Pulmonary Embolism. A blood clot in the lungs may kill you before you know it.

Pulmonary Embolism. A blood clot in the lungs may kill you before you know it.

A third of people with pulmonary embolism die before they reach the hospital. In other words, a blood clot in the lungs kills them before they become aware of its existence. Anything that either slows your blood: thickens it, or damages blood vessels is a risk factor. Diagnosis is challenging because no single symptom is specific to the presence of such clots in the lungs. Treatment involves blood thinning with advanced care like clot breakdown and filters in selected patients.

The word ‘pulmonary’ describes anything relating to the lungs. A blood clot that forms within a vein is a thrombus. When it dislodges (migrates) to a distant site, it becomes an embolus. So, we define pulmonary embolism as a medical emergency that ensues when a blood clot (embolus) blocks the blood vessels within the lungs (pulmonary artery or its branches). The blood clot (thrombus) often dislodges from one of the veins in the lower limbs and settles in the lungs. It rarely does so from the upper limbs.

Pulmonary Embolism. A blood clot in the lungs may kill you before you know it.
The circulatory system of heart and lungs, computer artwork, showing a thrombus in the right lung. This occurs when one of the pulmonary arteries is blocked, usually by an abnormal blood clot, that has broken off the wall of a vein in the leg or pelvis after forming deep vein thrombosis. The two branches of the pulmonary artery (red) carry deoxygenated blood from the heart to the lungs. Oxygenated blood returns from the lungs in the two branches of the pulmonary vein (blue-violet).

Blood clots comprise platelets, red blood cells, and fibrin. Three scenarios offset the formation of blood clots – when blood flow becomes sluggish (stasis): it is thick (hypercoagulability) or vessel walls are damaged (endothelial injury).

Several factors can cause any of the above three scenarios to happen – risk factors. You can inherit or acquire them.

Inherited factors include disorders of blood clotting and sickle cell disease.

Acquired factors include age above 60 years, cancer, hormone replacement therapy and oral contraceptives: heart failure, indwelling venous catheters, immobilisation (bed rest >3hours; car rides, and air travel), infections (like Covid-19), pregnancy, heavy smoking, stroke, history of blood clots, obesity, trauma, surgery, and certain drugs like tamoxifen, bevacizumab, et cetera.

Pulmonary Embolism. A blood clot in the lungs may kill you before you know it.
Medical doodles of DVT(Deep Vein Thrombosis)/PE(Pulmonary Embolism) Health Conditions. Medical Icon Set. Vector. Isolated on background.

When a clot dislodges into the lung vasculature, it cuts off the blood supply to the distant lung tissue. No blood supply may cause lung infarction (ischaemia) or deprive the body of enough oxygen. Also, because of the blockage, the right side of the heart becomes strained by the returning blood from the rest of the body that it can no longer pump to the lungs via the pulmonary artery for oxygenation. The result is acute right-sided heart failure which may suddenly kill you.

In a few scenarios, the clots are small but pile up within the lung vessels (pulmonary arteries), the vessel walls thicken to cause pulmonary hypertension. Untreated pulmonary hypertension stretches the right side of the heart, causing right-sided heart failure.

Mostly, small emboli within the pulmonary arteries show no symptoms. However, acute, massive pulmonary embolism may present with sudden shortness of breath, chest pain, increased heart rate (tachycardia), fast breathing (tachypnoea), coughing up blood (haemoptysis), and death.

On rare occasions, you may have noisy breathing (wheezing): nausea, sweating, and a cold clumsy skin appearance.


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A diagnosis of pulmonary embolism requires a high degree of suspicion. It should be swift, or you may die before the clinicians figure it out. Fortunately, the chances of death are lower upon arrival at the hospital than in the community. We estimate that up to a third of people with pulmonary embolism die before they become aware of it.

After history taking and physical examination, a clinician may request a series of tests to delineate a pulmonary embolism diagnosis. They may include d-dimers, electrocardiography, and echocardiography: chest x-ray, chest CT scan (CT- pulmonary angiography), cardiac enzymes, ventilation/perfusion scans, duplex ultrasound scan of the lower limbs, clotting profile, among others. The chronology of these and other tests depend on how you present.

Upon a diagnosis, the clinicians may admit you for stabilisation and treatment. The clinicians may give you supplemental oxygen and medications to dissolve the clot.

We call them blood thinners (anti-coagulants). They include heparin, warfarin, rivaroxaban, among others.

Treatment may continue for up to six months or more. A few patients may require aggressive clot dissolution.

Such patients may have a catheter placed into the pulmonary artery to break down the clot. Others may need a filter (Greenfield) on one of the veins draining blood into the heart from the legs (inferior vena cava) to prevent recurrent embolism.

Because blood clot formation is an entirely preventable phenomenon, it is imperative that you identify all the risk factors and modify them. Do not smoke. Wear loose clothes that enhance blood flow. Avoid prolonged bed rest or sitting. For long travels, occasionally move your legs and bend your ankles and toes. You may need compression stockings after trauma or major surgery.

Contact a clinician if you develop pain in the lower limbs: they swell or experience uncontrolled bleeding. While on blood thinners, stay in touch with your doctor to ensure prompt monitoring.

In summary, several factors can lead to blood clot formation within the deep veins. The clots may dislodge into the lungs and cause a pulmonary embolism. It is incumbent upon us to identify those at risk and take them to the hospital for further evaluation. Pulmonary embolism can cause sudden death, but when promptly diagnosed, mortality is minimal. It is paramount to ascertain that anything that injures your blood vessel walls: thickens your blood, and slows down circulation is a risk factor for clot formation.

For more information, the following sites will be helpful.

UpToDate: MSD manuals.

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