Quantifying diffuse airspace disease on portable chest radiographs in acute respiratory failure using the RALE score

BACKGROUND: Portable chest radiographs (CXRs) obtained at presentation of acute respiratory failure (ARF) are interpreted qualitatively to assess airspace disease (ASD) and identify features consistent with acute respiratory distress syndrome (ARDS). The Radiographic Assessment of Lung Edema (RALE) score offers a semiquantitative measure of radiographic ASD, and has demonstrated prognostic value in ARDS, but its ability to quantify radiographic ASD burden across the full spectrum of ARF presentations remains uncertain. METHODS: We analyzed 4,259 portable CXRs from 814 critically ill adults with expert‑adjudicated ARF subtypes, including ARDS, at‑risk for ARDS, cardiogenic pulmonary edema, acute exacerbation of interstitial lung disease (AE‑ILD), acute‑on‑chronic hypercapnic respiratory failure, and airway‑protection intubations. Trained clinicians, blinded to clinical data, assigned RALE scores. Analyses addressed (1) whether RALE distinguishes CXRs without ASD (airway‑protection intubations and acute-on-chronic hypercapnic respiratory failure) from those with any ASD, and (2) among CXRs with ASD, whether RALE quantifies diffuse bilateral opacification, distinguishing extensive from limited parenchymal involvement. Discrimination was evaluated using receiver operating characteristic curves, with sensitivity analyses assessing the influence of image‑quality features. RESULTS: RALE scores increased stepwise from ASD absent to ASD limited to ASD diffuse, discriminated CXRs with any ASD from those without (area under the curve [AUC] 0.81, 95% confidence interval [CI] 0.77-0.85; rule‑out threshold RALE ≥ 7 yielded 96% sensitivity) and quantified diffuse bilateral opacification among ASD-positive CXRs with moderate accuracy (AUC 0.79, 95% CI 0.75-0.82). RALE distributions overlapped substantially across ARDS, cardiogenic pulmonary edema, and AE‑ILD, reflecting shared radiographic appearances rather than etiologic specificity. Suboptimal penetration inflated RALE scores and markedly reduced discrimination (AUC 0.59 vs 0.83 with adequate penetration). CONCLUSIONS: RALE quantifies radiographic ASD burden across the full spectrum of ARF at intubation - discriminating ASD-absent from ASD-present CXRs and stratifying the extent of parenchymal involvement among those with ASD. However, it did not distinguish between clinical syndromes that share similar diffuse radiographic presentations, highlighting the need to interpret RALE within the broader clinical context and ensure adequate image quality for accurate scoring. These findings reflect RALE's nature as a radiographic burden metric rather than a diagnostic classifier.