ROX Index Calculator
A bedside predictor of high-flow nasal cannula outcome — combining oxygenation and respiratory drive into one number, with the validated thresholds and the importance of the trend.
Written by Apex Respiratory Editorial Team
Enter as a fraction (0.5) or a percent (50).
Enter SpO₂, FiO₂, and respiratory rate to calculate the ROX index.
Reading the ROX index
ROX combines SpO₂/FiO₂ (oxygenation) with respiratory rate (drive); a higher value means better oxygenation for the breathing effort.
Validated cutoffs from Roca et al.: ROX ≥ 4.88 at 2, 6, or 12 hours of high-flow predicts HFNC success; < 3.85 flags high failure risk and argues for intubation rather than delay; 3.85–4.88 is a gray zone — recheck in 1–2 h and watch the trend. The < 3.85 failure cutoff is the 12-hour value; earlier it is lower — below 2.85 at 2 h and below 3.47 at 6 h.
It was derived and validated in acute hypoxemic respiratory failure due to pneumonia and is an adjunct to, not a replacement for, the overall clinical picture.
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Sources
- Roca O, Caralt B, Messika J, et al. An index combining respiratory rate and oxygenation to predict outcome of nasal high-flow therapy. Am J Respir Crit Care Med. 2019;199(11):1368-1376.
- Roca O, Messika J, Caralt B, et al. Predicting success of high-flow nasal cannula in pneumonia patients with hypoxemic respiratory failure: the utility of the ROX index. J Crit Care. 2016;35:200-205.