According to the Berlin Definition, what is the minimum PaO₂/FiO₂ ratio threshold that defines moderate ARDS?

Explanation

## Berlin Definition of ARDS **Key Point:** The Berlin Definition (2012) replaced the older American-European Consensus Conference (AECC) definition and stratifies ARDS severity by PaO₂/FiO₂ ratio measured on PEEP ≥ 5 cm H₂O. ### ARDS Severity Classification | Severity | PaO₂/FiO₂ Ratio | PEEP Requirement | Mortality | |----------|-----------------|------------------|----------| | **Mild** | 201–300 mmHg | ≥ 5 cm H₂O | ~27% | | **Moderate** | 101–200 mmHg | ≥ 5 cm H₂O | ~32% | | **Severe** | ≤ 100 mmHg | ≥ 5 cm H₂O | ~45% | **High-Yield:** Moderate ARDS is defined as PaO₂/FiO₂ **101–200 mmHg**, which means the lower threshold is ≤ 200 mmHg. The question asks for the minimum threshold that *defines* moderate ARDS, which is the lower boundary: **≤ 200 mmHg**. **Clinical Pearl:** The Berlin Definition also requires: - Acute onset (within 1 week of known insult) - Bilateral opacities on imaging (CXR/CT) not fully explained by effusions, collapse, or nodules - Respiratory failure not fully explained by cardiac failure or fluid overload **Mnemonic:** **M-O-S** = Mild (201–300), mOderate (101–200), Severe (≤100). [cite:Harrison 21e Ch 297]