Oedema is another description of a state of abnormal fluid balance. An oedema is an accumulation of fluid in the interstitium which may cause the entire surrounding tissue to swell. This occurs when factors are present that prevent the return of lymph fluid into the blood, or increases fluid loss from the blood. For example, hydrostatic pressure can cause oedema. Another example of a condition that can cause oedema to form are heart defects; whereby the heart is unable to pump enough blood quickly enough, and blood collects in the veins, causing blood pressure to increase to the extent that plasma is forced out of the blood vessels and into the interstitia. Similarly, oedema can occur if you sit or stand still for long periods of time. Increased permeability of such capillaries can also incite oedema. This may occur, for example, in inflammatory reactions.