Old and New Definitions of Acute Respiratory Distress Syndrome (ARDS): An Overview of Practical Considerations and Clinical Implications

Low respiratory tract infections remain a leading cause of morbidity and mortality among Intensive Care Unit patients, with severe cases often progressing to acute respiratory distress syndrome (ARDS). This life-threatening condition results from damage to the alveolar-capillary membrane, causing refractory hypoxemia and respiratory failure. Early detection and management are critical to treat the underlying cause, provide protective lung ventilation and, eventually, improve patients’ outcome. The Berlin definition, introduced in 2012, standardized ARDS diagnosis but excluded patients managed with non-invasive ventilation (NIV) or high-flow nasal cannula (HFNC) modalities, which are increasingly used, especially after the COVID-19 pandemic. This exclusion may delay diagnosis and treatment in patients who worsen despite non-invasive ventilatory support. Recent efforts aimed to broaden ARDS criteria by incorporating NIV and HFNC use, alongside alternative diagnostic tools like lung ultrasound and the SpO₂/FiO₂ ratio. These proposed modifications attempted to enhance the diagnosis of ARDS in resource-limited settings where access to arterial blood gas analysis or advanced imaging modalities may be restricted, thereby increasing the global applicability of ARDS classification. However, broadening the diagnostic criteria introduces several challenges, including the risk of overdiagnosis and the difficulty in differentiating ARDS from other causes of acute hypoxemic respiratory failure. Furthermore, inter-observer variability in imaging interpretation and inconsistencies in oxygenation assessment, particularly when relying on non-invasive measurements, may compromise diagnostic reliability. To address these limitations, a more nuanced diagnostic framework is needed, one that incorporates individualized therapeutic strategies, emphasizes lung-protective ventilation, and integrates advanced physiological or biomarker-based indicators. Such an approach has the potential to improve patient stratification, enable more targeted interventions, and ultimately enhance conduction of interventional trials.