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Pulmonary Thromboembolism (Blood Clots in the Lungs) in Cats


Emergency Situations, Medical Conditions, Pet Services

My cat suddenly had trouble catching her breath and then she fainted. At the pet emergency room, they diagnosed a blood clot in her lung. They called it a pulmonary thromboembolism. The explanation was very complex and I am not sure I understand the details.

pulmonary_thromboembolismPulmonary means lung, and the word thromboembolism describes a blood clot that has moved through the blood vessels, lodged in one of the pulmonary arteries, and blocked blood flow into the portion of the lung served by that artery. This seems to be more common in medium to large-breed cats, and generally in middle-aged to older cats.

What are the typical signs of pulmonary thromboembolism?

The signs of pulmonary thromboembolism include:

  • very sudden difficulty breathing
  • rapid breathing
  • decreased appetite or anorexia
  • fainting
  • coughing
  • spitting up blood
  • weakness
  • exercise intolerance
  • inability to get comfortable

Your veterinarian may find several important clues about pulmonary thromboembolism during a physical examination. Your cat may have a very rapid heart rate with weak pulses, and she may have a heart murmur. Her gums may be pale or even bluish from a too low oxygen level in the blood. When your veterinarian presses on the gums to push away the blood, it takes longer than normal for the small blood vessels to re-fill with blood.

What could have caused my cat to have a pulmonary thromboembolism?

There are many important considerations and potential causes of pulmonary thromboembolism in the cat. Feline heartworm disease is one potential cause, emphasizing the need to provide appropriate monthly protection against heartworm disease with preventative medication. Other important potential causes of feline thromboembolism include cancer, excessive levels of steroids produced by the adrenal glands during Cushing’s disease, steroid medications, and kidney disease in which protein is lost into the urine.


Other potential causes of pulmonary thromboembolism include:

  • immune-mediated hemolytic anemia (IMHA), in which the cat’s immune system destroys the cat’s own red blood cells
  • pancreatitis
  • heart disease
  • bone surgery or trauma
  • bacterial infection in the bloodstream
  • liver disease
  • clotting of the blood within the blood vessels, called 'disseminated intravascular coagulopathy' (DIC)

How is pulmonary thromboembolism in cats treated?

Many cats with thromboembolism are first treated as inpatients until the oxygen levels in their blood returns to normal. Oxygen therapy may be a part of their treatment, but response to oxygen therapy may be variable.

Once the cat is returned home, it is important to restrict activity in order to prevent fainting, and the low oxygen levels in the blood from declining further. There are very few medications available for treating this disorder. Heparin is a medication to prevent blood from clotting (anticoagulant) that may help to prevent future clots from forming, but will not cause existing clots to break up. Warfarin is another anticoagulant that may be considered for long-term treatment. With it, dosage adjustments are necessary to keep blood clotting at a specific level, and carefully balancing the risk of further clots with the risk of bleeding complications is needed to prevent development of further clots.


What kinds of monitoring and follow-up will my cat need?

Monitoring oxygen levels in the blood through pulse oximetry allows for tracking of improvement in breathing function. Blood tests to check blood clotting status will be needed for adjusting the dose of warfarin. Bleeding complications may arise in pets treated with anticoagulant medications.

Controlled activity or physical therapy may improve general blood flow and prevent development of future blood clots.

What is the outlook for my cat?

The prognosis for cats with pulmonary thromboembolism is generally guarded to poor, and it depends upon resolution of the underlying cause. Cats for whom the cause of their pulmonary thromboembolism is trauma or generalized bacterial infection tend to have a better prognosis.

Future episodes of pulmonary thromboembolism are likely unless an underlying cause is identified and corrected. These blood clots are often fatal, and sudden death is not unusual. Treatment with anticoagulant medications can lead to bleeding complications, necessitating frequent reevaluation of clotting times, and these medications may be required long-term.

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