Formulas.

<div><p>Objective</p><p>To assess a comparative analysis of the ROX index, Wood-Downes-Ferrés score (WDF), p-ROXI, and the SpO<sub>2</sub>/FiO<sub>2</sub> ratio as predictors of high-flow nasal cannula (HFNC) failure in children hospitalized for bronchiolitis.</p><p>Methods</p><p>Data were extracted from the clinical trial “Comparison between HFNC and NIV in children with acute respiratory failure caused by bronchiolitis” conducted at a tertiary Brazilian hospital (Emergency Department and PICU). The inclusion criteria were children under 2 years of age admitted for bronchiolitis who developed mild to moderate respiratory distress and were eligible for HFNC therapy. Performance was determined by ROC and AUC metrics to define the best sensitivity and specificity for each variable. Children were evaluated at 0 h, 2 h, 6 h, 12 h, 24 h, 48 h, 72 h and 96 h after HFNC therapy initiation.</p><p>Results</p><p>A total of 126 patients were recruited for this analysis. The median age was 3 months. Ninety-one percent of the patients had an identified viral agent, with RSV being the most common (65%). Twenty-three percent (29/126) of patients experienced failed HFNC therapy and required mechanical ventilation. The best cutoff points at 12 hours were 4.5 for WDF (AUC = 0.83, 0.74–0.92), 8.8 for ROX (AUC = 0.7, 0.54–0.84), 1.45 for p-ROXI (AUC = 0.56, 0.38-0-74), and 269 for SpO<sub>2</sub>/FiO<sub>2</sub> (AUC = 0.64, 0.48–0.74). The scores and indices were also correlated with the PICU and hospital LOS.</p><p>Conclusions</p><p>The ROX index and WDF were the most accurate scores for assessing HFNC failure considering 12-hour cutoff points.</p><p>Trial registration number</p><p>U1111-1262-1740; <a href="https://ensaiosclinicos.gov.br/rg/RBR-104z966s" target="_blank">RBR-104z966s</a>. Date of registration: 03/01/2023.</p></div>