Edema, (alternate spelling: oedema) formerly referred to as dropsy or hydropsy, is the swelling of the body's tissues due to excess interstitial fluid retention. Edema can occur locally, often affecting the extremities (peripheral edema), or generally, affecting the entire body (anasarca).
In the body, there are two main compartments between which fluid is exchanged: the intravascular and extravascular compartments. Intravascular compartments include the cardiac chambers and the vascular system itself, whereas the extravascular compartments include everywhere else. Fluid moves easily between these compartments, and the extent of this movement is determined primarily by the balance between hydrostatic and oncotic pressures.
Hydrostatic pressure refers to the pressure exerted by gravity on a fluid at equilibrium, and tends to cause fluid to filter out into the extravascular compartment. Oncotic pressure is a form of osmotic pressure in which proteins in the plasma pull fluid back into the intravascular compartment. Typically these pressures are balanced relatively equally, with a net filtration into the extravascular compartment of about 1% of the plasma. The lymphatic system then transports this extra fluid back into the intravascular compartment through the thoracic duct. Therefore, any change in the balance of these pressures that results in a net filtration greater than the lymphatic system can effectively transport can cause edema.
In addition to pronounced swelling, typically the overlying skin will have a stretched, shiny appearance. In cases of pitting edema, the skin over the affected area will retain a distinct dimple for 10 to 15 seconds after being depressed. In patients with peripheral edema, the swelling is often worst after extended periods of sitting or standing. Anasarca, or general edema, will present with swelling covering the entire body. Ascites refers specifically to fluid retention in the peritoneal cavity, and results in distinct swelling of the abdomen.
An increase in hydrostatic pressure can occur as a result of heart failure, kidney failure, liver failure or venous obstruction. Decreased oncotic pressure occurs in patients with malnutrition resulting in an abnormally low level of blood proteins. In addition, any conditions affecting the permeability of vascular membranes, including inflammation or tissue trauma, can also cause more fluid to "leak" out of the intravascular compartment. When the body notices that this leaking is happening, the kidneys in turn retain more water and sodium to make up for the loss of fluid, causing more blood to circulate and more leakage to occur. Edema related specifically to the impairment of the lymphatic system in carrying away interstitial fluid is referred to as a lymphedema.
Edema itself is not a disease, but a symptom. Less severe forms of edema can result from lifestyle and general health factors such as:
Edema can also occur as a side effect of several different medications, including:
However, edema can also be a sign of severe underlying medical conditions, such as:
If left unchecked, peripheral and general edema can result in the overlying skin becoming stretched, developing infections or ulcerating. Also, decreased blood circulation can lead to blood clots in the deep veins of the body, also known as deep vein thrombosis.
Depending on diagnosis, the following precautions may help minimize the risk of developing edema in at-risk patients and to minimize complications in patients already exhibiting symptoms:
Treating edema should always begin with diagnosing and treating the underlying cause. Depending on the cause, diuretics may be prescribed to increase water output from the kidneys and combining these with a low-sodium diet can help to decrease fluid retention. Other medications and treatments may be prescribed as well. Peripheral edema can also be treated by wearing prescribed compression stockings or garments, which apply more pressure to the affected area and can help force fluid to be reabsorbed into the intravascular compartment.
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