How does ARDS typically present in terms of oxygenation?

Acute Respiratory Distress Syndrome (ARDS) is characterized by impaired gas exchange, which is reflected in a decreased ratio of arterial partial pressure of oxygen (PaO2) to the fraction of inspired oxygen (FiO2). The fundamental pathophysiology of ARDS involves damage to the alveolar-capillary membrane, leading to increased permeability and resultant pulmonary edema, atelectasis, and reduced lung compliance.

In ARDS, the patient experiences significant hypoxemia and requires higher levels of oxygen to maintain adequate oxygen saturation. This is represented by the decreased PaO2/FiO2 ratio, which serves as a key diagnostic criterion for ARDS severity. According to the Berlin definition, ARDS is categorized into mild, moderate, and severe based on this ratio, with decreasing values indicating worsening lung function and oxygenation status.

Normal PaO2 levels would not be consistent with ARDS, as the disorder inherently involves decreased oxygenation capacity. Similarly, an increased PaO2/FiO2 ratio would suggest improved oxygenation, which contradicts the essence of ARDS. Oxygen toxicity, while a concern in mechanically ventilated patients receiving high concentrations of oxygen, does not directly reflect the characteristic changes seen in ARDS regarding oxygenation. Thus