The ARDS Definition Task Force developed a definition for Adult Respiratory Distress Syndrome (ARDS) in Berlin in 2011. This involved the European Society of Intensive Care Medicine, the American Thoracic Society and the Society of Critical Care Medicine.


Patient selection: The patient shows new or worsening respiratory symptoms.



(1) timing

(2) findings on chest imaging studies (chest X-ray or CT)

(3) origin of pulmonary edema (respiratory failure)


Timing: The onset is within 1 week of a known clinical insult.


Findings on chest imaging studies: bilateral opacities of the lung fields that cannot be fully explained by:

(1) effusions

(2) lobar or lung collapse

(3) nodular infiltrates


Origin of pulmonary edema (respiratory failure) – cannot be fully explained by:

(1) cardiac failure

(2) fluid overload


If no risk factor is present then hydrostatic edema should be excluded by an objective assessment such as echocardiography.


Once ARDS is diagnosed, it is classified by the severity of oxygenation defect.


PaO2 to FIO2 Ratio with PEEP >= 5 cm H2O

Severity of ARDS

> 300


> 200 and <= 300


> 100 and <= 200


<= 100




• Mild ARDS may be treated by noninvasive ventilation. In this case CPAP >= 5 cm H2O is used in place of PEEP.

• At altitudes above 1,000 meters the cutoffs are adjusted for barometric pressure.


adjusted ratio =

= (ratio at sea level) * (barometric pressure in mm Hg) / 760


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