Introduction: High flow oxygen (HFO) can improve oxygenation and is widely used in post-extubated patients. However, no standard parameter is available to predict HFO outcomes during post-extubation. Ratio of oxygen saturation (ROX) index can effectively predict HFO outcomes in patients with acute hypoxemic respiratory failure in pre-intubated, but not post-extubated period.

Objectives: To investigate whether ROX index predicts the outcomes of HFO in post-extubated patients.

Methods: A retrospective cohort study was performed in ?18-year-old patients with acute respiratory failure receiving post-extubated HFO between 2018 and 2020. Primary outcome was successful extubation. Secondary outcomes were 28-day and hospital mortality, and hospital length of stay (LOS). Baseline characteristics, indication for intubation, respiratory and hemodynamic data 6 hours before, then 2-6, 6-12 and 12-24 hours after HFO use were collected.

Results: Of 236 patients, 196 (83%) succeeded and 40 (17%) failed extubation after HFO use. At 6-12 hours of HFO use, mean±SD of ROX indices (breaths/min)^-1 for successful and failed groups were 12.66±1.89 and 6.71±1.44, and ROX index ?9.4 was strongly associated with successful extubation (AUROC=0.99, 95%CI=0.98-1.00). ROX index ?11.1 at 2-6 hours was associated with higher 28-day and hospital mortality (AUROC=0.65, 95%CI=0.55-0.75 and AUROC=0.73, 95%CI=0.65-0.81), and ROX index at 2-6 hours was associated with shorter hospital LOS (coefficient of median=-1.33, 95%CI=-2.29 to -0.37). 

Conclusions: ROX index could predict HFO outcomes in post-extubated patients, with ROX index ?9.4 (breaths/min)^-1 at 6-12 hours of HFO use associated with successful extubation.