Early Variation of ROX Index Predicts High-Flow Nasal Cannula Outcome in Awake Subjects With Severe Hypoxemic COVID-19

Introduction

A recent study¹ in the United Kingdom with more than 20,000 subjects hospitalized for COVID-19–related acute respiratory failure (ARF) showed that high-flow nasal cannula (HFNC) was the most frequently used (55%) type of respiratory support, followed by noninvasive ventilation (NIV, 16%), whereas invasive mechanical ventilation was used in only 9% of subjects. A randomized controlled trial showed HFNC was beneficial in preventing intubation.² However, another randomized controlled trial found CPAP as an initial oxygenation strategy was superior to standard oxygen therapy, whereas no differences were found compared to HFNC.³ However, these subjects were not ventilated in the prone position, which may potentiate the effect of NIV in awake subjects.^4,5 Ehrmann et al⁶ recently showed in a multinational meta-trial that awake prone positioning reduced the risk of treatment failure and the need for intubation in subjects receiving HFNC for COVID-19–related ARF.

In this context, early prediction of HFNC outcome may help with management of hypoxemic patients with COVID-19 regarding clinical decisions on optimal setting and magnitude of treatment. The ROX index, corresponding to the ratio of S_pO2/F_IO2 to breathing frequency, has been validated by Roca et al⁷ in subjects with ARF and pneumonia under HFNC, outside the COVID-19 context and without prone position. More recently, a few studies evaluated the ROX index in the setting of COVID-19–related ARF since prone position has become a standard of care.^8-10 In this observational study, we assessed the performance of the ROX index calculated upon admission and its variation over the first 12 h in the prediction of HFNC failure in subjects with COVID-19–related ARF.