Pulmonary edema: hemodynamic vs alveolar-capillary injury
- Lesion
Fluid fills the lung either because pressure in the pulmonary veins is high (heart failure) or because the alveolar wall is damaged and leaks.
What it is
Pulmonary edema is extra fluid in the interstitium and then the alveoli. Hemodynamic (cardiogenic) edema is a protein-poor transudate pushed out by high pressure, most often from left heart failure. Injury (noncardiogenic) edema is a protein-rich exudate from damaged endothelium or epithelium, and in its severe form it is the lesion of ARDS. In both cases the lungs are heavy and wet.
Structure
- Gross: heavy, wet lungs that ooze frothy, sometimes blood-tinged fluid when cut.
- Hemodynamic edema (H&E): engorged alveolar capillaries and pale pink, finely granular transudate filling the alveoli.
- Chronic congestion: many hemosiderin-laden macrophages (golden-brown, Prussian blue positive) and thickened, fibrotic septa.
- Injury edema: protein-rich exudate with inflammatory cells and, when severe, hyaline membranes.
Step by step
- The left ventricle fails, pressure rises in the left atrium and pulmonary veins.
- Capillary hydrostatic pressure exceeds the oncotic pressure that holds fluid in.
- Fluid first fills the interstitium; lymphatics drain it until they are overwhelmed.
- The interstitium widens (Kerley lines) and then fluid floods the alveoli, beginning at the bases.
- Flooded alveoli cannot exchange gas, causing hypoxaemia and dyspnoea; the wet lung also favours infection.
- When endothelium or epithelium is injured instead, protein leaks out even at normal pressure.
Hemodynamic vs injury pulmonary edema
| Feature | Hemodynamic (cardiogenic) | Injury (noncardiogenic) |
|---|---|---|
| Main cause | Left heart failure, volume overload | Sepsis, pneumonia, aspiration, trauma, toxins |
| Fluid | Transudate, little protein | Exudate, rich in protein |
| Distribution | Bases first, dependent | Diffuse, patchy |
| Microscopy | Pale pink fluid, congested capillaries, heart failure cells | Exudate, inflammation, hyaline membranes |
| Pulmonary capillary pressure | High | Normal |
Clinical notes
- Acute cardiogenic edema: orthopnoea, paroxysmal nocturnal dyspnoea, crackles, pink frothy sputum.
- Heart failure cells in sputum or lavage point to chronic venous congestion.
- A normal wedge pressure with bilateral infiltrates suggests injury edema (ARDS).
Test yourself
Think of the answer, then tap the question to see it.
What are heart failure cells and where are they found?
Alveolar macrophages filled with hemosiderin from small hemorrhages, seen in the alveoli in chronic pulmonary venous congestion.
Why does cardiogenic edema start at the lung bases?
Hydrostatic pressure is highest in the dependent parts of the lung, so fluid leaks there first.
What is brown induration of the lung?
Firm, brown lungs from long-standing congestion: abundant hemosiderin-laden macrophages and septal fibrosis, classically in mitral stenosis.
Elsewhere in DurgiPedia
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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Lung Diseases (MedlinePlus, US National Library of Medicine, 2025); Acute Respiratory Distress Syndrome (StatPearls (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.