The Berlin definition (2012) replaced the American-European Consensus Conference criteria for ARDS. According to the Berlin definition, which combination correctly defines 'severe' ARDS?
- A PaO2/FiO2 ratio <300 mmHg with bilateral chest infiltrates within 7 days of insult
- B PaO2/FiO2 ratio <200 mmHg with non-cardiogenic pulmonary oedema
- C PaO2/FiO2 ratio <100 mmHg with PEEP ≥5 cm H2O and bilateral opacities on chest imaging ✓
- D PaO2/FiO2 ratio <150 mmHg regardless of PEEP settings
Correct answer: C. PaO2/FiO2 ratio <100 mmHg with PEEP ≥5 cm H2O and bilateral opacities on chest imaging
Explanation
The 2012 Berlin definition of ARDS classifies severity based on PaO2/FiO2 ratio measured with PEEP ≥5 cm H2O: mild (201–300 mmHg), moderate (101–200 mmHg), severe (≤100 mmHg). All categories require: onset within 1 week of an identifiable insult, bilateral opacities on chest X-ray or CT not fully explained by effusion/collapse/nodules, and respiratory failure not fully explained by cardiac failure or fluid overload. 'Severe' ARDS corresponds to PaO2/FiO2 ≤100 mmHg on PEEP ≥5 cm H2O, associated with the highest mortality.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
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