Edema is a kind of swelling due to or accumulation of interstitial fluid. Interstitial fluid is a fluid (salt and water) found in the spaces between the cells and it constitutes around 20 percent of the body weight under normal conditions. [1] This percentage is maintained by fluids leaking from the capillaries into the spaces and subsequent removal of interstitial fluid by the lymphatic system. edema occurs when this balance is disturbed because of: Increase in hydrostatic pressure which causes the fluid to filter into the interstitial spaces. Decrease in oncotic pressure that causes the proteins in the fluid to