Predictive Factors for Tracheal Intubation in Patients with Coronavirus Disease 2019 Treated Using a High-flow Nasal Cannula

[Background] : In Japan, patients with coronavirus disease 2019 (COVID-19)* requiring a high-flow nasal cannula (HFNC) are often initially treated in non-specialized facilities and transferred to an intensive care unit if tracheal intubation is required. We aimed to investigate the factors associated with severe respiratory failure requiring tracheal intubation at an early stage in patients with COVID-19 treated using HFNCs. [Methods] : This retrospective cohort study compared the clinical features of consecutively enrolled patients with polymerase chain reaction-confirmed severe acute respiratory syndrome coronavirus-2 infection admitted to two centers in Japan between early February 2020 and late June 2021. [Results] : A total of 35 patients with COVID-19 treated using HFNCs were included. Treatment success and failure occurred in 25 and 10 patients, respectively. The oxygen saturation (ROX) index (ratio of oxygen saturation [SpO2] to fraction of inspired oxygen [FiO2] and the respiratory rate) 12 h post-HFNC insertion was a useful predictor of HFNC failure (success group, 8.0 ; failure group, 6.5 : P = 0.0005). Moreover, the time from symptom onset to respiratory failure was significantly shorter in the failure group than in the success group (3.0 and 5.0 days, P= 0.004). [Conclusions] The ROX index and time from symptom onset to respiratory failure were useful predictors of HFNC failure.