Berlin ARDS Criteria - Severity Classification

Classify ARDS severity using Berlin Definition 2012. All four criteria required: (1) onset <= 1 week of known insult; (2) bilateral opacities on CXR/CT not fully explained by effusions; (3) respiratory failure not explained by cardiac failure; (4) P/F ratio on PEEP >= 5 cmH2O: mild 200-300, moderate 100-200, severe < 100.