Which symptom is a hallmark of acute respiratory distress syndrome (ARDS)?

Acute respiratory distress syndrome (ARDS) is characterized by severe lung inflammation and impaired gas exchange, leading to significant respiratory distress. Persistent hypoxemia, or consistently low levels of oxygen in the blood, is a hallmark symptom of ARDS due to the lungs' inability to deliver sufficient oxygen to the bloodstream. This condition arises from the direct or indirect injury to the alveolar-capillary membrane, making it difficult for oxygen to enter the bloodstream and for carbon dioxide to be expelled.

While fever and chills can be associated with various infections that might lead to ARDS, they are not specific to this syndrome. Similarly, while lethargy can occur in many patients with respiratory distress due to inadequate oxygenation, it is not unique to ARDS. Coughing up blood, or hemoptysis, may be seen in other respiratory conditions but is not a defining symptom of ARDS. The persistent hypoxemia, on the other hand, directly correlates with the fundamental problem in ARDS and marks it out as the key feature of this syndrome.