EDEMA

WHAT IS EDEMA?
Edema (American English) or oedema (British English; both words from the Greek οἴδημα, oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body. 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
CLASSIFICATION

Generalized
A rise in hydrostatic pressure occurs in cardiac failure. A fall in osmotic pressure occurs in nephrotic syndrome and liver failure. It is commonly thought that these facts explain the occurrence of edema in these conditions. However, it has been known since the 1950s that the situation is more complex and it is still far from completely understood.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 pulmonary edema, pleural effusions, ascites and peripheral edema.Although a low plasma oncotic pressure is widely cited for the edema of nephrotic syndrome, most physicians note that the edema may occur before there is any significant protein in the urine (proteinuria) or fall in plasma protein level. Fortunately there is another explanation available. Most forms of nephrotic syndrome are due to biochemical and structural changes in the basement membrane of capillaries in the kidney glomerulae, and these changes occur, if to a lesser degree, in the vessels of most other tissues of the body. Thus the resulting increase in permeability that leads to protein in the urine can explain the edema if all other vessels are more permeable as well.
 WHAT THE ORGAN SPECIFIC WILL INVOLVE?
Edema will occur in specific organs as part of inflammation, as in pharyngitis, tendonitis or pancreatitis, for instance. Certain organs develop edema through tissue specific mechanisms.
Examples of edema in specific organs:Cerebral edema is extracellular fluid accumulation in the brain. It can occur in toxic or abnormal metabolic states and conditions such as systemic lupus. It causes drowsiness or loss of consciousness.Pulmonary edema occurs when the pressure in blood vessels in the lung is raised because of obstruction to removal of blood via the pulmonary veins. This is usually due to failure of the left ventricle of the heart. It can also occur in altitude sickness or on inhalation of toxic chemicals. Pulmonary edema produces shortness of breath. Pleural effusions may occur when fluid also accumulates in the pleural cavity.Edema may also be found in the cornea of the eye with glaucoma, severe conjunctivitis or keratitis or after surgery. It may produce coloured haloes around bright lights.
Edema surrounding the eyes is called periorbital edema or eye puffiness. The periorbital tissues are most noticeably swollen immediately after waking, perhaps due to the gravitational redistribution of fluid in the horizontal position.Common appearances of cutaneous edema are observed with mosquito bites, spider bites, bee stings (wheal and flare), and skin contact with certain plants such as Poison Ivy or Western Poison Oak,[2] the latter of which are termed contact dermatitis.Another cutaneous form of edema is myxedema, which is caused by increased deposition of connective tissue. In myxedema (and a variety of other rarer conditions) edema is due to an increased tendency of the tissue to hold water within its extracellular space. In myxedema this is because of an increase in hydrophilic carbohydrate-rich molecules (perhaps mostly hyaluronan) deposited in the tissue matrix. Edema forms more easily in dependent areas in the elderly (sitting in chairs at home or on aeroplanes) and this is not well understood. Estrogens alter body weight in part through changes in tissue water content. There may be a variety of poorly understood situations in which transfer of water from tissue matrix to lymphatics is impaired because of changes in the hydrophilicity of the tissue or failure of the 'wicking' function of terminal lymphatic capillaries.In lymphedema abnormal removal of interstitial fluid is caused by failure of the lymphatic system. This may be due to obstruction from, 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). It is most commonly due to a failure of the pumping action of muscles due to immobility, most strikingly in conditions such as multiple sclerosis, or paraplegia. Lymphatic return of fluid is also dependent on a pumping action of structures known as lymph hearts. It has been suggested that the edema that occurs in some people following use of aspirin-like cyclo-oxygenase inhibitors such as ibuprofen or indomethacin may be due to inhibition of lymph heart action.
Six factors can contribute to the formation of edema:

1.It may be facilitated by increased hydrostatic pressure or,
2.reduced oncotic pressure within blood vessels;
3.increased tissue oncotic pressure
4.by increased blood vessel wall permeability as in inflammation;
5.by obstruction of fluid clearance via the lymphatic system; or,
6.by changes in the water retaining properties of the tissues themselves. Raised hydrostatic pressure often reflects retention of water and sodium by the kidney.[3]