Pulmonary embolism
How a clot from a deep leg vein lodges in the pulmonary arteries, why it creates dead space and hypoxaemia, how a large embolus strains and can fail the right ventricle, and why lung infarction is uncommon.
By the end, you can
- Describe the low-pressure pulmonary circulation and the right ventricle’s limited tolerance of a sudden load.
- Explain how Virchow’s triad leads to a deep vein thrombosis and how a fragment reaches the lungs.
- Relate dead space and V/Q mismatch to hypoxaemia with a low PaCO2.
- Explain how a large embolus causes right ventricular dilatation, septal shift and shock.
- Explain why pulmonary infarction is uncommon and what can happen after the acute event.
- Recognise the classic appearances, scores and tests of PE, and explain how anticoagulants, thrombolysis and other treatments act on its mechanism.
What it is
Pulmonary embolism (PE) is blockage of one or more pulmonary arteries by material carried in the blood, nearly always a thrombus from the deep veins of the legs or pelvis. Together with deep vein thrombosis it forms venous thromboembolism (VTE).
3 types to tell apart
- High-risk (massive) PE
- Causes sustained low blood pressure or shock because the right ventricle fails.
- Intermediate-risk (submassive) PE
- Blood pressure is maintained, but the right ventricle is dilated or strained on imaging or blood tests.
- Low-risk PE
- No right ventricular strain and normal blood pressure; often smaller or more distal emboli.
Normal function
The pulmonary circulation: low pressure, high capacity
The pumps the whole cardiac output through the and the and , whose branches follow the airways to every alveolus. It is a low-pressure, low-resistance circuit: mean pulmonary artery pressure at rest is about 15 mm Hg, against about 90 mm Hg in the aorta.
The thin-walled right ventricle suits this light load. When flow rises, closed capillaries open (recruitment) and open ones widen (distension), so pressure barely rises. But the right ventricle copes poorly with a sudden rise in resistance.
Ventilation and perfusion are matched so that each alveolus receives blood in proportion to its air. The lung also has a second supply, the bronchial arteries from the aorta, which nourish the airways and supporting tissue.
Underlying change · Step 1 of 4
A deep vein thrombus breaks free
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 2 of 4
Ventilated but not perfused: dead space and hypoxaemia
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 4
Right ventricular strain
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 4 of 4
Where emboli lodge, infarction and what follows
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .