ROX index

ROX index

ROX index is used to predict the success (and failure) of high-flow nasal cannula (HFNC). ROX index is the ratio of pulse oximetry/fraction of inspired oxygen (FIO2) to respiratory rate.

ROX index of 4.88 or measured after 12 hours of HFNC was associated with a lower risk of mechanical ventilation. This was noted in a study conducted on 157 patients with pneumonia [1]. It was a 4 year observation two center cohort study including patients with severe pneumonia treated with HFNC. 44 patients who needed mechanical ventilation was considered as HFNC failures.

HFNC can delivered up to 60 litres of flow with humidified and warmed oxygen using a special bedside equipment and a large nasal cannula. Fractional inspired oxygen concentration can be increased up 100% from the 21% available in room air. Due to the large flow, dilution by room air as occurs with conventional nasal oxygen cannula is minimised. This is especially so in patients with respiratory distress who have high minute volumes which tend to dilute oxygen delivered by nasal oxygen by sucking in additional room air.


  1. Roca O, Messika J, Caralt B, García-de-Acilu M, Sztrymf B, Ricard JD, Masclans JR. Predicting success of high-flow nasal cannula in pneumonia patients with hypoxemic respiratory failure: The utility of the ROX index. N Engl J Med. 2015 Jun 4;372(23):2185-96.