ARDS defination
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"acute respiratory distress syndrome" AND "Berlin definition"
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ARDS Berlin definition criteria table PaO2/FiO2 ratio
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Here is a thorough summary of the ARDS definition based on Fishman's Pulmonary Diseases and Disorders:
Acute Respiratory Distress Syndrome (ARDS) - Definition
Historical Background
- 1967 - Ashbaugh et al. first described the syndrome: acute onset of dyspnea, severe hypoxemia, diffuse lung infiltrates, and decreased respiratory compliance in the absence of congestive heart failure (CHF). Initially called "acute respiratory distress in adults."
- 1988 - Murray et al. introduced the Lung Injury Score (LIS), incorporating PaO2/FiO2 ratio, respiratory compliance, PEEP level, and extent of radiographic infiltrates (score ≥2.5 = severe disease).
- 1994 - American-European Consensus Conference (AECC) standardized definitions:
- Acute lung injury (ALI): PaO2/FiO2 ≤300
- ARDS: PaO2/FiO2 ≤200
- Plus bilateral infiltrates and no evidence of left atrial hypertension.
The Berlin Definition (2012) - Current Standard
An international expert panel convened in Berlin in 2012 to address limitations of the AECC definition. According to the Berlin Definition, ARDS is defined as a syndrome characterized by all four of the following criteria:
| Criterion | Details |
|---|---|
| 1. Timing | Onset within 1 week of a known clinical insult or new/worsening respiratory symptoms |
| 2. Chest Imaging | Bilateral opacities on CXR/CT not fully explained by pleural effusions, atelectasis, or nodules |
| 3. Origin of Edema | Respiratory failure not fully explained by cardiac failure or fluid overload (objective assessment needed to exclude hydrostatic edema if no risk factor present) |
| 4. Oxygenation | PaO2/FiO2 ≤300 mmHg with PEEP or CPAP ≥5 cmH2O |
Severity Classification (Berlin Definition)
| Severity | PaO2/FiO2 Ratio | PEEP Requirement |
|---|---|---|
| Mild | 200 < PaO2/FiO2 ≤ 300 mmHg | PEEP or CPAP ≥5 cmH2O |
| Moderate | 100 < PaO2/FiO2 ≤ 200 mmHg | PEEP ≥5 cmH2O |
| Severe | PaO2/FiO2 ≤ 100 mmHg | PEEP ≥5 cmH2O |
Note: The old term "Acute Lung Injury (ALI)" is now obsolete and replaced by Mild ARDS.
Key Improvements of Berlin Over AECC
- "Acute" is defined - onset must be within 1 week (previously not time-bounded)
- Chest radiograph criteria clarified - explicitly excludes opacities due to effusions, atelectasis, or nodules
- PEEP standardized - PaO2/FiO2 must be measured with PEEP/CPAP ≥5 cmH2O (removes variability from ventilator settings)
- Heart failure exclusion - requires objective assessment (e.g., echocardiography) if no clear ARDS risk factor is present
- Three severity categories - mild/moderate/severe, which correlate with mortality risk
- ALI term eliminated - replaced by "mild ARDS"
Epidemiology & Mortality (context)
- Estimated US incidence: ~190,000 cases/year
- Mortality: mild ~27%, moderate ~32%, severe ~45% (Berlin validation cohorts)
- Common risk factors: sepsis, pneumonia, aspiration, major trauma, transfusions (TRALI), pancreatitis
Source: Fishman's Pulmonary Diseases and Disorders, Chapter 141 - Acute Respiratory Distress Syndrome: Clinical Features, Management, and Outcomes
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