Expansion
Diffuse alveolar damage with non-cardiogenic pulmonary oedema
Expansion
Berlin definition, all four required:
- Timing: within 1 week of a known insult
- Imaging: bilateral opacities not explained by effusion, collapse or nodules
- Origin: not fully explained by cardiac failure or fluid overload
- Oxygenation: PaO2/FiO2 ratio with at least 5 cmH2O of PEEP
- Mild 200 to 300, moderate 100 to 200, severe under 100 (in mmHg)
Pathology is diffuse alveolar damage, in three phases:
- Exudative, days 1 to 7: hyaline membranes, interstitial and alveolar oedema, neutrophil infiltration, type I pneumocyte necrosis
- Proliferative, days 7 to 21: type II pneumocyte proliferation, fibroblast infiltration
- Fibrotic, beyond 3 weeks: collagen deposition and architectural distortion
“Hyaline membranes are the histological signature.”
Causes: direct (pneumonia, aspiration, inhalation, contusion, near drowning) and indirect (sepsis, the commonest, pancreatitis, massive transfusion, trauma, burns, cardiopulmonary bypass).
Management: treat the cause, and lung protective ventilation with a tidal volume of 6 ml/kg predicted body weight, plateau pressure under 30 cmH2O, and permissive hypercapnia. Prone positioning improves survival in severe disease.