It refers to excessive accumulation of fluid in tissue spaces caused by disturbance in the fluid interchange between capillaries, tissue spaces and lymphatic vessels.
Etiology: Edema may be due to increase in the hydrostatic pressure or decrease in the osmotic pressure of blood. Any obstruction to the lymphatic drainage or damage to the capillary walls may result in edema. Hydrostatic pressure increases when there is congestive heart failure or there is compression of mammary veins by a foetus. Hepatic fibrosis also leads to ascites. Blood loss due to parasites such as Haemonchus, Fasciola sp., Bunostomum sp. or protein loss due to renal diseases decreases osmotic pressure. It may also occur in hypoproteinemia due to protein deficient diet or liver damage. Lymphatic drainage may be blocked in obstruction, inflammatory swelling, tumor growth or vascular damage as seen in allergic edema. Toxic damage caused by anthrax, gas gangrene and viral arteritis also causes edema.
Clinical signs: Oedematous swellings are soft, painless and pits on pressure. Accumulation of fluid in different cavities may result in ascites, anasarca, hydrothorax and hydropericardium. Heart and respiratory sounds are dull. There is loss of appetite and anaemia.
Diagnosis: Examination of fluid from oedematous swelling reveals absence of inflammatory cells, and the protein content is quite variable.
Treatment: The primary cause of the edema should be ascertained and treatment of the primary cause is required for cure. Use of diuretics and regulation of sodium and water intake are undertaken to manage edema. Peritoneal fluid may be removed through paracentesis, however large quantity of fluid should not be removed suddenly to avoid shock. High quality protein diet should be provided to the affected animal, and digitalization is recommended in myocardial asthenia as seen in congestive heart failure.