Oedema (or Edema in American English), formerly known as dropsy or hydropsy, is the increase of interstitial fluid in any organ — swelling. Generally, the amount of interstitial fluid is determined by the balance of fluid homeostasis, and increased secretion of fluid into the interstitium or impaired removal of this fluid may cause edema.
Edema has five pathophysiologic causes. It can be due to increased hydrostatic pressure, reduced oncotic pressure, lymphatic obstruction, sodium retention, or inflammation.
Generation of interstitial fluid is regulated by the Starling equation
of tissue fluid which states that it depends on the balance of osmotic pressure
and of hydrostatic pressure
which act in opposite directions across the semipermeable capillary
walls. Consequently, anything that increases oncotic pressure outside blood vessels (for example, inflammation
), or reduces oncotic pressure
in the blood (states of low plasma osmolality
, for example, cirrhosis
) will cause edema. Increased hydrostatic
pressure inside the blood vessel (for example, in heart failure
) will have the same effect. If the permeability of the capillary walls increases, more fluid will tend to escape out of the capillary, which can happen when there is inflammation
Abnormal removal of interstitial fluid is caused by obstruction of the lymphatic system. This may be due to, for example, pressure from a cancer or enlarged lymph nodes, destruction of lymph vessels by radiotherapy, or infiltration of the lymphatics by infection (such as elephantiasis).
There are two types: exudate and transudate.
Examples of edema in specific organs:
- *Ascites is effectively edema within the peritoneal cavity
- *Pleural effusions are effectively edema in the pleural cavity
- *Cerebral edema is intracellular or extracellular fluid accumulation in the brain
- *Edema may also be found in the eyes after corrective surgery or procedures of that nature.
Causes of edema which are generalized to the whole body can cause edema in multiple organs and peripherally. For example, severe heart failure can cause peripheral edema, pulmonary edema, pleural effusions and ascites.
Common and usually harmless appearances of cutaneous edema are observed with mosquito bites, bee stings (wheal and flare), and skin contact with certain plants (contact dermatitis).
Edema in plants
Edema in plants is the extended swelling in plant organs caused primarily by an excessive accumulation of water. This occurs since the cell walls are composed of flexible cellulose.
- Cho S, Atwood J (2002). "Peripheral oedema". Am J Med 113 (7): 580–6.