What is a pulmonary thromboembolism?
Pulmonary means lung, and thromboembolism describes an obstruction of a blood vessel by a blood clot that has dislodged from another site.
A pulmonary thromboembolism (PTE) 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.
PTE seems to be more common in medium to large-breed dogs, and generally in middle-aged to older dogs.
What are the typical signs of pulmonary thromboembolism?
The typical signs of pulmonary thromboembolism include:
- sudden difficulty breathing
- rapid breathing
- decreased appetite (anorexia)
- fainting/collapse
- coughing
- spitting up blood
- weakness
- exercise intolerance
- inability to get comfortable
How is pulmonary thromboembolism diagnosed?
Your veterinarian may find several important clues during a physical examination that point to a pulmonary thromboembolism. Your dog may have a rapid heart rate with weak pulses, and he may have a heart murmur. His gums may be pale or even bluish from low oxygen levels 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 refill with blood. An oxygen sensor placed on the gums or skin will often read too low.
"Chest X-rays are often normal, but may show abnormalities such as fluid in or around the lungs or enlargement of pulmonary blood vessels."
Blood testing can reveal clues about why your dog is forming blood clots. Chest X-rays are often normal, but may show abnormalities such as fluid in or around the lungs or enlargement of pulmonary blood vessels. Other testing may be recommended, including echocardiography (ultrasound of the heart) and blood clotting profiles. Definitive diagnosis can be made with a CT scan using contrast dye (angiography) to show the blood vessels.
What could have caused my dog to have a pulmonary thromboembolism?
There are many important considerations and potential causes of PTE in dogs:
- canine heartworm disease
- cancer
- Cushing’s disease (excessive levels of steroids produced by the adrenal glands)
- steroid medication administration
- protein losing nephropathy (kidney disease in which protein is lost into the urine)
- protein losing enteropathy (intestinal disease in which protein leaks into the intestines and is lost into the stool)
- immune-mediated hemolytic anemia (IMHA), in which the dog’s immune system destroys its own red blood cells
- pancreatitis
- heart disease
- bone surgery or trauma
- bacterial infection in the bloodstream (sepsis)
- liver disease
- clotting of the blood within the blood vessels, called disseminated intravascular coagulopathy (DIC)
How is pulmonary thromboembolism in dogs treated?
Many dogs with thromboembolism are first treated as inpatients until the oxygen levels in their blood return to normal. Oxygen therapy may be a part of their treatment, but response to oxygen therapy is variable. Once the dog returns home, it is important to restrict activity to prevent fainting and further decline in blood oxygen levels.
Some medications are available for treating this disorder. Heparin is a medication to prevent blood from clotting (anticoagulant). It may help to prevent future clots but will not break up existing clots. Warfarin is another anticoagulant that may be considered for long-term treatment. With warfarin, dosage adjustments are necessary to keep blood clotting at a specific level, and to balance the risk of further clots with the risk of bleeding complications.
Anti-platelet medications such as clopidogrel (e.g., brand name Plavix®) or Aspirin are also sometimes used as preventive medications in dogs with disorders that might put them at increased risk of developing PTE.
Medications to dissolve existing clots (thrombolytic drugs) have been tried but their effective use without complications is not clear.
What kinds of monitoring and follow-up will my dog need?
Monitoring oxygen levels in the blood through pulse oximetry (a non-invasive sensor used on the outside of the body) allows for tracking of improvement in breathing function. Your dog will need blood tests to check blood clotting status, which is required to adjust 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 the development of future blood clots.
What is the outlook for my dog?
The prognosis for dogs with pulmonary thromboembolism is generally guarded to poor, and it depends on resolution of the underlying cause. Dogs tend to have a better prognosis when the cause of their pulmonary thromboembolism is trauma or generalized bacterial infection.
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 may lead to bleeding complications, necessitating frequent re-evaluation of clotting times, and these medications may be required long-term.
