The older ATS/ERS criteria for ARDS severity does not categorize ARDS as mild, moderate, or severe. It requires an acute onset, hypoxemia (PaO2/FiO2 < 200 mm Hg), bilateral infiltrates on chest imaging, and the absence of cardiac failure. Later criteria, such as the Berlin Definition, introduce severity categories based on the PaO2/FiO2 ratio.
The classification of ARDS severity according to the older ATS/ERS criteria is not specified in terms of mild, moderate, and severe categories. Instead, this classification focused on the acute onset of the condition, the presence of hypoxemia (with a PaO2/FiO2 ratio of less than 200 mm Hg), bilateral infiltrates on chest imaging, and the absence of left atrial hypertension, which distinguishes ARDS from cardiac causes of pulmonary edema.
The question relates to an older set of criteria, and the ATS/ERS has since updated the classification to include mild, moderate, and severe ARDS based on the Berlin Definition, which uses the PaO2/FiO2 ratio thresholds to classify severity.
The provided reference information describes Respiratory Distress Syndrome (RDS) as it relates to infants, which is a different condition to Acute Respiratory Distress Syndrome (ARDS). RDS in infants is primarily due to insufficient production of pulmonary surfactant, which is critical for lung function at birth. Meanwhile, ARDS can occur in adults and children and is characterized by rapid onset of widespread inflammation in the lungs.