosis of the liver.

Venous insufficiency ? A common cause of peripheral edema in clinical practice is venous insufficiency, one cause of which is a syndrome that may occur after an episode of venous blood clots (called deep vein thrombosis). The edema is usually limited to the lower extremities and may be unilateral, a finding that is not seen in those with other conditions.

Pregnancy ? Pregnant women retain a significant amount of sodium and water. Some of this excess fluid is required by the fetus and placenta, but mild edema is also commonly seen.

Drugs ? Edema can be a side effect of a wide variety of medications.

Kidney disease ? The edema of kidney disease, which causes swelling in the legs and around the eyes, is caused by an increase in pressure in the blood vessels that occurs when the kidneys fail to excrete the normal amount of sodium and fluid. The extra fluid exerts pressure on the blood vessel walls, setting up the conditions for edema. In addition, low levels of the albumin in the blood in some people with kidney disease may also contribute to the leakage of fluid from the capillaries.

Heart failure ? In heart failure, also called congestive heart failure, the heart is weakened and its pumping action is impaired. It can affect the right heart chambers, which receive blood from the body and pump it to the lungs to be filled with oxygen; or it can affect the left heart chambers, which pump oxygenated blood to the rest of the body.

Heart failure develops as a result of other conditions that damage the heart. These include heart attacks due to coronary heart disease, diseases of the heart valves, and hypertension (high blood pressure).

In right heart failure, pressure builds in the right chambers because they fail to pump blood efficiently. The pressure is reflected back to the blood vessels in the body that lead to the right chambers, frequently causing peripheral edema and, sometimes, ascites. The patient therefore notices swelling in the legs and abdomen, as well as other symptoms.

In left heart failure, pressure builds in the left chambers because they are failing to pump blood efficiently. This time, the increased pressure is reflected in the large blood vessels that connect the left side of the heart with the lungs. This causes edema in the lungs, or pulmonary edema, and the patient feels shortness of breath.

Some patients have heart failure in both the left and right chambers; others have primarily one or the other.

Cirrhosis ? With cirrhosis, congestion in the liver leads to an increase in pressure within the blood vessels in the liver and, subsequently, in the blood vessels leading into the liver, causing ascites. The patient may have pronounced swelling in the abdomen, as well as edema in the feet or, if the patient is lying down most of the day, swelling in the lower back (also called sacral edema).

HOW DOES MY DOCTOR KNOW WHAT IS CAUSING MY EDEMA? ? The doctor uses a number of different tools to determine the likely cause for edema. For example, close examination of the legs and veins in the neck provide valuable clues. By listening to the lungs through a stethoscope or viewing the lungs on x-ray, doctors can detect the presence of fluid that can point to pulmonary edema as a cause. Blood and urine tests give additional information related to kidney or liver disease that may be contributing to edema.

HOW IS EDEMA TREATED? ? Pulmonary edema is the only form of edema that is life-threatening and needs immediate treatment. This is because edema in the lungs can interfere with breathing. In most cases, treatment of other forms of edema can proceed more slowly.

Treatment is directed at the underlying disease, if possible, removing the excess fluid with diuretics, and minimizing further fluid accumulation by restricting sodium intake and other measures.

Diuretics ? Diuretics are medicines that stimulate the kidneys to remove fluid. Diuretics must be used carefully as fluid removal decreases the circulating blood volume. In some patients, this can result in a decrease in blood pressure and other problems.

Although diuretics are beneficial in many types of edema, they are not appropriate in every case. In particular, diuretics are generally not recommended for edema caused by pregnancy, where fluid retention is generally normal, or venous insufficiency.

Restriction of sodium in the diet ? In most cases, the patient is advised to restrict dietary salt and foods containing sodium. Sodium can cause the kidneys to retain more fluid, worsening the edema.

Body positioning ? Leg edema can be improved by elevating the legs and the use of elastic stockings, which can help drain excess fluid.

Other measures ? Many other drugs and/or interventions can be utilized based upon the underlying disease process.

WHERE TO GET MORE INFORMATION ? Your doctor is the best resource for finding out important information related to your particular case. Not all patients with edema are alike, and it is important that your situation is evaluated by someone who knows you as a whole person.

This discussion will be updated as needed every four months on our web site ( http://www.uptodate.com ). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.

A number of other sites on the Internet have information about edema. Information provided by the National Institutes of Health, national medical societies, and some other well-established organizations are often reliable sources of information, although the frequency with which their information is updated is variable.

REFERENCES