In ARDS terminology, how is severity classified under the Berlin criteria?

• A. Berlin criteria classify ARDS by PaO2/FiO2 ratio into mild/moderate/severe
• B. ARDS severity is determined by chest X-ray score
• C. ALI remains the preferred term for all ARDS
• D. ARDS is defined by etiology alone

Answer: (A)

In ARDS terminology, severity under the Berlin criteria is determined by how well the lungs oxygenate the blood, expressed as the PaO2/FiO2 ratio, with a minimum PEEP of 5 cm H2O. The thresholds define three levels: mild ARDS has a PaO2/FiO2 between 200 and 300, moderate ARDS between 100 and 200, and severe ARDS at 100 or less. This focus on oxygenation distinguishes severity from imaging findings or the underlying cause. The imaging pattern, timing after injury, and the presence of edema not explained by heart failure are part of the overall ARDS diagnosis, but they do not set the severity grade.