ROX Index Calculator
Calculate the adult HFNC ROX Index from SpO₂, explicit FiO₂, and respiratory rate for a single assessment or a 2-, 6-, and 12-hour trend.
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ROX Index calculator
[2]Calculate one time-specific ROX score or compare explicitly entered 2-, 6-, and 12-hour values. Each point requires its own SpO₂, FiO₂, FiO₂ representation, and respiratory rate; nothing is carried forward.
Roca 2019 timing-specific source context
| HFNC timing | Failure-associated lower threshold | Intermediate source range | Lower-intubation-risk association |
|---|---|---|---|
| 2 hours | <2.85 | 2.85 to <4.88 | ≥4.88 |
| 6 hours | <3.47 | 3.47 to <4.88 | ≥4.88 |
| 12 hours | <3.85 | 3.85 to <4.88 | ≥4.88 |
These source thresholds do not create a universal normal range or a stand-alone intubation decision. Immediate clinical deterioration and independent airway indications override the score.
About
This ROX Index calculator divides the pulse-oximetry saturation to inspired-oxygen ratio by respiratory rate for an adult receiving high-flow nasal cannula (HFNC). It accepts FiO₂ explicitly as percent or fraction and supports a single assessment or a 2-, 6-, and 12-hour trend. [1, 2]
The original and validation cohorts concerned adults with pneumonia-associated acute hypoxemic respiratory failure treated with HFNC. This page does not assume that the same thresholds perform identically in COVID-19, COPD or hypercapnic failure, NIV, post-extubation HFNC, immunocompromised, heterogeneous ICU, or pediatric populations. [1, 2, 6, 7]
ROX is not a diagnosis, a universal “normal range,” or a stand-alone intubation rule. Clinical deterioration or an independent airway need should not wait for an online score.
Interpretation
ROX interpretation, trend use, and limits
Why timing changes the threshold
The 2019 validation evaluated ROX at 2, 6, and 12 hours after HFNC initiation. The low-side failure-associated threshold increased from 2.85 to 3.47 to 3.85, while 4.88 or higher at each time was associated with lower intubation risk. These are source-cohort associations, not universal outcome guarantees. [2, 3]
Why serial ROX values are shown
Roca 2019 reported that people in whom HFNC failed had a smaller ROX increase over 12 hours. The serial mode therefore shows each exact time-specific result and the arithmetic change from the preceding entered point. It does not infer improvement, deterioration, success, failure, or a treatment action from direction alone. [2]
No single universal cutoff
Later studies and pooled analyses used different populations, assessment times, and cutoffs. A 2022 pneumonia meta-analysis found overall predictive utility but substantial study variation, while a 2026 heterogeneous-ICU external validation found only modest discrimination and advised against stand-alone use. [6, 7]
Current respiratory-support boundary
ERS guidance addresses HFNC as a respiratory-support modality rather than validating one ROX action threshold. ESICM 2023 explicitly identified uncertainty about how long an HFNO trial should last and whether ROX or another index should indicate HFNO failure and need for intubation. This calculator therefore reports source-labeled evidence context without selecting escalation, ventilation, or treatment. [4, 5]
ROX versus related oxygenation tools
| Tool | Required oxygen measure | Distinct task |
|---|---|---|
| ROX Index | SpO₂, FiO₂, respiratory rate | HFNC response-monitoring context; calculated here. |
| P/F ratio | Arterial PaO₂ and FiO₂ | Arterial oxygenation ratio and support-specific ARDS context. |
| Oxygenation Index | FiO₂, mean airway pressure, PaO₂ | Ventilated-patient pressure-adjusted oxygenation index. |
Worked examples
- SpO₂ 95%, FiO₂ 50% (0.50), RR 20 → S/F 190 and ROX 9.5.
- SpO₂ 97.6%, FiO₂ 50% (0.50), RR 40 → ROX exactly 4.88.
- SpO₂ 85.5%, FiO₂ 75% (0.75), RR 40 → ROX exactly 2.85.
Examples demonstrate the validated arithmetic and exact boundaries; they are not predictions for an individual person.
References
- 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. PMID 27481760. DOI 10.1016/j.jcrc.2016.05.022.
- 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. PMID 30576221. DOI 10.1164/rccm.201803-0589OC.
- Roca O, Caralt B, Messika J, et al. Reply to Tatkov, to Karim and Esquinas, and to Tulaimat. Am J Respir Crit Care Med. 2019;200(1):117–119. DOI 10.1164/rccm.201903-0571LE.
- Oczkowski S, Ergan B, Bos L, et al. ERS clinical practice guidelines: high-flow nasal cannula in acute respiratory failure. Eur Respir J. 2022;59(4):2101574. PMID 34649974. DOI 10.1183/13993003.01574-2021.
- Grasselli G, Calfee CS, Camporota L, et al. ESICM guidelines on acute respiratory distress syndrome: definition, phenotyping and respiratory support strategies. Intensive Care Med. 2023;49(7):727–759. PMID 37326646. DOI 10.1007/s00134-023-07050-7.
- Zhou X, Liu J, Pan J, Xu Z, Xu J. The ROX index as a predictor of high-flow nasal cannula outcome in pneumonia patients with acute hypoxemic respiratory failure: a systematic review and meta-analysis. BMC Pulm Med. 2022;22(1):121. PMID 35365110. PMCID PMC8972647. DOI 10.1186/s12890-022-01914-2.
- Angelucci A, Aliverti A, Pradella I, et al. Evaluation of the ROX index for predicting intubation in ICU patients. Int J Med Inform. 2026;219:106560. PMID 42361437. DOI 10.1016/j.ijmedinf.2026.106560.
FAQ
In Roca 2019, values below 2.85 at 2 hours, below 3.47 at 6 hours, and below 3.85 at 12 hours were failure-associated thresholds; 4.88 or higher at each time was associated with lower intubation risk. Values between those limits were intermediate source ranges. These cohort associations are not universal action rules.
The 2019 validation assessed ROX at 2, 6, and 12 hours and found less increase over time among people in whom HFNC failed. Serial mode displays each time-specific score and the exact arithmetic change, but it does not infer success, failure, or a treatment decision from direction alone.
Sources: [2]
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Disclaimer
Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.