Highlights
• A 20-year retrospective analysis of 205,393 mechanically ventilated ARDS admissions reveals mortality declined during the ICD-9 era (OR 0.96/year) but paradoxically increased during the ICD-10 period (OR 1.05/year).
• The ICD-10 cohort demonstrated greater comorbidity burden and higher prevalence of pulmonary ARDS etiology, potentially explaining the mortality reversal.
• Hospitalization costs and length of stay improved during ICD-9 but plateaued in the ICD-10 era, reflecting increasing complexity of surviving patients.
• These findings underscore the critical importance of accounting for coding transitions and patient case-mix when interpreting longitudinal ARDS outcomes.
