Oedema is a PHYSICAL SIGN which points to an underlying local or systemic disease and may be visible or palpable as localised or generalised swelling or be hidden and detectable only on further examination and testing. It occurs when the normal mechanisms for maintaining a balance between fluid in the tissues and in the blood are upset. That balance depends mainly on the blood pressure that keeps blood flowing through the circulatory system – thus forcing fluid out of the capillaries – and the osmotic drawing force of the blood proteins which pulls water into the bloodstream. The KIDNEYS also have an essential role in maintaining this balance.

Among the disorders that may disturb this balance are heart failure, NEPHROTIC SYNDROME, kidney failure, CIRRHOSIS of the liver and a diet deficient in protein. Injury may also cause oedema and ascites (fluid in the abdominal cavity) can occur as a result of cirrhosis of the liver or cancer in the abdominal organs. In a pregnant woman, oedema of the feet and ankles may be a sign of PRE-ECLAMPSIA.

The underlying cause of oedema should be treated and, if this is not feasible or effective, the excess fluid should be excreted by boosting the output of the kidney. Restriction of sodium in the diet and the administration of DIURETICS are effective methods of achieving this.