High-flow nasal cannula in COVID-19: Outcomes of application and examination of the ROX index to predict success

Background Optimal timing of mechanical ventilation in COVID-19 is uncertain. We sought to evaluate outcomes of delayed intubation and examine the ROX index ([S_pO2/F_IO2]/breathing frequency) to predict weaning from high-flow nasal cannula (HFNC) in COVID-19.

Methods: We performed a multi-centered retrospective observational cohort study of subjects with respiratory failure from COVID-19 managed with HFNC. The ROX index was applied to predict HFNC success. Subjects that failed HFNC were divided into early HFNC failure (≤48 hours of HFNC therapy prior to mechanical ventilation) and late failure (>48 hours). Standard statistical comparisons and regression analyses were used to compare overall hospital mortality and secondary endpoints including time specific mortality, need for ECMO, and ICU length of stay between early and late failure groups.

Results: 272 subjects with COVID-19 were managed with HFNC. 164 (60.3%) were successfully weaned from HFNC and 111 (67.7%) of those weaned were managed solely in non-ICU settings. ROX index >3.0 at 2, 6, and 12 hours after initiation of HFNC was 85.3% sensitive for identifying subsequent HFNC success. 108 subjects were intubated for failure of HFNC (61 early failures and 47 late failures). Mortality after HFNC failure was high (45.4%). There was no statistical difference in hospital mortality (39.3% vs. 53.2%; P=0.18) or any of the secondary endpoints between early and late HFNC failure groups. This remained true even when adjusted for covariates.

Conclusions: In this retrospective review, HFNC was a viable strategy and mechanical ventilation was avoided in the majority of subjects. In the minority that progressed to mechanical ventilation, duration of HFNC did not differentiate subjects with worse clinical outcomes. The ROX index was sensitive for the identification of subjects successfully weaned from HFNC. Prospective studies in COVID-19 are warranted to confirm these findings and to optimize patient selection for use of HFNC in this disease.