What is pulmonary embolism?

Pulmonary embolism (PE) occurs when a blood clot- also known as a thrombus- gets lodged in one of your pulmonary arteries (arteries supplying the lungs) which blocks the blood flow to your lungs.  These blood clots originate mainly from the deep veins in your legs and travel all the way up to your lungs through your heart.  A thrombus is a blood clot formed in your veins.  An emboli is when a thrombus dislodges from its original location to get stuck in another blood vessel.

The incidence of PE in the United States is 1 case per 1000 persons per year.  In addition, PE is the 3^rd most common cause of death in hospitalised people.  Unfortunately, a study showed that in 60% of people who have died in a hospital setting, 70% of them died due to PE, in which the diagnosis was missed.  The main cause of PE is Deep Venous Thrombosis (DVT)- this is when blood clots  form inside the deep veins located in your legs- as PE is present in 60-70% of people with DVT.  This condition is more common in men than women.  Furthermore, it is more common in blacks than whites.

This condition is common and potentially fatal.  However, with the appropriate treatment in a timely manner, death can be prevented.

What are the causes and risk factors of pulmonary embolism?

There are mainly 3 factors which predispose someone to the formation of blood clots within the veins and triad is known as the Virchow’s triad:

• Endothelial injury: This is when the inner walls of your veins get damaged or injured.  It may be injured due to smoking, hypertension or physical inactivity.
• Venous stasis or turbulence of blood flow: When the flow of blood within your veins is too slow or inexistent, there is accumulation of platelets and thrombin- these are important substances which make blood clot formation possible- which increases your risk of developing a thrombus.
• Blood hypercoagulability: Prolonged venous stasis or mutation of the factor V Leiden makes your blood thicker which increases your risk of developing a thrombus.  Deficiency in the proteins C & S and antithrombin III are other risk factors for DVT and PE.  Factor V Leiden, protein C & S and antithrombin III play a role in the formation of blood clots and are known as clotting factors.

Other causes of pulmonary embolism include:

• Immobilization: Immobilization leads to the accumulation of clotting factors which increases your risk of developing a blood clot within your veins.
• Surgery and trauma: Surgery and major trauma activate your clotting factors to stop bleeding and cause immobility.  As a result, the chance of blood clot formation within your veins is high.  As a preventive measure, people immobilised for long periods of time in hospitals are prescribed blood thinners which significantly reduces the risk of thrombus formation.

• Pregnancy: The incidence of PE in pregnant women is as high as 1 case in every 200 deliveries.  However, fatal events are rare.
• Oral contraceptives and hormones replacement therapy: Using these medications increases your risk of developing PE by 3 times.
• Cancer: There are certain cancers which are associated with PE and these include pancreatic, lung, colon, stomach and breast cancer.
• Hereditary factors: There are many factors which you may inherit from your parents which increases your risk of developing a thrombus and these include antithrombin deficiency, protein C & S deficiency, factor V Leiden deficiency, plasminogen and fibrinogen abnormality.
• Acute medical illness: There are several acute medical illnesses which are associated with PE and these include congestive heart failure, Human Immunodeficiency Virus (HIV)/Acquired Immunodeficiency Syndrome (AIDS), Systemic Lupus Erythematosus (SLE) and ulcerative colitis.
• Other risk factors: other risk factors for PE include intravenous drug abuse, inflammatory bowel disease, smoking, prior PE, stroke, varicose veins, airplane travelling, hyperlipidaemia and haemolytic anaemia amongst others.

What are the signs and symptoms of pulmonary embolism?

The symptoms of PE are very often not classic, that is sudden onset of chest pain, shortness of breath and coughing.  Atypical symptoms include:

• Seizures
• Loss of consciousness
• Fever
• Abdominal pain
• Coughing up of blood

• Wheezing- this is a high-pitched whistling sound produced when you breathe.

