Pleural effusion is not really a disease entity in itself; rather, it is a sign of disease. It occurs more frequently in cats than it does in dogs. The pleural space is an air-filled space located in the thoracic cavity between the inner thoracic wall and the thoracic organs themselves.
Pleural effusion is a buildup of fluid—such as blood, pus, or serum— within this pleural space. This effectively interferes with the normal functioning of the heart and lungs. Some of the potential causes of pleural effusions include infectious diseases (bacterial and fungal infections, FIP, feline leukemia), foreign bodies within the chest, rupture of lymphatic vessels, heart disease, or cancer.
Pets afflicted with a pleural effusion must fight for every breath, often exhibiting open-mouthed breathing with their necks extended forward. In severe instances, they can collapse from lack of oxygen.
Emergency treatment is a must. If pleural effusion is present, treatment will involve drainage of the fluid from the chest. This usually entails placement of a temporary drain tube within the chest to facilitate continued drainage as it is required until the exact cause of the problem can be discerned.
The nature of the fluid removed from the pleural space will usually afford the veterinarian enough information to pinpoint the exact cause of the effusion. Treatment is then directed accordingly.