Oedema is abnormal fluid accumulation in body tissues that may be localized (as in swelling from an injury) or generalized (as in heart failure ).
Water balance in the body
Water accounts for roughly three fifths of body weight and is constantly exchanged between blood and tissues. The pressure of blood being pumped around the body forces water out of the capillaries (tiny blood vessels) and into the tissues. By a reverse process, which depends on the water-drawing power of the proteins in the blood (osmosis ), water is reabsorbed into the capillaries and lymphatic vessels from the tissues. Normally, these two mechanisms are in balance, keeping the distribution of water between the blood and tissues more or less constant.
The action of the kidneys and hormones, including antidiuretic hormone (ADH), regulate the total amount of fluid in the body. Any excess is excreted from the body as urine.
Causes of oedema
Various disorders can disrupt these processes. Heart failure leads to congestion in the veins, which creates backward pressure in the capillaries.This overcomes osmotic pressure in the capillaries and causes more fluid than normal to be forced into the tissues. Backward pressure can also be created by a tumour pressing on veins, causing oedema in the area drained by the obstructed vein.
In nephrotic syndrome, an abnormal loss of protein from the blood reduces osmotic pressure and prevents enough fluid being drawn from the tissues into the blood. Kidney failure prevents salt being excreted from the body, allowing it to accumulate in the tissues and attract water to it. Other disorders that can cause oedema include cirrhosis of the liver, which leads to blood congestion in the veins of the liver, lowers blood protein (and therefore osmotic pressure), and causes salt retention. A deficiency of protein in the diet, as may occur in alcoholics, can also reduce osmotic pressure.
Injury or inflammation may lead to oedema by causing capillaries to leak. The blockage of lymphatic vessels may result in lymphoedema. Oedema may also be caused by certain drugs, such as corticosteroid drugs , that have an action on the kidneys, resulting in salt retention.
Symptoms of generalized oedema, such as swelling around the base of the spine (in bedridden people) or in the ankles, occur when excess body fluid increases by more than 15 per cent. In severe cases, fluid accumulates in large body cavities, such as the peritoneal cavity of the abdomen in ascites or the pleural cavity of the lungs in pleural effusion. In pulmonary oedema, the air sacs of the lungs become waterlogged, causing breathlessness.
The underlying cause of the oedema should be remedied. If this is not possible, symptoms can be relieved by excretion of the excess fluid. Output of urine by the kidneys is increased by restricting dietary salt and by the use of diuretic drugs .
Lymphoedema is an abnormal accumulation of lymph in the tissues, which occurs when the normal drainage of lymph is disrupted (see lymphatic system).
There are various possible causes for lymphoedema. Cancer can lead to the condition if the vessels become blocked by deposits of cancer cells. Surgical removal of lymph nodes under the arm (as in radical mastectomy) or in the groin, or radiotherapy to an area containing lymph nodes, may also result in lymphoedema. In the tropical disease filariasis, the lymphatic vessels may be blocked by parasitic worms. Rarely, the condition is due to a congenital abnormality of the lymphatic vessels known as Milroy’s disease. In addition, lymphoedema may occur for no known reason.
Lymphoedema causes painless swelling in the tissues and thickening of the skin over the affected area. It usually develops in the legs; the swelling may start at the ankle and extend up the leg, and may occur to an incapacitating degree in some individuals. If a limb that is affected by lymphoedema is subsequently injured, infection can easily enter the site of injury and spread rapidly through the body tissues.
There is no known cure for lymphoedema. Treatment consists of taking diuretic drugs, wearing an elastic bandage or compression sleeve, massage, and special exercises; these measures may bring about some improvement.