#infectious_diseases see also: [[ARDSnet ventilator settings]], [[Sepsis]] # P/F ratio - PaO2/FiO2 Ratio see: [[Oxygen delivery devices FiO2]] AKA: "Horowitz Index for Lung Function" normal ~400-500mmHg | ARDS Severity | PaO2/FiO2 | Mortality | | ------------- | --------- | --------- | | Mild | 200 – 300 | 27% | | Moderate | 100 – 200 | 32% | | Severe | < 100 | 45% | ## S/F ratio (SpO2 to FiO2 ratio) alternative to P/F ratio - An S/F ratio of 315 approximates a P/F ratio of 300. - An S/F ratio of 235 correlates with a P/F ratio of 200. ***S/F Ratio Thresholds for Specific ARDS Categories:*** | Category | S/F ratio criteria | | ------------------------------------------------- | -------------------------------------------------------------------------------------- | | Nonintubated ARDS | ≤315 on HFNC with flow of ≥30 L/min or NIV/CPAP with ≥5 cm H2O end-expiratory pressure | | Intubated ARDS | - Mild: >235 and ≤315<br>- Moderate: >148 and ≤235<br>- Severe: ≤148 | | Modified definition for resource-limited settings | ≤315 |