Pyothorax in Dogs

By Krista Williams, BSc, DVM; Ernest Ward, DVM

Pyothorax refers to the presence of inflammatory fluid or pus within the chest cavity, which is the area between the lungs and the inner walls of the ribs.

What causes pyothorax?

Pyothorax is usually caused by a bacterial infection in the chest cavity. In most cases, pus is present in both sides of the chest although occasionally only one side will be affected.

The source of the infection is rarely found although possible causes include:

  • penetrating wounds to the chest wall,
  • wounds to internal structures such as the esophagus or trachea (windpipe), especially following ingestion or inhalation of a foreign objects,
  • a migrating foreign body such as a grass seed that entered the body elsewhere, or
  • spread of an infection from the lungs.

What are the clinical signs of pyothorax?

Rapid shallow, open-mouth breathing that may be painful, depression, lethargy, decreased appetite, and other signs of general illness are seen in most dogs with pyothorax. These dogs usually have a high temperature that contributes to some of the clinical signs. Rapid, open-mouth breathing or breathlessness is caused by the presence of fluid in the chest that prevents the lungs from expanding normally. The severity of these signs is extremely variable, and dogs may suddenly die without having had any previous signs of illness.

How is pyothorax diagnosed?

Clinical examination by a veterinarian may provide some indication of fluid within the chest particularly on listening to the chest with a stethoscope.

In mildly affected cases, chest radiographs (X-rays) will be performed to determine the presence and location of fluid in the chest. In severe cases, it may be necessary to drain the fluid off of the chest immediately (a procedure called a thoracocentesis or chest tap) before taking X-rays. Sedating the dog may be required to allow drainage of the chest.

In many cases, the pus from both sides of the chest can be drained from one side, although it may be necessary to drain both sides in some dogs. Sometimes, the fluid is present in pockets and multiple drainage procedures must be performed. Your veterinarian will send samples of the fluid to a laboratory for evaluation and bacterial culture and sensitivity testing so that the correct antibiotic can be administered.

How is pyothorax treated?

Drainage of the infected fluid plays an important part in the treatment of this condition.

Drainage may be needed on multiple occasions during the initial treatment period. In most cases, a flexible catheter will be inserted into the chest to remove the fluid. The chest cavity may also be flushed with fluids (lavage) via the tube.

"Drainage may be needed on multiple occasions during the initial treatment period."

In some cases, a chest drain may be inserted surgically, allowing drainage of the chest and administration of antibiotics into the chest cavity. The drain may be left in place for several days to allow these procedures to be repeated.

Treatment with oral antibiotics is essential. These may be prescribed for several weeks. In very sick dogs, supportive treatment with intravenous fluids may also be needed in the initial stages.

What is the long-term outlook for a dog with pyothorax?

This depends on the cause of the disease. In those cases where no underlying disease is found, the outlook is good, if the dog survives the critical initial stages. Unfortunately, a proportion of dogs will die in the early stages of their disease.

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