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Hemothorax: Bleeding in the Chest in Dogs

By: Dr. Douglas Brum

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A hemothorax is a potentially life threatening situation. In a normal animal the space between the lungs and the inner chest wall is called the pleural space. This space is more of a potential space, since a vacuum is present and the lungs are always in close contact with the pleural (inner lining) surface of the chest. Thus, as the chest or diaphragm expand, the lungs expand passively as well. If the pleural space becomes filled with blood, there is less room for the lungs to expand and fill with air. Breathing becomes more labored, and less oxygenated blood is distributed to the body. As the volume of blood increases, the ability to breath decreases and rapid intervention is needed.

Rapid blood loss into the chest can also lead to a decrease in blood pressure and tissue perfusion. This may lead to shock. As continued blood is lost, a decrease in circulating red blood cells may lead to acute (sudden) anemia. If veterinary care is not immediately available, rapid blood loss may lead to death. A slower blood loss is more common and will allow for more time to seek veterinary care.

Chronic (long standing) or intermittent blood loss generally occurs more slowly, and more subtle clinical signs might be present. If the blood loss is slow, the body can reabsorb the free blood in the chest. Thus, animals may only have a small amount of blood present in the chest cavity. These animals may not present as an emergency with breathing problems, but they still may have a serious underling disease process. Making the diagnosis of a hemothorax is critical in establishing an underling cause.

If the animal has normal clotting parameters the bleeding into the chest will, many times, stop on it's own. Blood clots form that stop the bleeding. Blood clots can, however, be dislodged especially with increased movement or manipulations. If blood clots are dislodged, the bleeding may start again. In many cases of hemothorax due to chest trauma, the bleeding will stop on it's own.


There are several main causes of a hemothorax. Trauma is the most common cause. A lacerated blood vessel within the thorax or pleural lining may lead to rapid or slow bleeding depending on the amount of trauma and the size of the affected vessel or vessels. Outdoor animals are at significantly greater risk then indoor animals. Younger animals are more likely to be injured as well. In young animals with a hemothorax and no history of trauma, a coagulopathy (bleeding disorder) should be suspected. Bleeding into the chest usually does not stop on it's own, 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 cause. Bleeding tumors may cause a rapid blood loss or be chronic, having intermittent smaller bleeding events. Specific causes of hemothorax include:

  • Trauma. The most common traumatic injury causing a hemothorax occurs when a car has hit an animal. Severe chest trauma may cause a very rapid death if the bleeding is significant. Sometimes the bleeding occurs more slowly and there is time to seek emergency care. Fractured ribs may lacerate vessels leading to bleeding into the thorax (chest). Other cause of trauma include gun and knife wounds.

  • Tumors. Tumors in the thorax may erode a blood vessel or rupture and cause an acute bleed. Tumors located on the pleural surface of the chest, blood vessels within the chest, lungs or heart may all cause a hemothorax. The most common tumor to cause a bleed is hemangiosarcoma (a malignant tumor of blood vessels). These tumors are commonly found on the right atrium of the heart. Golden retrievers and German shepherd dogs are two breeds at increased risk of getting this tumor.

  • Coagulopathies. Rodenticide poisoning with products containing anticoagulants is a very common cause of bleeding disorders in animals. The bleeding may be exclusively in the chest, or may more commonly 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.

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