creased hydrostatic venous pressure or decreased oncotic venous pressure, due to obstruction of lymphatic or venous vessels draining the lower extremity. Certain drugs (for example, amlodipine) can cause pedal edema.
- Cerebral edema is extracellular fluid accumulation in the brain. It can occur in toxic or abnormal metabolic states and conditions such as systemic lupus or reduced oxygen at high altitudes. It causes drowsiness or loss of consciousness, leading to brain herniation and death.
- Pulmonary edema occurs when the pressure in blood vessels in the lung is raised because of obstruction to the 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. Affected people may perceive coloured haloes around bright lights.
- Edema surrounding the eyes is called periorbital edema (puffy eyes) . The periorbital tissues are most noticeably swollen immediately after waking, perhaps as a result of 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, 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 caused by an increased tendency of the tissue to hold water within its extracellular space. In myxedema, this is due to an increase in hydrophilic carbohydrate-rich molecules (perhaps mostly hyaluronin) 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. 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.
A rise in hydrostatic pressure occurs in cardiac failure. A fall in osmotic pressure occurs in nephrotic syndrome and liver failure.
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. Such severe systemic edema is called anasarca. In rare cases, a parvovirus B19 infection may cause generalized edemas.
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. Most forms of nephrotic syndrome are due to biochemical and structural changes in the basement membrane of capillaries in the kidney glomeruli, and these changes occur, if to a lesser degree, in the vessels of most other tissues of the