ROX Index

What This Calculator Measures

Calculates the ROX index, which combines oxygenation (SpO₂/FiO₂) with respiratory rate to estimate the likelihood that high-flow nasal cannula (HFNC) therapy will succeed or fail in adults with acute hypoxemic respiratory failure.

How to Use

1. Use only in patients already receiving high-flow nasal cannula (HFNC) therapy.
2. Enter SpO₂ as a percentage (e.g., 92 for 92%), FiO₂ as a fraction (e.g., 0.6 for 60%), and the respiratory rate.
3. The index is designed to be reassessed over time during the initial hours of HFNC therapy rather than used as a one-time definitive decision.
4. Interpret the result together with the patient's clinical trajectory when deciding whether to continue or escalate respiratory support.

Interpretation Guide

ROX ≥4.88 suggests a high likelihood of HFNC success with low risk of intubation; 3.85–4.87 indicates intermediate risk warranting close monitoring and reassessment; <3.85 indicates a high risk of HFNC failure and supports earlier consideration of escalation of respiratory support.

Clinical Significance

The ROX index combines simple bedside measurements to help clinicians gauge the likelihood of HFNC success in acute hypoxemic respiratory failure, supporting earlier identification of patients who may require invasive mechanical ventilation.

When to Use

• Adults with acute hypoxemic respiratory failure receiving HFNC
• Serial monitoring of HFNC response during the initial hours of therapy
• Supporting decisions about continuing HFNC versus escalating respiratory support

When Not to Use

• Patients not receiving HFNC therapy
• Children and neonates, where the index has not been validated in the same way as in adults
• As a standalone indication for immediate intubation without clinical assessment

Limitations

• The ROX index is a dynamic assessment and must be reassessed over time; a single value is not definitive.
• It was derived and validated primarily in adults with pneumonia-related acute hypoxemic respiratory failure.
• SpO₂-based ratios can be affected by hemoglobin level, peripheral perfusion, and measurement conditions.
• It does not replace clinical judgment or account for comorbidities, work of breathing, or overall trajectory.

Worked Example

A 68-year-old man with COVID-19 pneumonia on high-flow nasal cannula has SpO₂ 85% on FiO₂ 0.8 with a respiratory rate of 30 breaths/min.

ROX = (85 / 0.8) / 30 ≈ 3.54 — high risk of HFNC failure; consider earlier escalation of respiratory support.

Evidence

Source

Original Index Description

Reference

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.

Reviewed By

MedCalcHub Clinical Team

Version

2016

Updated

2026-08

1. Roca O, et al. J Crit Care. 2016;35:200-205.

References

1. Roca O, 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. (Original index)