BACKGROUND: The ratio of pulse-oximetric peripheral oxygen saturation to fraction of inspired oxygen (SpO METHODS: Observational cohort study of ARDS patients from three high-resolution Intensive Care Unit databases, including our own database ICU Cockpit, MIMIC-IV (Version 3.0) and SICdb (Version 1.0.6). Patients with ARDS were identified based on the Berlin criteria or ICD 9/10-codes. Time-matched datapoints of SpO RESULTS: Overall, 708 ARDS patients were included in the analysis. ARDS severity was misclassified by SpO CONCLUSIONS: The use of SpO