What Causes Pleural Effusion in Cats?

What is pleural effusion?

Pleural effusion, sometimes called ‘water on the lungs’ is a build-up of fluid in the space that surrounds your cat’s lungs. It can cause breathing difficulties, which may be mild to severe depending upon how much fluid has built up and what other problems, if any, are involved.

What Causes Pleural Effusion in Cats? The primary cause of pleural effusion is heart failure but many other causes exist including cancerous or infectious lung disease; chest trauma; inflammatory conditions such as systemic lupus erythematosus (SLE); neoplasia (tumours); congestive heart disease; pericarditis (inflammation of the sac surrounding the heart); hypoproteinaemia (low protein levels in the blood); and as a side effect of certain drugs such as non-steroidal anti-inflammatory agents.

Pleural effusion is very common in aged cats and those with heart disease, cancer or SLE. It’s not uncommon for owners to first notice breathing difficulties when they see their cat struggling to breathe during exertion such as running up the stairs or jumping on and off beds. As difficulty breathing progresses it may be seen at other times also, including when your cat is just lying down quietly. Early warning signs that should prompt you to take your cat to a veterinary surgeon include:

Harsh, laboured breathing – this can indicate advanced difficulty breathing due to fluid build-up in the respiratory tract; Swollen abdomen – your cat may be putting on extra effort to breathe due to fluid in its lungs; Retractions of the skin between the ribs – these are another indicator of fluid build up in the respiratory tract.

Pleural effusion is diagnosed with X-rays that show a cloudy area spreading outwards from the heart into one or both of the pleural cavities. An echocardiogram can also reveal whether there is any leakage of blood through the mitral valve which would indicate congestive heart failure, and provide information about how severe it is.

Blood tests are required to find out why cats develop pleural effusions because they can be due to more than one cause, not all of them having signs you might notice at home. Your vet may take chest X-rays if it’s not already known that your cat has heart disease or cancer .

Pleural effusion is treated with medication (usually furosemide) initially. This flushes out some of the fluid which can make breathing easier for your cat, at least until the other health problems are resolved. If necessary it can be repeated after a couple of weeks.

If there’s no improvement you will need to consider other treatment options including draining the fluid off (a procedure known as ‘thoracocentesis’). Pleural effusion often recurs so follow up treatments and/or monitoring will probably be needed. In time, once your cat’s health problem is being successfully managed, its breathing difficulties should go away and the pleural effusion will be resolved.