Delta ROX as a predictor of High flow nasal cannula failure in COVID-19 critically ill patients

<bold>Introduction:</bold> High-flow nasal cannula (HFNC) is commonly used in intensive care unit (ICU) to treat COVID-19–related acute hypoxemic respiratory failure (AHRF). But little is known about the factors associated with HFNC failure. <bold>Aim:</bold> Determine the reliability of the ROX index variation’s (delta ROX) to predict HFNC failure in COVID-19-related AHRF patients admitted in the ICU. <bold>Methods:</bold> A retrospective observational study, conducted in an intensive care unit of university hospital, from October 1st,2020, to December 31,2021. Patients admitted and received HFNC as a treatment for COVID-19–related AHRF were included. A multivariate analysis was used to identify the factors associated with HFNC failure. <bold>Results:</bold> A total of 134 patients were included in this study. The mean age was 50.78 ±13.54 years with male predominance, 69 (59%) patients. Median SAPS II, was 23 [16-29]. The median ICU length of stay was 9 [6-14] days. HFNC failure was found in 46 patients (34.3%). A ROX index value of less than 6 at HFNC initiation was a predictive factor associated with HFNC failure (p<0.001). The multivariate logistic regression model identified the following factors as predictors of HFNC failure: delta ROX index per day (OR, 3.8; 95% CI, [1.4-10.25]; p=0.007; SAPSII (OR, 1.09; 95% CI, [1.03- 1.16]; p=0.002 and basal lesion in CT scan (OR, 3.64; 95% CI, [1.17-11.34]; p= 0.025). <bold>Conclusion:</bold> The delta ROX index per day in COVID-19-related AHRF patients requiring HFNC was a predictor of HFNC failure. An early screening of ROX index variation in these patients can be an effective tool to predict HFNC failure in ICU.