Definition
- A clinical syndrome characterized by inflammatory lung injury leading to acute hypoxemia and bilateral radiographic infiltrates
- Berlin Definition of ARDS
- Acute onset (within 1 week of clinical insult or worsening respiratory status)
- Bilateral infiltrates (without an alternative explanation)
- Respiratory failure not caused by cardiac causes or volume overload
- Hypoxemia
- (PaO₂/FiO₂ ratio < 200 or 26.6 kPa irrespective of PEEP)
- ARDS severity
Severity | PaO₂/FiO₂ |
Mild | 200-300 |
Moderate | 100-200 |
Severe | < 100 |
Pathology
- Early stages consist of an exudative phase of injury with associated edema. The later stage is one of repair and consists of fibroproliferative changes. Subsequent scarring may result in poor lung function.
Pathophysiology
- Alveolar insult → release of pro-inflammatory cytokines → neutrophil recruitment, activation, and release of toxic mediators (eg, reactive oxygen species, proteases, etc) → capillary endothelial damage and ↑ vessel permeability → leakage of protein-rich fluid into alveoli → formation of intra-alveolar hyaline membranes (arrows in A) and noncardiogenic pulmonary edema (normal PCWP) → ↓ compliance and V/Q mismatch → hypoxic vasoconstriction → ↑ pulmonary vascular resistance.
- Loss of surfactant also contributes to alveolar collapse (eg, preterm infants, drowning).
Aetiology
- Infection (> 40%)
- Aspiration (30%)
- Trauma (> 20%)
- Massive blood transfusion
- Smoke inhalation
- Pancreatitis
- Cardio-pulmonary bypass
- Burns.
Treatment
- The goal is to maintain gas exchange while avoiding ventilator-induced lung injury
- Done via mechanical ventilation
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