Edema
Encyclopedia
Edema or oedema (British English
); both words from the Greek , 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 that produces 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.
, thrombophlebitis
, insect bites, and dermatitis
.
Non-pitting edema is observed when the indentation does not persist. It is associated with such conditions as lymphedema
, lipoedema and myxedema
.
Edema caused by malnutrition defines kwashiorkor
.
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.
or pancreatitis, for instance. Certain organs develop edema through tissue specific mechanisms.
Examples of edema in specific organs:
Generation of interstitial fluid is regulated by the forces of the Starling equation
. Hydrostatic pressure within blood vessels tends to cause water to filter out into the tissue. This leads to a difference in protein concentration between blood plasma and tissue. As a result the oncotic pressure
of the higher level of protein in the plasma tends to suck water back into the blood vessels from the tissue. Starling's equation states that the rate of leakage of fluid is determined by the difference between the two forces and also by the permeability of the vessel wall to water, which determines the rate of flow for a given force imbalance. Most water leakage occurs in capillaries or post capillary venule
s, which have a semi-permeable membrane wall that allows water to pass more freely than protein. (The protein is said to be reflected and the efficiency of reflection is given by a reflection constant of up to 1.) If the gaps between the cells of the vessel wall open up then permeability to water is increased first, but as the gaps increase in size permeability to protein also increases with a fall in reflection coefficient.
Changes in the variables in Starling's equation can contribute to the formation of edema either by an increase in hydrostatic pressure within the blood vessel, a decrease in the oncotic pressure within the blood vessel or an increase in vessel wall permeability. The latter has two effects. It allows water to flow more freely and it reduces the oncotic pressure difference by allowing protein to leave the vessel more easily.
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...
); both words from the Greek , 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 that produces swelling
Swelling (medical)
In medical parlance, swelling is the transient enlargement or protuberance in the body and may include tumors. According to cause, it may be congenital, traumatic, inflammatory, neoplastic or miscellaneous....
. Generally, the amount of interstitial fluid
Interstitial fluid
Interstitial fluid is a solution that bathes and surrounds the cells of multicellular animals. It is the main component of the extracellular fluid, which also includes plasma and transcellular fluid...
is determined by the balance of fluid homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
, and increased secretion of fluid into the interstitium or impaired removal of this fluid may cause edema.
Classification
Cutaneous edema is referred to as "pitting" when, after pressure is applied to a small area, the indentation persists for some time after the release of the pressure. Peripheral pitting edema, as shown in the illustration, is the more common type, results from water retention. It can be caused by systemic diseases, pregnancy in some women, either directly or as a result of heart failure, or local conditions such as varicose veinsVaricose veins
Varicose veins are veins that have become enlarged and tortuous. The term commonly refers to the veins on the leg, although varicose veins can occur elsewhere. Veins have leaflet valves to prevent blood from flowing backwards . Leg muscles pump the veins to return blood to the heart, against the...
, thrombophlebitis
Thrombophlebitis
Thrombophlebitis is phlebitis related to a thrombus . When it occurs repeatedly in different locations, it is known as "Thrombophlebitis migrans" or "migrating thrombophlebitis".-Signs and symptoms:...
, insect bites, and dermatitis
Dermatitis
-Etymology:Dermatitis derives from Greek derma "skin" + -itis "inflammation" and genetic disorder.-Terminology:There are several different types of dermatitis. The different kinds usually have in common an allergic reaction to specific allergens. The term may describe eczema, which is also called...
.
Non-pitting edema is observed when the indentation does not persist. It is associated with such conditions as lymphedema
Lymphedema
Lymphedema , also known as lymphatic obstruction, is a condition of localized fluid retention and tissue swelling caused by a compromised lymphatic system....
, lipoedema and myxedema
Myxedema
Myxedema describes a specific form of cutaneous and dermal edema secondary to increased deposition of connective tissue components in subcutaneous tissue as seen in various forms of hypothyroidism and Graves' disease. It is more common in women than in men...
.
