Acute respiratory distress syndrome
Formal Definition
A syndrome of acute, severe hypoxemic respiratory failure due to non-cardiogenic pulmonary edema; defined by Berlin criteria: bilateral opacities on CXR, PaO2/FiO2 ratio ≤300, PaO2 ≤300 mmHg on PEEP ≥5 cmH2O, within 1 week of known clinical insult; caused by increased capillary permeability leading to protein-rich fluid filling the alveoli.
How It's Used on the Ward
ARDS or acute respiratory distress syndrome or wet lung — severe lung injury with fluid-filled alveoli, very difficult to oxygenate; common in sepsis, trauma, pancreatitis.
Example
"Septic patient on ventilator with PaO2 68 on FiO2 80%, PEEP 12. Bilateral diffuse infiltrates on CXR, fluid balance positive 6L. BNP normal, no history of heart failure. Diagnosis: ARDS, moderate (PaO2/FiO2 85). Ventilator adjusted to lower tidal volumes (6 mL/kg ideal body weight), plateau pressures kept <30. Prone positioning for 16h to improve V/Q matching."
Clinical Context
Berlin classification: mild (200-300), moderate (100-200), severe (<100). Management: lung-protective ventilation (low tidal volume 6 mL/kg ideal body weight, plateau pressure <30 cmH2O), PEEP titration (higher PEEP for severe ARDS per ARDSnet tables), prone positioning (improves survival in severe ARDS, 16h/day), neuromuscular blockade (24-48h in early severe), conservative fluid strategy after hemodynamic stability achieved. ECMO: for severe refractory hypoxemia. Etiologies: sepsis (most common), aspiration, trauma, pancreatitis, transfusion — treat the underlying cause simultaneously.