An observational longitudinal study of the use of ROX index to predict treatment failure in patients receiving continuous positive airway pressure for COVID‐19

INTRODUCTION Five percent of patients with COVID-19 develop the critical disease, with one of the complications being acute hypoxemic respiratory failure (AHRF) requiring advanced respiratory support. 1 In April 2020, the British Thoracic Society (BTS) issued guidance for the delivery of continuous positive airway pressure (CPAP) to patients with AHRF as a bridging therapy prior to escalation to the intensive care unit (ICU). 2 This therapy has been shown to benefit patients with AHRF due to COVID-19 in a large multi-center trial RECOVERY-RS, their findings are still awaiting peer review. 3 Evidence is needed on how to safely manage these patients outside of ICU and prevent unnecessary delay of intubation. 4 The use of ROX index (ratio of pulse oximetry/fraction of inspired oxygen to respiratory rate) was validated in 2019 to predict whether patients with AHRF can be safely managed on HFNO or if invasive mechanical ventilation (IMV) should be considered. 5 ROX index has also been studied in patients with COVID-19 on HFNO and higher values were found to be associated with HFNO success. 6,7 This study investigated whether there is an association between ROX index before starting CPAP and within the first 24 hours of starting it and our outcome measure - whether patients were weaned off or failed CPAP. Data collection was part of routine service evaluation with prior departmental approval, data analysis was retrospective and did not affect patient outcomes.