ROX Index

Why use it

Guides early identification of HFNC failure. Helps avoid delayed intubation (which increases mortality). Simple bedside calculation with continuous monitoring parameters.

About

The ROX (Respiratory rate-OXygenation) Index predicts the need for intubation in patients receiving high-flow nasal cannula (HFNC) for acute hypoxemic respiratory failure. It combines SpO₂/FiO₂ ratio with respiratory rate. A ROX ≥ 4.88 at 2, 6, or 12 hours is associated with low risk of intubation.

When to use

• Patients on HFNC for acute hypoxemic respiratory failure
• Serial assessment at 2, 6, and 12 hours of HFNC therapy
• Decision support for escalation to intubation

Formula

Pearls & pitfalls

• ROX ≥ 4.88 at 2, 6, or 12 hours is the validated threshold for low intubation risk.
• ROX < 3.85 at 12 hours is associated with high intubation risk.
• Trend is important: a FALLING ROX index is concerning even if still above threshold.
• Validated primarily in pneumonia patients; use with caution in other etiologies.
• FiO₂ on HFNC is estimated based on flow rate and patient inspiratory demand.
• Does not replace clinical judgment — assess work of breathing, mental status, hemodynamics.

Next steps

ROX ≥ 4.88: Low intubation risk, continue HFNC. ROX < 3.85: High risk of HFNC failure — prepare for intubation. ROX 3.85-4.88: Reassess in 1-2 hours; consider escalation if not improving.

Evidence

Derived by Roca et al. (J Crit Care 2016) in 157 patients with pneumonia on HFNC. Validated in a multicenter cohort (Roca et al., Chest 2019). ROX ≥ 4.88 associated with low intubation risk (HR 0.27).

References

1. Roca O 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. — link