Anatomy of the Chest Cavity

The thoracic cavity not only houses both lungs and the animal’s heart, but it is also home to several other vital structures such as main blood vessels, nerves, and the esophagus (a muscular tube that moves food from the mouth to the stomach. These organs are protected from external hazards by the ribs and chest muscles.

The chest cavity is separated from the abdomen by a layer of muscle called the diaphragm. Apart from separating vital abdominal and thoracic organs, the diaphragm also plays an important role in the animal’s breathing.

During inspiration, the diaphragm contracts and increases the area of the chest space to allow the lungs to inflate and take in air. As the animal exhales, the diaphragm relaxes and helps push air out of the lungs. Proper and optimal respiration is achieved through the help of the diaphragm and the ability of the chest cavity to expand and contract to accommodate air.

To further ensure proper inflation of the lungs during inspiration, negative pressure is maintained in the space between the lungs and the chest wall, called the pleural space. This small space also contains clear fluid that acts as a lubricant for the lungs during the respiration process.

Disease conditions affecting the pleural space can result in inefficient lung expansion during respiration and cause breathing problems for the animals. This is commonly encountered in conditions that result in the accumulation of fluid in the pleural space, called thoracic effusions.

What does it mean if a pet has “fluid in their chest”?

Thoracic effusion is defined as the accumulation of different types of fluid in the animal’s pleural space. The pleural space can be filled with a variety of bodily fluids depending on the specific underlying condition.

Physical injuries on the animal’s chest region that puncture the muscle layers can expose the pleural space to the external environment and cause air to fill it up, a condition called pneumothorax. When the air gets inside the pleural space, it disrupts the negative pressure and prevents the lungs from fully expanding during respiration.

Another common problem affecting the chest cavity and the pleural space is a condition called pyothorax. Like other types of thoracic effusion, pyothorax occupies the pleural space which prevents the lungs from inflating properly during respiration, leading to breathing problems that can be fatal if not addressed immediately.

What is pyothorax?

Pyothorax is defined as the accumulation of inflammatory fluid or pus in the animal’s pleural space (area between the lungs and chest wall). Most cases of pyothorax in dogs and cats affect both sides of the chest cavity but occasionally only one side gets filled with pus. Pyothorax is caused by an infection penetrating the thoracic cavity, but in most cases, the source of infection is rarely determined.

In cats, the most common cause of pyothorax is bite wounds. Since a cat’s thoracic wall is relatively thin, any injury or bite on the animal’s chest area may penetrate the thoracic cavity and deposit bacteria into the cat’s pleural space. This will eventually cause an infection and result in pus formation, filling the said thoracic space.

In some cases, the infection may originate externally and find its way into the chest cavity. This occurs when an external abscess is left untreated and results in the rupture of the chest wall, allowing the infection to penetrate the pleural space.

In dogs, the most common cause of pyothorax is the presence of foreign material, usually plant in origin, which makes its way into the chest cavity after being accidentally inhaled. As the foreign material penetrates the pleural spaces and lodges itself, it brings bacteria with it, which causes an infection in the area.

The infection triggers the body’s inflammatory process which leads to the formation of pus, eventually filling up the pleural space and resulting in the formation of pyothorax. Since there’s the involvement of foreign material, treatment and resolution of pyothorax in dogs tends to be more complicated than in cats.

Symptoms of Pyothorax in Dogs and Cats

Pets that have pyothorax will often show signs of breathing difficulties such as rapid, shallow breathing or open-mouth breathing. Affected animals will also show signs of general illness such as weakness, lethargy, pain, and decreased appetite. Since the condition is infectious, pets with pyothorax often present with persistent fever.

The severity of the condition varies depending on the extent of infection and the penetration of the pleural space. Some cases can be successfully treated with medications while more severe cases can be fatal to dogs and cats.

If your pet is showing any of the signs mentioned, coupled with a history of possible chest trauma, an immediate visit to the vet is recommended to rule out the possibility of pyothorax.

Treatment Options for Pets with Pyothorax

The goal of treatment in cases of pyothorax is to remove the pus in the pleural space and control the infection. Your vet may place a chest tube to facilitate drainage of pus from the pleural space. This is usually done in a hospital setting and hospitalization for at least 24 hours is often warranted.

Antibiotic therapy will help control and eliminate the infection in both dogs and cats. In dogs, pyothorax caused by the presence of foreign material may require surgical intervention to remove the cause of infection.

Prognosis is usually good in dogs and cats that receive immediate and appropriate care, but the condition can be fatal if it’s severe or not detected and treated properly in a timely manner.

Read more:

How to Measure Resting Respiratory Rates in Dogs

Canine Infectious Respiratory Disease Complex (CIRDC)

Upper Respiratory Infections in Cats

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