Edema is observable swelling from fluid accumulation in body tissues. Edema most commonly occurs in the feet and legs, where it is referred to as peripheral edema. The swelling is the result of the accumulation of excess fluid under the skin in the spaces within the tissues. All tissues of the body are made up of cells and connective tissues that hold the cells together.
This connective tissue around the cells and blood vessels is known as the interstitium. Most of the body's fluids that are found outside of the cells are normally stored in two spaces; the blood vessels (as the "liquid" or serum portion of your blood) and the interstitial spaces (not within the cells). In various diseases, excess fluid can accumulate in either one or both of these compartments.
The body's organs have interstitial spaces where fluid can accumulate. An accumulation of fluid in the interstitial air spaces (alveoli) in the lungs occurs in a disorder called pulmonary edema.
In addition, excess fluid sometimes collects in what is called the third space, which includes cavities in the abdomen (abdominal or peritoneal cavity - called "ascites") or in the chest (lung or pleural cavity - called "pleural effusion"). Anasarca refers to the severe, widespread accumulation of fluid in the all of the tissues and cavities of the body at the same time.
What is pitting edema and how does it differ from non-pitting edema?
Pitting edema can be demonstrated by applying pressure to the swollen area by depressing the skin with a finger. If the pressing causes an indentation that persists for some time after the release of the pressure, the edema is referred to as pitting edema. Any form of pressure, such as from the elastic in socks, can induce pitting with this type of edema.
In non-pitting edema, which usually affects the legs or arms, pressure that is applied to the skin does not result in a persistent indentation. Non-pitting edema can occur in certain disorders of the lymphatic system such aslymphedema, which is a disturbance of the lymphatic circulation that may occur after a mastectomy, lymph node surgery, or congenitally.
Another cause of non-pitting edema of the legs is called pretibial myxedema, which is a swelling over the shin that occurs in some patients with hyperthyroidism. Non-pitting edema of the legs is difficult to treat. Diuretic medications are generally not effective, although elevation of the legs periodically during the day and compressive devices may reduce the swelling.
The focus of the rest of this article is on pitting edema, as it is by far the most common form of edema.
Symptoms of peripheral edema include swelling of the affected area(s), which causes the surrounding skin to "tighten". The swelling from peripheral edema is gravity-dependent (it will increase or decrease with changes in body position).
For example, if a person is lying on their back (supine), the swelling will not appear in the legs, but will appear in the area around the sacrum. The skin over the swollen area appears tight and shiny, and often when pressure is applied to the area with a finger, an indentation appears. This is called pitting edema.
In the case of pulmonary edema, there is often no evidence of fluid retention or noticeable swelling on examination of the patient's extremities. This is because the fluid is backing up into the lungs.
Signs and symptoms of pulmonary edema include:
- shortness of breath,
- difficulty breathing when lying flat,
- waking up breathless,
- requiring multiple pillows to raise the head at night for a comfortable sleep.
The balance and regulation of fluid in the body is very complex. In short, the cause of edema as simply defined as possible, is that tiny blood vessels in the body (capillaries) leak fluid into the surrounding tissues. This excess fluid causes the tissues to swell.
The cause of fluid leaking into the surrounding tissues may be the result of several mechanisms, for example:
- too much force, or pressure inside the blood vessels;
- a force outside of the blood vessel causes the fluid to be drawn through it;
- the wall of the blood vessel is compromised and cannot maintain equilibrium.
Each of these three mechanisms may be associated with a variety of diseases or conditions. Examples include the following:
- Pregnancy: Edema during pregnancy may occur because pregnant women have a greater volume of fluid circulating in the body, and because they also retain more fluid. A woman may also experience postpartum edema.
- Medications: Edema may be caused by a variety of medications, for example, steroids, calcium channel blockers (CCBs), thiazolidinediones,nonsteroidal antiinflammatory drugs (NSAIDs), estrogens, etc.).
- Liver disease and/or kidney disease: Both of these organs are vital in maintaining fluid balance in the body, and if severe disease is present in either of these organ systems, edema can develop. Examples include: cirrhosis of the liver, chronic kidney disease, and acute kidney failure.
- Venous insufficiency: This is a common condition in which blood does not return to the heart efficiently from the peripheral areas of the body (for example, the ankles, legs, feet, hands), which results in edema. This typically results in edema in both legs.
- Heart failure: If the heart is weak and cannot pump blood efficiently, blood will pool in particular areas of the body, which will cause fluid to leak from the blood vessels into the surrounding tissues.
- If the right side of the heart is weak, pressure will build in the peripheral tissues in the body (hands, ankles, feet, legs). This is referred to as peripheral edema.
- If the left side of the heart is weak, pressure will build in the lungs, causing pulmonary edema.
- Idiopathic edema: Accumulation of fluid in surrounding tissues with no identifiable cause is referred to as idiopathic edema.
Compression stockings can be helpful by increasing the resistance to fluid leaking out of the vessels. These can be purchased in any medical supply store, and are particularly useful for peripheral edema. Body positioning can also be helpful for both peripheral and pulmonary edema to ease symptoms. For example, elevating the head with pillows in bed may benefit someone with pulmonary edema, while elevating the legs may minimize ankle and/or leg edema.
Once again, the treatment depends on the condition causing edema. In general, the treating principle is to reverse the forces that are not working properly:
- Increase the forces that keep fluid inside the blood vessels.
- Reduce the forces that cause fluid to leak out of the blood vessels.
- Identify the cause of the leaking blood vessel walls.
For example, increasing the blood protein (albumin) level in a patient with a nutritional deficiency can help retain fluid in the blood vessels. Healing tissues exposed to trauma, (for example, swelling from a sprained ankle) assists in preventing fluid leaking from blood vessels.
The ultimate goal with edema treatment is to rid the excess fluid that has accumulated in the surrounding tissues in the body. The most common treatment is a diuretic. Diuretics make the kidneys excrete excess fluid from the body; which reduces the general fluid volume in the body. Diuretics should be used with caution asdehydration can be a side effect. There are many different types of diuretics that have different mechanisms of action and different potencies.