Physical signs of PE include:

• Increased respiratory rate
• Increased heart rate
• Fever
• Increased heart sound
• Sweating
• Swelling of the legs and feet
• Cyanosis- the bluish coloration of the skin and mucous membranes due to lack of oxygen in your blood.
• Hypotension- in severe cases, the blood pressure may fall below 90/60 mmHg.
• Altered mental status

Making a diagnosis

To make a diagnosis, your doctor will first take a detailed history from you to know more about your symptoms.  After the history taking, your doctor will perform a thorough physical examination to look for signs of PE.  He/she may order some tests to confirm the diagnosis and these include:

• D-Dimer test: D-Dimer is a small protein made from the degradation of blood clots.  A negative result indicates a low likelihood of PE and is used to exclude the diagnosis of PE.  This test should be used in cases where the doctor is not sure about the diagnosis after the history taking and physical examination.
• White Blood Cell (WBC) count: In PE the WBC count is often normal or elevated.
• Arterial Blood Gas (ABG): This test is used to measure the acidity, oxygen and carbon dioxide levels in your blood.  It is mainly indicates whether your lungs are functioning properly.

• Venography: This test is used for the diagnosis of Deep Vein Thrombosis (DVT) which is often associated with PE.
• Pulmonary angiography: This test is a useful diagnostic modality for the diagnosis of PE as a positive result provides 100% certainty that there is an issue with the pulmonary blood flow.
• Computed Tomography (CT) scan: CT scan is the initial imaging of choice in sable people with suspected PE.  This test can demonstrate the emboli directly and is preferred over pulmonary angiography as it is cheaper and non-invasive.
• Chest radiography: Chest radiographs are abnormal in most cases of PE.  However, initially there might be no abnormalities.  In later stages of PE, dilatation of the pulmonary blood vessels may be seen. 
• Ventilation-Perfusion scanning:   This test is also known as V/Q scanning and is an important test to make the diagnosis of PE.  It is used when CT scan is not available, when you are allergic to the contrast material or CT scan is contraindicated.  It shows areas of your lungs not having enough blood supply.
• Electrocardiography (ECG): ECG is used to exclude heart diseases and also to look for a sign of PE seen on the ECG strip which is known as the S1 Q3 T3.
• Magnetic Resonance Imaging (MRI) scan: MRI scan can detect any abnormalities in your pulmonary blood flow and if there is any damage to the lungs.

• Echocardiography: This test assess the function of your heart and help to exclude any heart condition which might be confused with PE.
• Duplex ultrasonography:  This test is used to detect the presence of DVT at any site which help in the diagnosis of PE.  The ultrasonic transducer- the tool receiving the image in 2-D- is placed on the skin to detect veins.  Then, it is pressed inward firmly to compress the vein.  Signs of DVT will be a vein which cannot be compressed completely.

What are the treatments of pulmonary embolism?

There are several treatment options available to treat PE and these include:

• Thrombolysis: These medications work by dissolving blood clots and are mainly used in people with acute PE with hypotension.
• Anticoagulation: These medications work by preventing the formation of blood clots.  Examples include fondaparinux, dabigatran and heparin amongst others.  They are also known as blood thinners.
• Embolectomy: Catheter or surgical Embolectomy is the removal of the emboli.  It is especially useful in people with massive pulmonary embolism who cannot undergo thrombolysis.
• Vena cava filters: This is particularly useful in people who cannot undergo anticoagulation therapy, had recent surgery or haemorrhagic stroke.  This filer is able to trap emboli without causing occlusion of the vena cava which is the largest vein in the body, supplying the heart.

What are the complications of pulmonary embolism?

If PE is left untreated, the following complications may ensue:

• Sudden cardiac death
• Cor pulmonale
• Lung infarction
• Pleural effusion
• Arrhythmias
• Shock
• Thrombophlebitis

Prognosis

The prognosis of pulmonary embolism mainly depends on the severity of the disease and the appropriate diagnosis and treatment, in a timely manner.  10%of people with PE die within the first hour.  Suffering from DVT significantly increases your risk of developing PE.

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Ouellette, D., 2020. Pulmonary Embolism (PE).