Edema caused by malnutrition defines kwashiorkor
Kwashiorkor
Kwashiorkor is an acute form of childhood protein-energy malnutrition characterized by edema, irritability, anorexia, ulcerating dermatoses, and an enlarged liver with fatty infiltrates. The presence of edema caused by poor nutrition defines kwashiorkor...
.
Generalized
A rise in hydrostatic pressure occurs in cardiac failure. A fall in osmotic pressure occurs in nephrotic syndromeNephrotic syndrome
Nephrotic syndrome is a nonspecific disorder in which the kidneys are damaged, causing them to leak large amounts of protein from the blood into the urine....
and liver failure
Liver failure
Acute liver failure is the appearance of severe complications rapidly after the first signs of liver disease , and indicates that the liver has sustained severe damage . The complications are hepatic encephalopathy and impaired protein synthesis...
. 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
Pulmonary edema
Pulmonary edema , or oedema , is fluid accumulation in the air spaces and parenchyma of the lungs. It leads to impaired gas exchange and may cause respiratory failure...
, pleural effusions, ascites
Ascites
Ascites is a gastroenterological term for an accumulation of fluid in the peritoneal cavity.The medical condition is also known as peritoneal cavity fluid, peritoneal fluid excess, hydroperitoneum or more archaically as abdominal dropsy. Although most commonly due to cirrhosis and severe liver...
and peripheral edema
Peripheral edema
Peripheral edema is the swelling of tissues, usually in the lower limbs, due to the accumulation of fluids.The condition is commonly associated with aging, but can be caused by many other conditions, including congestive heart failure, trauma, alcoholism, altitude sickness, pregnancy,...
.
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
Proteinuria
Proteinuria means the presence of anexcess of serum proteins in the urine. The protein in the urine often causes the urine to become foamy, although foamy urine may also be caused by bilirubin in the urine , retrograde ejaculation, pneumaturia due to a fistula, or drugs such as pyridium.- Causes...
) 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.
Organ-specific
Edema will occur in specific organs as part of inflammations, tendonitisTendonitis
Tendinitis , meaning inflammation of a tendon , is a type of tendinopathy often confused with the more common tendinosis, which has similar symptoms but requires different treatment...
or pancreatitis, for instance. Certain organs develop edema through tissue specific mechanisms.
Examples of edema in specific organs:
- Cerebral edemaCerebral edemaCerebral edema or cerebral œdema is an excess accumulation of water in the intracellular or extracellular spaces of the brain.-Vasogenic:Due to a breakdown of tight endothelial junctions which make up the blood-brain barrier...
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.
- Pulmonary edemaPulmonary edemaPulmonary edema , or oedema , is fluid accumulation in the air spaces and parenchyma of the lungs. It leads to impaired gas exchange and may cause respiratory failure...
occurs when the pressure in blood vessels in the lung is raised because of obstruction to remove 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 effusionPleural effusionPleural effusion is excess fluid that accumulates between the two pleural layers, the fluid-filled space that surrounds the lungs. Excessive amounts of such fluid can impair breathing by limiting the expansion of the lungs during ventilation.-Pathophysiology:...
s 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 puffinessEye puffinessPeriorbital puffiness, also known as "puffy eyes" or swelling around the eyes, refers to the appearance of swelling in the tissues around the eyes, called the orbits. It is almost exclusively caused by fluid buildup around the eyes, or periorbital edema...
. 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 mosquitoMosquitoMosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
bites, spiderSpiderSpiders are air-breathing arthropods that have eight legs, and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...
bites, bee stings (wheal and flare), and skin contact with certain plants such as Poison IvyPoison IvyPoison Ivy is a fictional character, a DC Comics supervillainess who is primarily an enemy of Batman. Created by Robert Kanigher and Sheldon Moldoff, she first appeared in Batman #181 ....
or Western Poison Oak, the latter of which are termed contact dermatitisContact dermatitisContact dermatitis is a term for a skin reaction resulting from exposure to allergens or irritants . Phototoxic dermatitis occurs when the allergen or irritant is activated by sunlight....
.
