ROX Index — High-Flow Nasal Oxygen (HFNO) Success Predictor

The ROX Index (Respiratory OXygenation Index) predicts the risk of high-flow nasal oxygen (HFNO or HFNC — high-flow nasal cannula) therapy failure requiring escalation to endotracheal intubation in patients with acute hypoxemic respiratory failure (AHRF), primarily in pneumonia and COVID-19. Formula: ROX = (SpO₂ / FiO₂) / Respiratory Rate. A ROX Index ≥ 4.88 at 2, 6, or 12 hours into HFNO therapy predicts HFNO success (avoiding intubation). Originally derived and validated by Roca et al. in pneumonia patients, with extensive subsequent validation in COVID-19.