Exudative phase

Typically, this lasts for the first week after the onset of symptoms. The histological changes are termed diffuse alveolar damage.5 At necroscopic examination the lungs are heavy, rigid and, when sectioned, do not exude fluid because of its high protein content. Bachofen and Wiebel were among the first to study the histopathological changes in detail in patients who died with ARDS.19 An acute stage commencing within the first 24 hours of symptoms was marked by significant proteinaceous and often markedly haemorrhagic interstitial and alveolar oedema with hyaline membranes. The hyaline membranes are eosinophilic containing fibrin, immu-noglobulin, and complement. The microvascular and alveolar barriers have focal areas of damage and the alveolar wall is oedematous with areas of necrosis within the epithelial lining, although the basal lamina is intact initially. The early endothe-lial lesions are more subtle, containing areas of necrosis and denuded spaces usually filled with fibrin clot. Neutrophils are found increasingly during the initial phases in capillaries, interstitial tissue, and progressively within airspaces.20

Table 6.1 Summary of some histopathological changes in ARDS

Exudative phase

Proliferative phase

Fibrotic phase

Macroscopic Microscopic


Heavy, rigid, dark

Hyaline membranes



Epithelial>endothelial damage

Local thrombus

Heavy, grey

Barrier disruption Oedema

Alveolar type II cell proliferation

Myofibroblast infiltration


Alveolar collapse

Alveoli filled with cells and organising matrix Epithelial apoptosis Fibroproliferation

Loss of capillaries Pulmonary hypertension





Matrix organisation

Deranged acinar architecture

Patchy emphysematous change

Myointimal thickening Tortuous vessels

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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