Pulmonary embolism

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Pulmonary embolism

Respiratory system


Pulmonary embolism


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USMLE® Step 1 questions

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High Yield Notes

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Pulmonary embolism

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USMLE® Step 1 style questions USMLE

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A 55-year-old woman comes to the emergency department because of new onset shortness of breath and chest pain for the past 3 hours. She reports that she was walking to her car when the symptoms started, and she describes the pain as sharp and worse with deep inhalation. Additionally, she says she has been coughing up bloody mucus for the past hour. Her medical history is significant for breast cancer, for which she is currently undergoing radiation therapy. Her temperature is 37.5°C (99.5°F), pulse is 110/min, respirations are 24/min, blood pressure is 140/80 mm Hg, and oxygen saturation is 89% on room air. Troponin is 0.08 ng/mL and brain natriuretic peptide (BNP) is 425 pg/mL. Which of the following is the best investigation for diagnosing this patient’s condition?  

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Chest pain

pulmonary embolism p. 697

Electrocardiogram (ECG)

with pulmonary embolism p. 697


pulmonary emboli p. 697

Pulmonary embolism p. 697

chronic thromboembolism p. 703

deep venous thrombosis and p. 697

direct factor Xa inhibitors for p. 443

heparin for p. 443

respiratory alkalosis p. 616

tamoxifen/raloxifene and p. 449

thrombolytics for p. 445

ventilation/perfusion with p. 691

Respiratory alkalosis p. 616

pulmonary embolism p. 697

Sudden death

pulmonary embolism p. 697


pulmonary embolism p. 697


pulmonary embolism p. 697


A pulmonary embolism happens when an embolus, which is a type of blockage, suddenly gets lodged inside a pulmonary artery.

Depending on which pulmonary artery or arteries are affected by the blockage, that can seriously decrease the amount of oxygenated blood that gets out to the body.

Normally, blood makes it back to the heart from all of the tissues and organs through a network of veins that merge over and over.

Superficial veins drain blood into deep veins, which rely on the skeletal muscle pump to move blood forward. The way it works is that the surrounding skeletal muscles compress the vein and propel blood forward, and the veins prevent blood from moving backwards by using one-way valves.

Ultimately, all of the blood ends up in the superior or inferior vena cava and dumps into the right atrium.

From there the blood goes into the right ventricle and gets pumped into pulmonary artery and eventually into the lungs.

The pulmonary artery splits at a spot called the pulmonary saddle, which looks like a bit like a horse saddle, and then the right and left pulmonary arteries enter their respective lungs.

Subsequent branches off the pulmonary artery lead to smaller and smaller arteries, then arterioles, and finally capillaries that form nets around the alveoli, which is where gas exchange occurs.


Pulmonary embolism (PE) is a blockage of the lungs main artery or one of its branches by a substance that has traveled from elsewhere in the body through the bloodstream (embolism). PE most commonly results from a deep vein thrombosis (commonly a blood clot in a leg) that breaks off and migrates to the lung, a process termed venous thromboembolism (VTE). This can cause serious damage to the lung tissue and can be life-threatening.

Symptoms vary by the amount of downstream lung tissue denied blood, which creates a ventilation-perfusion mismatch. They include shortness of breath, chest pain, and coughing. PE can also cause low blood oxygen levels, which can lead to confusion, loss of consciousness, and even death. Treatment of PE typically involves supportive therapy and blood thinning medications to dissolve the clot and prevent further clots from forming. Sometimes a filter is placed in the vena cava to trap clots before they reach the lungs.


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  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Thrombosis" Arteriosclerosis, Thrombosis, and Vascular Biology (2014)
  6. "Acute pulmonary embolism: An update on diagnosis and management" Current Problems in Cardiology (2005)
  7. "Epidemiology, Pathophysiology, and Natural History of Pulmonary Embolism" Seminars in Interventional Radiology (2018)

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