Evaluation of Rox Index in acute hypoxemic patients due to COVID-19 in an intermediate respiratory care unit

Background:The Rox Index (SpO2/FiO2/Respiratory Rate) has been used as a predictor of failure of high-flow nasal oxygen therapy (HFNT) in patients with acute COVID-19 hypoxemia in the ICU.There is a need to re-evaluate this instrument in other settings.Objective: To evaluate Rox index in patients with acute hypoxemia due to COVID-19 in an intermediate respiratory care unit.Methods: Retrospective observational study carried out during January and June 2022.The primary outcome was failure of HFNT and the dependent variable was the Rox index.This instrument was analyzed at baseline, 2, 4, 6 and 12 hours.The best cut-off points were found by analyzing AUCROC, sensitivity and specificity.Time-to-event analysis was performed using Kaplan-Meier curves and Log Rank test.Results: The age was 80.3 ± 7.7 and 77.8% were male.In 66.7% HFNT failed.The best measurement was 6 hours after onset with a cut-off point of 5. 05, AUCROC 0.893 [0.746-1.000;95%CI], sensitivity 92.9%, specificity 75.0%, positive predictive value 86.7% and a negative predictive value 85.7%.Conclusions: The Rox Index has been shown to be valid as an instrument for the prediction of HFNT failure with acute COVID-19 hypoxemia in the intermediate respiratory care unit studied.