Prospective validation of HACOR score for HFNO failure in emergency department patients with acute respiratory failure.

BACKGROUND: High-flow nasal oxygen (HFNO) failure occurs in 30-42% of emergency department (ED) patients with acute respiratory failure (ARF). The HACOR score was derived in intensive care patients on mask-based noninvasive ventilation; its performance during HFNO in unselected ED patients has not been prospectively validated. METHODS: Adults started on HFNO for ARF with arterial blood gas data at HFNO initiation (T0) and at 60 min (T60) were prospectively enrolled at a single tertiary academic ED. The primary outcome was HFNO failure (intubation or death from any cause within 48 h). We assessed discrimination (AUC, DeLong method), calibration (cross-validated slope) and clinical utility (decision curve analysis); the Youden-optimal T60 threshold was derived, bootstrap-corrected for optimism, and compared with the original cutoff (HACOR >5). RESULTS: Of 332 patients (median age 71 years; 47.0% male), 117 (35.2%) failed HFNO, of whom 115 (98.3%) were intubated. T60 HACOR outperformed T0 (AUC 0.890 [95% CI 0.853-0.927] vs. 0.701 [0.645-0.757]; ΔAUC +0.189; p < 0.001), showed no evidence of miscalibration (slope 0.98; calibration-in-the-large -0.001), and showed positive net benefit at threshold probabilities of 10-60%. HACOR ≥8 at T60 gave sensitivity 86.3% and specificity 76.7% (bootstrap-corrected 85.5% and 76.3%; selected in 75.5% of resamples); HACOR >5 gave sensitivity 94.9%, specificity 42.3% and NPV 93.8%. Subgroup AUCs ranged 0.856-0.912. CONCLUSION: The 60-min HACOR score discriminates HFNO failure well, with no evidence of miscalibration, in an unselected ED cohort, substantially outperforming the admission score. The >5 threshold remains the reference for ruling out failure; the ≥8 threshold derived here is exploratory and requires prospective validation.