Edema is characterized by an excess of salt and water in the extracellular space, particularly in the interstitium. The level of cell metabolism under this condition decreases due to the decrease of exchanging rate in O2 and nutrients between the circulation and the interstitial fluid. Systemic edema is associated with the cardiac and renal diseases leading to salt retention. Local interstitial edema can occur without overall salt and water retention. It may be associated with the tissue inflammation and the disturbance of lymphatic drainage that affect the capillary permeability and the Starling forces.