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ROX index (high-flow nasal oxygen)

Also called ROX, HFNC failure index, high-flow nasal cannula ROX

(SpO₂/FiO₂)/respiratory rate to predict success or failure (intubation) of high-flow nasal cannula in pneumonia.

%
/min
Time on HFNC

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Formula and scoring

ROX = (SpO₂ ÷ FiO₂ as fraction) ÷ RR. Success ≥ 4.88 at 2, 6 or 12 h; failure < 2.85 (2 h), < 3.47 (6 h), < 3.85 (12 h).

Exam and ward pearls

  • The SpO₂/FiO₂ component carries more weight than the respiratory rate (Roca 2019).

When not to rely on it

  • Derived and validated in pneumonia with acute hypoxaemic respiratory failure on HFNC; outside that population treat the cut-offs as approximate.

Source

  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;35:200-5. doi:10.1016/j.jcrc.2016.05.022 · PMID 27481760
  2. 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):1368-76. doi:10.1164/rccm.201803-0589OC · PMID 30576221

Formula and cut-offs checked against these sources on 8 Nov 2026. Educational tool for clinicians; it does not replace clinical judgement.

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