External validation of the HACOR score and ROX index for predicting treatment failure in patients with coronavirus disease 2019 pneumonia managed on high-flow nasal cannula therapy: a multicenter retrospective observational study in Japan.

In COVID-19 patients receiving HFNC therapy in Japan, the predictive performance of the HACOR score and ROX index at the 2-h time-point may be inadequate. Furthermore, clinicians should be mindful of time-point scores owing to the variation of the models' predictive performance with the time-point. Trial registration UMIN (registration number: UMIN000050024, January 13, 2023).