Evaluation of the ROX index for predicting intubation in ICU patients

Background: The ROX index was proposed as a decision-support tool to assess the effectiveness of high-flow oxygen therapy (HFOT) in patients with acute hypoxemic respiratory failure (AHRF) affected by pneumonia. Objective: The purpose of this work was to assess the discriminative power of the ROX index across heterogeneous intensive care unit (ICU) populations. As a secondary, hypothesis-generating objective, we explored whether ROX-based risk stratification may provide a standardized reference for describing variability in observed intubation practices across datasets and centers. Methods: Patients affected by AHRF and receiving oxygen support were identified from two large public ICU databases (MIMIC-IV and eICU). Oxygen support was stratified based on recorded flow rates, i.e., LPMO2 ≥ 6 for conventional oxygen therapy (COT) and ≥ 30 for HFOT. All AHRF patients were initially considered, regardless of the underlying pathology, with a subgroup analysis performed in patients with pneumonia. ROX index predictions were compared with actual intubation rates in different datasets, and alternative thresholds were explored using Youden's method. Results: In the primary three-category analysis, ROX risk strata produced only modest likelihood ratios (LRs) for observed intubation. In the merged cohorts, high-risk ROX categories showed LR values ranging from 1.36 to 2.06, whereas low-risk categories showed LR values close to 1, ranging from 0.85 to 0.90. Binary cut-off analyses confirmed limited discrimination, with AUROC values between 0.56 and 0.64. Conclusions: When applied across heterogeneous real-world populations, the ROX index shows limited discriminative ability for predicting intubation and should not be used as a standalone decision tool. However, it may serve as a standardized reference to explore variability in intubation practices across centers, particularly in retrospective analyses.