Predicting High-Flow Nasal Oxygen Failure at 30 Minutes Using a Physiology-Informed Dual-Domain Model

This prospective, single-center, two-stage translational study develops and validates a physiology-informed dual-domain model for ultra-early (30-minute) prediction of high-flow nasal oxygen (HFNO) failure in patients with acute hypoxemic respiratory failure. The study includes a physiological validation cohort (n=24) to anchor the EIT-derived Flow Index (EFI) as a marker of inspiratory effort, followed by a temporally separated clinical derivation cohort (n=57) and independent validation cohort (n=58). Candidate predictors are screened from 1,328 clinical features. The final dual-domain model integrates persistent physiological burden (baseline PaCO₂ and 30-minute EFI) with short-term dynamic adaptation (ΔRR and ΔSpO₂ over 30 minutes). The model's discrimination is tested prospectively without refitting.

Inclusion Criteria (must meet all): * Age ≥18 years * Acute hypoxemic respiratory failure (AHRF) requiring HFNO initiation * At least one of the following high-risk criteria: a) PaO₂/FiO₂ ≤200 mmHg or FiO₂ ≥0.40 to maintain SpO₂ ≥92%; b) Respiratory rate ≥25/min; c) APACHE II score ≥12; d) Bilateral infiltrates on chest imaging Exclusion Criteria: * Neuromuscular disease affecting spontaneous breathing * Pregnancy * Contraindication to EIT (e.g., chest wall wounds, pacemaker) * Do-not-intubate order * Hypercapnic respiratory failure as primary diagnosis (PaCO₂ \>50 mmHg with pH \