Pulmonary thromboembolism is the sudden occlusion of a lung artery
It is due to a blood clot that dislodged somewhere else in the body
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In most cases, pulmonary thromboemboli primarily originate from a deep vein thrombosis of the leg
Treatment is anti-coagulation and/or thrombolytic therapy
What is pulmonary thromboembolism?
Pulmonary thromboembolism is the sudden occlusion of a lung artery due to a blood clot that dislodged somewhere else in the body. This leads to obstruction of the blood supply to the lung tissue and severe chest pain and shortness of breath. If not treated aggressively, it can lead to respiratory and circulatory collapse and death.
What causes pulmonary thromboembolism?
The causes of pulmonary thromboembolism are basically the causes of thrombosis. The cases can be divided into three categories:
Damage to the venous endothelium (lining of the vein) due to indwelling catheters, injection of irritating substances into the vein, sepsis, etc)
Venous stasis (postoperative, after child birth, varicose veins, etc)
More than 90% of pulmonary thromboemboli primarily originate from a deep vein thrombosis (DVT) of the leg. In theory, any blood clot that originates in any vein other than the lung veins can dislodge and cause pulmonary embolism.
Less than 20% OF DVT’s will propagate into the iliofemoral veins of the upper leg. It is usually here where pieces of thrombus (blood clot) break off and move through the heart into the lungs. The incidence of this ranges from 30 to 50%.
Who gets pulmonary thromboembolism and who is at risk?
The risk factors for developing thrombosis include the following:
Elderly people
Fractures of the femur, hip and pelvis
Heart failure and heart attack patients
Obesity
Post operative patients
Pregnancy and just after childbirth
Prolonged immobilization/inactivity (eg, “tourist class syndrome”, bedridden patients, etc)
Symptoms and signs of pulmonary thromboembolism
The symptoms associated with pulmonary thromboembolism can vary from asymptomatic to sudden death. There is no single symptom or sign that will indicate pulmonary thromboembolism with 100% accuracy. The symptoms and signs also vary according to the presence of underlying heart and lung pathology, the size of the embolus and the area of the embolism. The symptoms and signs start abruptly (within 5 minutes) and may be intense. The intensity will decrease over days as the clot starts dissolving and the lung starts repairing itself.
The symptoms of pulmonary thromboembolism include:
Chest pain
Shortness of breath
Anxiety and restlessness
Cough
Coughing up blood
Excessive sweating
Dizziness and loss of consciousness
The signs of pulmonary thromboembolism include:
Cyanosis
Decreased blood pressure
Difficulty in breathing
Increased breath rate
Increased second heart sound
Increased/racing pulse
Irregular pulse rate
Low grade fever
How is pulmonary thromboembolism diagnosed?
The diagnosis of pulmonary thromboembolism is usually suspected clinically on the history and the symptoms and signs. Special tests are then used to confirm the diagnosis.
Routine laboratory tests are seldom helpful in confirming the test of pulmonary thromboembolism. They will show that the patient is hyperventilating or that they’re cyanotic, but this doesn’t prove that the person has a pulmonary thromboembolism.
Although pulmonary thromboembolism causes typical changes on an ECG, these changes are not specific enough to confirm the diagnosis. Serial ECG’s are helpful in excluding other disorders that may mimic the symptoms and signs of pulmonary thromboembolism (e.g. myocardial infarction).
Chest X-rays are often normal, but may show typical signs in the case of a massive pulmonary thromboembolism.
When pulmonary thromboembolism is suspected it is traditionally investigated with a Ventilation/Perfusion Scan. This will show if there is disturbance in regional blood flow which can be compared to the areas of the lung which are ventilated. A pulmonary embolism will typically show a mismatched defect (i.e. an area which is ventilated but not perfused). Other lung conditions can cause disturbance of ventilation perfusion/relationships, but with significant mismatched defects and in the right clinical setting, this investigation can be very accurate. Because of the difficulties interpreting these scans the tendency today is to investigate with spiral CT, which will demonstrate a clot in the pulmonary artery and has the advantage of showing the lung fields very clearly and demonstrating other lung pathology. With this technique pulmonary angiography is rarely needed.
Pulmonary angiography is a very sensitive and specific test for pulmonary thromboembolism and can pick up a pulmonary thromboembolism as small as 3mm in diameter. It shows the lung arteries just like an angiography of the coronary arteries does in the case of a myocardial infarction. It is an expensive and sometimes dangerous test and is thus not done as routinely as one would think. If there is any doubt about the diagnosis, pulmonary angiography will be the definitive answer.
Can pulmonary thromboembolism be prevented?
The most important area where DVT and pulmonary thromboembolism can be prevented is postoperatively. Patients are mobilized as early as possible after major operations and heparin is given to make the blood less likely to clot.
Other steps one can take are to keep one’s weight healthy, not smoke and to get up for a walk every hour or so on long flights.
How is pulmonary thromboembolism treated?
The treatment of pulmonary thromboembolism depends on the severity.
In massive pulmonary embolism thrombolytic therapy to dissolve the clot is indicated, but has attendant risks.
Very occasionally the clot may need to be removed surgically.
The majority of patients are treated with heparin, which may be given intravenously as a constant infusion or as low molecular weight heparin, given as a subcutaneous injection once or twice a day.
The effects of the pulmonary embolism, such as low blood pressure and arterial oxygen levels, are treated appropriately and pain is relieved.
Warfarin, an oral anticoagulant, is commenced at the same time as heparin.
What is the outcome of pulmonary thromboembolism?
Although pulmonary thromboembolism may cause sudden death, the outcome is generally good. If the diagnosis is made early in the disease and the appropriate treatment is given, the mortality rate is decreased tenfold from about 30% to 3%. If a patient survives the acute episode, he should recover completely with no lasting after effects. He will need to continue to use warfarin for three to six months if there is an identifiable cause for the clot and lifelong if there is no obvious reason for the clot.
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