The new 2012 definition for Acute Respiratory Distress Syndrome (ARDS) (published in JAMA June 2012)
According to the previous definition published in 1994 by the American-European Consensus Conference (AECC), ARDS must have the following 4 criteria:
- the onset must be acute
- there must be hypoxemia with PaO2/FIO2 ratio ≤ 200
- there must be bilateral infiltrates on CXR
- these findings cannot be attributed to other causes
However, a number of problems are found with the 1994 definition, including:
- term 'acute' was not defined (i.e., how "acute" is acute)
- the category of ratio PaO2/FIO2 between 201-300 is confusing (PaO2/FIO2 ≤ 300 is ALI, PaO2/FIO2 ≤ 200 is ARDS, PaO2/FIO2 between 201 - 300 ?ALI/ARDS)
- CXR interpretation has poor inter-observer reliability
With this, the new Berlin 2012 definition of ARDS is published with the following changes:
- the category of acute lung injury (ALI) with PaO2/FIO2 ≤ 300 is REMOVED
- instead, ARDS is now divided into three categories based on severity of hypoxemia
- PaO2/FIO2 between 200–300 is defined as mild
- PaO2/FIO2 between 101 - 199 is defined as moderate
- PaO2/FIO2 of less than 100 is defined as severe
- The term 'acute' now has a specified time frame of symptoms developing within ONE week of a known clinical insult
- Other changes:
- the CXR criteria is now more defined with the added phrase "bilateral opacities - not fully explained by effusions, lobar/lung collapse, or nodules"
- PCWP reading is no longer required as part of the diagnosis as this is increasingly not used. Instead, this new definition requires that the respiratory failure cannot be explained fully by cardiac failure or volume overload.
Editorial comment in JAMA June 2012 points out that this new definition only improves its predictive value of mortality slightly; however, the clarity of the criteria is significantly improved.
Ref:The ARDS Definition Task Force. Acute respiratory distress syndrome: The Berlin definition. JAMA 2012 Jun 20; 307:2526