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"acute respiratory distress syndrome" AND definition
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Acute Respiratory Distress Syndrome (ARDS) - Definition
Core Definition
ARDS is a syndrome of acute, hypoxemic respiratory failure marked pathologically by diffuse alveolar damage, with resulting increased lung permeability and diffuse alveolar edema. It can arise from direct lung injury (aspiration, pneumonia) or from extrapulmonary insults (sepsis, trauma).
- Barash's Clinical Anesthesia, 9e, p. 4842
Historical Context
Before 1994: No uniform definition existed. Studies used inconsistent criteria.
1994 - AECC Definition (American-European Consensus Conference):
- Acute onset + bilateral chest infiltrates + poor oxygenation + no evidence of left atrial hypertension
- Classified as ALI (Acute Lung Injury) when PaO₂/FiO₂ ≤300, and ARDS when PaO₂/FiO₂ ≤200
- Problems: "acute" was not time-defined; chest X-ray interpretation was variable; PaO₂/FiO₂ varied with PEEP; excluding heart failure was unreliable
2012 - The Berlin Definition (current standard):
An international expert panel convened in Berlin revised the AECC definition to address its ambiguities.
- Fishman's Pulmonary Diseases and Disorders, 2-Volume Set
Berlin Definition (2012) - Diagnostic Criteria
| Criterion | Requirement |
|---|---|
| Timing | Acute onset within 7 days of a known clinical insult or new/worsening respiratory symptoms |
| Imaging | Bilateral opacities on CXR not fully explained by pleural effusions, atelectasis, or nodules |
| Cause of opacities | Not fully attributable to cardiac failure or fluid overload (requires objective assessment if no risk factor present) |
| Oxygenation | PaO₂/FiO₂ ≤300 mmHg with PEEP or CPAP ≥5 cm H₂O |
Severity Classification (Berlin Definition)
| Category | PaO₂/FiO₂ | PEEP |
|---|---|---|
| Mild | 200-300 mmHg | ≥5 cm H₂O |
| Moderate | 100-200 mmHg | ≥5 cm H₂O |
| Severe | ≤100 mmHg | ≥5 cm H₂O |
Note: The term ALI (Acute Lung Injury) is now obsolete. What was previously called ALI is now classified as "Mild ARDS" under the Berlin definition.
- Fishman's Pulmonary Diseases and Disorders | Barash's Clinical Anesthesia, 9e
Pathological Phases
ARDS progresses through three phases:
- Exudative phase - early, protein-rich alveolar edema, hyaline membranes
- Fibroproliferative phase - inflammatory infiltrate, early fibrosis
- Fibrotic phase - late-stage scarring (not all patients reach this)
Epidemiology
-
Accounts for 10-15% of all ICU admissions
-
Sepsis is the most common cause and carries ~30% risk of developing ARDS
-
Mortality varies widely: trauma patients ~10-15%; sepsis-associated ARDS is higher
-
Most deaths in ARDS patients are from the underlying condition (sepsis, trauma), not from hypoxemia per se
-
Barash's Clinical Anesthesia, 9e, p. 4843
Key Causes (Triggers)
Direct (pulmonary):
- Aspiration of gastric contents
- Pneumonia (bacterial, viral, fungal)
- Pulmonary contusion
- Inhalation injury
Indirect (extrapulmonary):
- Sepsis (most common)
- Multiple trauma
- Pancreatitis
- Massive transfusion / transfusion-related acute lung injury (TRALI)
Recent evidence note: A 2026 systematic review (PMID 41906154, Critical Care) on ARDS complications and a 2024 meta-analysis on ARDS mortality in Latin America (PMID 38635486) do not contradict the Berlin definition - the 2012 Berlin criteria remain the current standard for diagnosis.
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