Hemothorax: Bleeding in the Chest in Cats

The space between the lungs and inner chest wall is called the pleural space. In health, this space is a potential space, with negative pressure holding the lungs in contact with the inner chest wall. As the chest expands, the lungs expand as well, and air flows in.

If the pleural space fills with blood, there is less room for the lungs to expand and fill with air. Breathing becomes labored, gas exchange is impaired, and less-well oxygenated blood is distributed to the body. As the volume of blood in the chest cavity increases, the ability of the cat to breathe properly decreases and rapid intervention is needed.

Rapid blood loss into the chest leads to a decrease in blood pressure and tissue perfusion. A state of hemorrhagic shock ensues. As blood loss continues, there is a fall in numbers of circulating red blood cells, causing anemia.

If veterinary attention is not found quickly, rapid blood loss or respiratory failure may lead to the cat's death. Situations in which blood is lost more slowly allows for more time for veterinary care to be sought.

Chronic (long standing) or intermittent blood loss creates a slowly insidious condition associated with more subtle clinical signs. When blood loss into the chest is slow, the body can reabsorb some of the blood. Thus, cats with chronic hemothorax may have only a small amount of blood present in the chest cavity. These cats may not present in an emergency situation, in shock and with breathing problems, but may nevertheless still have a serious underlying disease process. Recognizing the existence of hemothorax is critical in establishing an underlying cause and instituting the correct symptomatic treatment.

If a cat with hemothorax has normal clotting parameters, the bleeding into the chest will, often times, stop on its own. Blood clots stop the bleeding. Blood clots can, however, become dislodged, especially in the presence of increased movement or manipulations. If blood clots are dislodged, the bleeding may start again. In many cases of hemothorax caused by chest trauma, the bleeding will stop on its own.

Causes

There are several main causes of a hemothorax - with trauma the leading factor. A lacerated blood vessel within the thorax or pleural lining may lead to rapid or slow bleeding, depending on the extent of the trauma and size of the affected vessel or vessels. Outdoor cats are at a significantly greater risk of acquiring hemothorax than indoor cats. In addition, young cats are more prone to injures that could lead to hemothorax. In young cats with a hemothorax and no history of trauma, a bleeding disorder (coagulopathy) should be suspected. Bleeding into the chest as a result of coagulopathy usually does not stop unless vitamin K or other appropriate therapy is administered. In older animals with a hemothorax and no history of trauma, a bleeding tumor within the chest cavity is often the reason for the condition. Bleeding tumors may cause a rapid or chronic/intermittent blood loss.

Specific causes of hemothorax include:

Trauma. The most common traumatic injury causing hemothorax occurs when a cat is hit an automobile. Severe chest trauma may cause death rapidly if there is extensive bleeding. Sometimes bleeding occurs more slowly and there is time to locate an emergency care facility. Fractured ribs may lacerate vessels leading to bleeding into the thorax (chest). Other causes of trauma include gunshot and knife wounds.

Tumors. Tumors in the thorax may erode into blood vessels or rupture and cause bleeding. Tumors located on the inner surface of the chest wall, tumors of blood vessels within the chest, lungs, or heart, may rupture causing hemothorax.

Coagulopathies. Rodenticide poisoning with products containing anticoagulants is a common cause of bleeding disorders in dogs, though this is less common in cats. Bleeding may occur exclusively into the chest or may involve other sites (e.g. under the skin). Products containing the following active ingredients may cause a hemothorax: warfarin, fumarin, chlorophacinone, diphacinone, pindone, bromadiolone, or brodaficoum.