Meet the New ARDS: Expert panel announces new definition, severity classes - PulmCCM
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Dec 302012
 
mechanical ventilation review jama free full text critical care review ards review  Meet the New ARDS: Expert panel announces new definition, severity classes
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A consensus panel led by V. Marco Ranieri, Gordon Rubenfeld, Arthur Slutsky et al announced a new definition and severity classfication system for acute respiratory distress syndrome (ARDS) that aims to simplify the diagnosis and better prognosticate outcomes from the life-threatening pulmonary illness.

The proposed “Berlin definition” predicted mortality ever-so-slightly better than the existing definition (created at the 1994 American-European Consensus Conference/AECC), when applied to a cohort of 4,400 patients from past randomized trials. The Berlin definition would include the following:

  • “Acute lung injury” no longer exists. Under the Berlin definition, patients with PaO2/FiO2 200-300 would now have “mild ARDS.”
  • Onset of ARDS (diagnosis) must be acute, as defined as within 7 days of some defined event, which may be sepsis, pneumonia, or simply a patient’s recognition of worsening respiratory symptoms. (Most cases of ARDS occur within 72 hours of recognition of the presumed trigger.)
  • Bilateral opacities consistent with pulmonary edema must be present but may be detected on CT or chest X-ray.
  • There is no need to exclude heart failure in the new ARDS definition; patients with high pulmonary capillary wedge pressures, or known congestive heart failure with left atrial hypertension can still have ARDS. The new criterion is that respiratory failure simply be “not fully explained by cardiac failure or fluid overload,” in the physician’s best estimation using available information. An “objective assessment“– meaning an echocardiogram in most cases — should be performed if there is no clear risk factor present like trauma or sepsis.

The new Berlin definition for ARDS would also categorize ARDS as being mild, moderate, or severe:

 ARDS Severity   PaO2/FiO2*   Mortality** 
Mild 200 – 300 27%
Moderate 100 – 200 32%
Severe < 100 45%
 *on PEEP 5+;  **observed in cohort

There is no change in the underlying conceptual understanding of ARDS as an “acute diffuse, inflammatory lung injury, leading to increased pulmonary vascular permeability, increased lung weight, and loss of aerated lung tissue…[with] hypoxemia and bilateral radiographic opacities, associated with increased venous admixture, increased physiological dead space, and decreased lung compliance.”

Although the authors emphasize the increased power of the new Berlin definition to predict mortality compared to the AECC definition, in truth it’s still poor, with an area under the curve of only 0.577, compared to 0.536 for the old definition.

Clinical variables that are widely believed to be important and useful in the management of ARDS — static compliance of the respiratory system, radiographic severity, PEEP > 10, and corrected expired volume >10L/min — were not predictive of mortality or other clinical outcomes. After including these variables in the initial draft definition and testing them empirically in the cohort, they were all dropped from the final Berlin definition for ARDS.

Authors did find a post-hoc “high risk profile” of patient with a 52% mortality from ARDS. These patients had severe ARDS (PaO2/FiO2 ratio < 100) and either a static compliance of <= 20 mL/cm H2O or a corrected expired volume of >= 13 L/min.

What was wrong with the old definition of ARDS: 1) acute onset of hypoxemia with PaO2 / FiO2 ratio <= 200 mm Hg, 2) bilateral infiltrates on chest X-ray, with 3) no evidence of left atrial hypertension ?

  • No explicit criteria for defining “acute” — leading to ambiguity regarding cases of acute-on-chronic hypoxemia.
  • High interobserver variability in interpreting chest X-rays.
  • Difficulties identifying / ruling out cardiogenic or hydrostatic pulmonary edema, especially in an era of plummeting pulmonary artery catheter use.
  • PaO2 / FiO2 ratio is sensitive to changes in ventilator settings.

The panel’s findings, endorsed by the European Society of Intensive Care Medicine, the American Thoracic Society (ATS) and the Society of Critical Care Medicine (SCCM), emerged from meetings in Berlin to try to address the limitations of the earlier AECC definition. Authors published their results in the May 21 2012 online edition of JAMA.

The ARDS Definition Task Force. Acute Respiratory Distress Syndrome. The Berlin Definition. JAMA online May 21, 2012.

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  17 Responses to “Meet the New ARDS: Expert panel announces new definition, severity classes”

  1. very good update on ARDS

  2. This makes more sense and its much easier to explain to junior staff

  3. great explanation for an ITU nurse

  4. Recognizing that LVF may coexist is important..so many older patients develop it along with ARDS

    • Good point Dr Chhabra. I think everyone now acknowledges the common sense notion that someone can have both ARDS and CHF simultaneously, and this definition helps clarify that previous confusion. Thanks for commenting.

  5. this seems to be much more practical as measuring PCWP is not possible in many cases. Coming to the radiographic part if a pulmonologist is interpreting Xray the interobserver variability will be low.

    • praveen — Yes I agree, and it never made sense that you “couldn’t” have ARDS just because left ventricular dysfunction was present — of course those patients get ARDS too. Thanks for writing. -Matt

  6. Very informative and practical review on ARDS, this will further improve early diagnosis of ARDS and optimise the treatment for patients.

  7. very informative . thanks for the update

  8. Very practical update and will ease early diagnosis and management of ARDS.

  9. a more practical approach to define….ARDS. Thanks for the updates..

  10. thank you for promotion of new knowledge that help us in dealing with our patients

  11. As a suffer a don’t think there is what is classed as mild when it comes to bronchial sepsis ards

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