Edema Health Article

Definition

Edema is the medical term for swelling. It is an abnormal retention of fluid in body tissue.

Description

Edema that is visible and localized often accompanies a soft-tissue injury, a sprain, or a fracture. However, it is also a component of generalized retention of fluid such as occurs in congestive heart failure (CHF). By weight, 60% of the human body is composed of water. In a remarkable process that is, under normal circumstances, a nearly perfect balance, water is exchanged between the blood and the tissues. As it circulates blood through the body, the pressure from the heart presses water out of capillaries and into body tissues. Osmotic (water-drawing) properties of certain blood proteins cause this process to reverse and fluid to be reabsorbed from the tissues back into the capillaries. To maintain equilibrium, the kidneys draw off excess fluid and salt, which are then excreted as part of the urine. When fluid is not released from the tissues, the result is edema.

Causes and symptoms

The causes and severity of edema cover a wide spectrum, including:

• mild edema that accompanies female hormone imbalance during the menstrual cycle
• allergies in which the chemical histamine is released by the immune system, resulting in fluid leaking into the tissues, which creates swelling
• injuries that do damage to capillaries, causing fluids to seep out into the tissue and not be reabsorbed by the damaged capillaries
• hormonal imbalance caused by taking certain hormonal medications such as corticosteroids, high estrogen contraceptives, or androgens (male hormones)
• beriberi (vitamin B₁ deficiency) and dietary protein deficiency, often found with malnutrition
• the venous congestion that accompanies cirrhosis of the liver and eventually decreases osmotic pressure
• kidney failure, which eventually allows salts and water to be retained in the tissues rather than being excreted
• nephritic syndrome, a condition in which large amounts of blood protein are lost and the blood loses its ability to draw fluid back out of the tissues
• congestive heart failure, a common condition, especially in the elderly, in which the heart functions less efficiently due to coronary artery disease, high blood pressure, or congenital or disease-caused abnormality in the heart

Other than traumatic injuries or allergic reactions, swelling typically develops quite slowly and often goes unnoticed at its onset. It is estimated that fluid in the body can increase by 15% without being visible. Frequently it is manifested at that point only by an increase in weight. When edema does become apparent, it is usually found in the lower part of the body, in the feet, ankles, legs, and lower back. A finger pressed into edematous skin will leave an imprint that slowly disappears as the fluid again refills that tissue.

Severe edematous conditions can cause fluid to gather in body cavities. Ascites, common with cirrhosis of the liver, is characterized by large amounts of fluid amassing in the peritoneal cavity of the abdomen. When liquid fills the pleural cavity adjacent to the lungs, it is termed pleural effusion; the liquid presses upon the lungs, causing difficulty in breathing. Pulmonary edema, which occurs when air sacs in the lungs become waterlogged, also causes respiratory complications.