- Another cutaneous form of edema is myxedemaMyxedemaMyxedema describes a specific form of cutaneous and dermal edema secondary to increased deposition of connective tissue components in subcutaneous tissue as seen in various forms of hypothyroidism and Graves' disease. It is more common in women than in men...
, which is caused by increased deposition of connective tissueConnective tissue"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
. 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 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 lymphedemaLymphedemaLymphedema , also known as lymphatic obstruction, is a condition of localized fluid retention and tissue swelling caused by a compromised lymphatic system....
abnormal removal of interstitial fluid is caused by failure of the lymphatic systemLymphatic systemThe lymphoid system is the part of the immune system comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph unidirectionally toward the heart. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated...
. This may be due to obstruction from, for example, pressure from a cancerCancerCancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
or enlarged lymph nodes, destruction of lymph vessels by radiotherapy, or infiltration of the lymphatics by infection (such as elephantiasisElephantiasisElephantiasis is a disease that is characterized by the thickening of the skin and underlying tissues, especially in the legs and male genitals. In some cases the disease can cause certain body parts, such as the scrotum, to swell to the size of a softball or basketball. It is caused by...
). 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.
- Hydrops fetalisHydrops fetalisHydrops fetalis is a condition in the fetus characterized by an accumulation of fluid, or edema, in at least two fetal compartments. By comparison, hydrops allantois or hydrops amnion are an accumulation of excessive fluid in the allantoic or amniotic space respectively.-Presentation:Locations can...
is a condition of the fetus characterized by an accumulation of fluid, or edema, in at least two fetal compartments.
Mechanism
Six factors can contribute to the formation of edema:- increased hydrostatic pressure;
- reduced oncotic pressureOncotic pressureOncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure exerted by proteins in blood plasma that usually tends to pull water into the circulatory system.Throughout the body, dissolved compounds have an osmotic pressure...
within blood vessels; - increased tissue oncotic pressure;
- increased blood vessel wall permeability e.g. inflammationInflammationInflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
; - obstruction of fluid clearance via the lymphatic systemLymphatic systemThe lymphoid system is the part of the immune system comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph unidirectionally toward the heart. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated...
; - changes in the water retaining properties of the tissues themselves. Raised hydrostatic pressure often reflects retention of water and sodium by the kidney.
Generation of interstitial fluid is regulated by the forces of the Starling equation
Starling equation
The Starling equation is an equation that illustrates the role of hydrostatic and oncotic forces in the movement of fluid across capillary membranes.Capillary fluid movement may occur as a result of three processes:...
. Hydrostatic pressure within blood vessels tends to cause water to filter out into the tissue. This leads to a difference in protein concentration between blood plasma and tissue. As a result the oncotic pressure
Oncotic pressure
Oncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure exerted by proteins in blood plasma that usually tends to pull water into the circulatory system.Throughout the body, dissolved compounds have an osmotic pressure...
of the higher level of protein in the plasma tends to suck water back into the blood vessels from the tissue. Starling's equation states that the rate of leakage of fluid is determined by the difference between the two forces and also by the permeability of the vessel wall to water, which determines the rate of flow for a given force imbalance. Most water leakage occurs in capillaries or post capillary venule
Venule
A venule is a very small blood vessel in the microcirculation that allows deoxygenated blood to return from the capillary beds to the larger blood vessels called veins. Venules range from 8 to 100μm in diameter and are formed when capillaries unite .Venules are blood vessels that drain blood...
s, which have a semi-permeable membrane wall that allows water to pass more freely than protein. (The protein is said to be reflected and the efficiency of reflection is given by a reflection constant of up to 1.) If the gaps between the cells of the vessel wall open up then permeability to water is increased first, but as the gaps increase in size permeability to protein also increases with a fall in reflection coefficient.
Changes in the variables in Starling's equation can contribute to the formation of edema either by an increase in hydrostatic pressure within the blood vessel, a decrease in the oncotic pressure within the blood vessel or an increase in vessel wall permeability. The latter has two effects. It allows water to flow more freely and it reduces the oncotic pressure difference by allowing protein to leave the vessel more easily.