Acute Respiratory Distress Syndrome (ARDS)

All four within 1 week of clinical insult: acute onset; bilateral opacities not fully explained by effusion/collapse/nodule; respiratory failure not fully explained by cardiac failure (echo if doubt); PaO₂/FiO₂ on PEEP ≥5: mild 200–300, moderate 100–200, severe ≤100. Common triggers: pneumonia, sepsis, aspiration, trauma, transfusion (TRALI), pancreatitis, drowning. ABG, CXR, echo, sepsis screen.