Evaluation of the ROX index for predicting intubation in ICU patients

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.

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.

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.

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.

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.