U01.16.028 Pulmonary Embolism (PE)

Pulmonary embolism (PE) is a blockage in one of the pulmonary arteries in the lungs, typically caused by blood clots that travel to the lungs from the legs or other parts of the body. This condition is a medical emergency and can be fatal if not treated promptly.

Clinical Features

V˙/Q˙ Mismatch: PE leads to a ventilation-perfusion (V˙/Q˙) mismatch, resulting in hypoxemia and respiratory alkalosis.
Symptoms:
- Sudden-onset dyspnea (shortness of breath)
- Pleuritic chest pain
- Tachypnea (rapid breathing)
- Tachycardia (rapid heart rate)
Severe Cases:
- Large emboli or saddle embolus can cause sudden death due to electromechanical dissociation, also known as pulseless electrical activity.

Diagnostic Imaging

CT Pulmonary Angiography: This is the imaging test of choice for diagnosing PE. It identifies filling defects in the pulmonary arteries.
ECG Findings: In some cases, an ECG may show an S1Q3T3 pattern, which can be associated with PE.

Pathophysiology

Lines of Zahn: These are interdigitating areas of pink (platelets, fibrin) and red (red blood cells) seen in thrombi formed before death. They are useful in distinguishing between pre- and postmortem thrombi.

Types of Emboli

Fat Emboli:
- Associated with long bone fractures and liposuction.
- Classic triad: hypoxemia, neurologic abnormalities, and petechial rash.
Air Emboli:
- Caused by nitrogen bubbles in ascending divers (caisson disease/decompression sickness).
- Also can be iatrogenic, secondary to invasive procedures like central line placement.
- Treatment: Hyperbaric oxygen (O2).
Amniotic Fluid Emboli:
- Typically occurs during labor or postpartum, but can also be due to uterine trauma.
- This can lead to disseminated intravascular coagulation (DIC).
- Rare but has a high mortality rate.

Table: Types of Emboli and Associated Features

Type of Embolus	Associated Features
Fat Emboli	Long bone fractures, liposuction; hypoxemia, neurologic abnormalities, petechial rash
Air Emboli	Decompression sickness, central line placement; treat with hyperbaric O2
Amniotic Fluid Emboli	Occurs during labor/postpartum or due to uterine trauma; can lead to DIC, high mortality rate

Table: Types of Emboli and Associated Features

Points to Remember

PE is a life-threatening condition that requires prompt diagnosis and treatment.
CT pulmonary angiography is the preferred imaging method for detecting PE.
Lines of Zahn are indicative of thrombi formed before death.
Different types of emboli, such as fat, air, and amniotic fluid, have distinct clinical features and risks.

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USMLE Step 1 Review Series

Curriculum

U01.16.028 Pulmonary Embolism (PE)

Clinical Features

Diagnostic Imaging

Pathophysiology

Types of Emboli

Table: Types of Emboli and Associated Features

Points to Remember

Bibliography Reference Links

Your voice matters – comment below!Cancel reply

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