y (such as inflammation);
- obstruction of fluid clearance in the lymphatic system;
- changes in the water-retaining properties of the tissues themselves. Raised hydrostatic pressure often reflects retention of water and sodium by the kidneys.
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 colloidal or oncotic pressure of the higher level of protein in the plasma tends to draw 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 venules, 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 edemas 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 colloidal or oncotic pressure difference by allowing protein to leave the vessel more easily.
Another set of vessels known as the lymphatic system acts like an "overflow" and can return much excess fluid to the bloodstream. But even the lymphatic system can be overwhelmed, and if there is simply too much fluid, or if the lymphatic system is congested, then the fluid will remain in the tissues, causing swellings in legs, ankles, feet, abdomen or any other part of the body.
|+||Mild: Both feet / ankles|
|++||Moderate: Both feet,|
plus lower legs,
hands or lower arms
bilateral pitting edema,
including both feet,
legs, arms and face
Edema may be described as pitting edema, or non-pitting edema.Pitting edema is when, after pressure is applied to a small area, the indentation persists after the release of the pressure. Peripheral pitting edema, as shown in the illustration, is the more common type, resulting 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 veins, thrombophlebitis, insect bites, and dermatitis.
Non-pitting edema is observed when the indentation does not persist. It is associated with such conditions as lymphedema, lipedema, and myxedema.
Edema caused by malnutrition defines kwashiorkor, an acute form of childhood protein-energy malnutrition characterized by edema, irritability, anorexia, ulcerating dermatoses, and an enlarged liver with fatty infiltrates.
When possible, treatment involves resolving the underlying cause. Many cases of heart or kidney disease are treated with diuretics.
Treatment may also involve positioning the affected body parts to improve drainage. For example, swelling in feet or ankles may be reduced by having the person lie down in bed or sit with the feet propped up on cushions. Intermittent pneumatic compression can be used to pressurize tissue in a limb, forcing fluids—both blood and lymph—to flow out of the compressed area.
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Causes and signs of edema. Institute for Quality and Efficiency in Health Care (IQWiG). 2016. https://www.ncbi.nlm.nih.gov/books/NBK279409/.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 "Edema - Cardiovascular Disorders". https://www.merckmanuals.com/professional/cardiovascular-disorders/symptoms-of-cardi