Pleural Effusion in Cats: What You Need to Know

If your cat is having difficulty breathing, it's important to take them to the veterinarian as soon as possible. One of the potential causes of this breathing difficulty could be pleural effusion. In this article, we will discuss what pleural effusion is, what causes it, and how it is treated. We will also cover some common symptoms of pleural effusion in cats so that you can be aware of them if your cat exhibits them.

What is the pleural space in cats?

The pleura is a thin membrane that contains blood vessels and lymphatics. The parietal pleura covers the chest wall, and the visceral pleura covers the lung surface. Between these two layers is the pleural space - a potential space normally filled with small amounts of fluid (1-2 mls in the average-sized cat). The easiest way of thinking of it is the pleural space is between the chest wall and the lungs.

What is pleural effusion in cats?

Pleural effusion is the accumulation of excessive amounts of fluid within the pleural space. If the fluid production by the parietal pleura exceeds the fluid resorption by the visceral pleura, a build-up of fluid will occur between these two layers of tissue, resulting in pleural effusion.

There are many different fluid types that can make up pleural effusion: Transudates, exudates, and chylous effusions are examples.

Transudate

Pure transudate is a clear, colorless fluid. Pure transudates form when there is a decrease in the oncotic pressure of blood caused by low levels of proteins (hypoproteinemia). Diseases that can result in hypoproteinemia include protein-losing enteropathy, protein-losing nephropathy, and liver disease.

Modified transudate

A modified transudate is similar to a pure transudate although the cellular and protein counts are much higher. Modified transudates usually form when the hydrostatic pressure inside the chest increases or when the lymphatic drainage decreases. Causes of modified transudates include heart disease, cancer, lung lobe torsion, pericardial effusion, and liver disease.

Exudate

Exudates have a higher protein concentration and cell count than pure or modified transudates. They often appear turbid, opaque, white, yellow, or red. The fluid can be thick and viscous with a foul odor. Causes of exudates include feline infectious peritonitis (FIP), pneumonia, penetrating thoracic wounds, pancreatitis, and cancer.

Chylous

Chylous effusions are usually whitish and opaque with a high triglyceride concentration. They occur when there is a disruption to the thoracic duct, which is responsible for carrying lymph from the body back into circulation. Causes of chylous effusions include trauma, lymphangiectasia, neoplasia and heart disease.

What are the symptoms of pleural effusion in cats?

The most common clinical symptoms of pleural effusion in cats include:

• Increased respiratory rate (tachypnea)
• Shallow breathing with increased effort
• Open-mouth breathing
• Coughing

As the condition progresses and becomes chronic, cats can have symptoms such as lethargy, weight loss, decreased appetite, and vomiting.

What are the most common causes of pleural effusion in cats?

The most common causes of pleural effusion in cats are congestive heart failure (CHF), feline infectious peritonitis (FIP), cancer, chylothorax, and bacterial infection. In one study, these causes accounted for more than 88% of cases with pleural effusion.

Congestive heart failure (CHF)

One of the most common causes of pleural effusion in cats is congestive heart failure (CHF). CHF occurs when the heart cannot pump blood efficiently around the body. This results in a build-up of fluid in various tissues, including the pleural space. Cats with CHF often have pleural effusions on both sides of the chest.

Feline infectious peritonitis (FIP)

Feline infectious peritonitis (FIP) is a viral disease that can affect cats of all ages. It is most commonly seen in young adult cats between six months and three years old.

Cancer

Cancer is another common cause of pleural effusion in cats. pleural effusions are often seen with metastatic cancer, where cancer has spread from its original site to other parts of the body. Cancer that originates in the pleural space, such as mesothelioma, can also cause pleural effusions.

Chylothorax

Chylothorax is the accumulation of lymphatic fluid in the pleural space. It occurs when there is a disruption to the thoracic duct, which is responsible for carrying lymph from the body back into circulation. Chylothorax can be caused by various conditions, including trauma, neoplasia, and heart disease.

Bacterial infection

Bacterial infections are another common cause of pleural effusion in cats. Infections that commonly cause pleural effusions include pneumonia, pyothorax (a chest infection), and pleurisy (inflammation of the pleural membrane).

How is pleural effusion diagnosed in cats?

Your veterinarian will first start with a detailed physical examination. The breathing pattern of your cat will be examined, as well as the chest auscultated. Pleural effusion will usually make the lung sounds very difficult to hear with the stethoscope as the fluid interferes with the sound acoustics.

If your cat is stable, X-rays of the chest will be taken. Chest X-rays can be used to detect pleural effusion. Performing radiographs on a cat with respiratory distress prior to treatment has been associated with increased mortality.

Assessment of the type of pleural effusion present is diagnosed by taking a sample of the fluid and sending it to a laboratory for analysis (thoracocentesis). The most common way to collect pleural fluid is by needle aspiration, which involves inserting a needle into the pleural space and withdrawing fluid.

Once the fluid has been collected, it will be examined for cell counts and protein concentration. The results will then reveal the classification/type of pleural effusion.

What are the treatment options for pleural effusion in cats?

The treatment of pleural effusion in cats will depend on the underlying cause. In many cases, treating the underlying condition will resolve the pleural effusion. For example, pleural effusions caused by congestive heart failure can often be resolved with treatment of the heart disease.

In some cases, pleural effusion may need to be drained. This can be done by needle aspiration or thoracocentesis (a procedure where the pleural fluid is drained).

Pleural effusion caused by chylothorax can be treated with a low-fat diet and mild diuretic therapy. If this does not resolve the effusion, then surgery may be required to repair the thoracic duct.

Cats with pleural effusions caused by cancer may require aggressive treatment, including surgery, chemotherapy, and radiation therapy.

What is the prognosis for pleural effusion in cats?

The prognosis for pleural effusion in cats will depend on the underlying cause. In many cases, the pleural effusion can be resolved with treatment of the underlying condition. However, in some cases, pleural effusion may be a sign of a more serious condition and can lead to respiratory distress and death. If your cat has pleural effusion, it is important to have them seen by a veterinarian as soon as possible.

Have you ever noticed your cat coughing or having difficulty breathing? These could be signs of pleural effusion, which is the accumulation of fluid in the pleural space. Pleural effusion can be caused by many different conditions, including congestive heart failure, cancer, and bacterial infections. Treatment of pleural effusion will depend on the underlying cause. If you think your cat may have pleural effusion, it is important to have them seen by your veterinarian as soon as possible.