Acute respiratory distress syndrome (ARDS) is defined and diagnosed by the following criteria, which has been promulgated or endorsed by the European Society of Intensive Care Medicine, the American Thoracic Society, and the Society of Critical Care Medicine. It is otherwise known as the Berlin criteria for ARDS:

  • Diminished arterial partial pressure of oxygen (PaO2) relative to fraction of inspired oxygen (FIO2)
  • New or worsening respiratory distress, especially one that has occurred within one week of an injury to the lung
  • On imaging, the presence of bilateral opacities that are not fully explained by pleural effusions, pulmonary nodules, or lung collapse
  • Respiratory failure that is not fully explained by congestive heart failure or fluid overload
  • Hydrostatic edema has been satisfactorily excluded by objective assessment (e.g. echocardiography)

Severity of ARDS

The severity of ARDS is determined by the severity of the loss of arterial partial pressure of oxygen relative to fraction of inspired oxygen:

  • Mild: PaO2/FIO2 is from 201 to 300 mmHg
  • Moderate: PaO2/FIO2 is from 101 to 200 mmHg
  • Severe: PaO2/FIO2 is 100 mmHg or less

In all of the above situations the PEEP should be at least 5 cmH2O.