Acute Respiratory Distress Syndrome (ARDS) 

Definition: 
ARDS is a severe, sudden lung condition where fluid leaks into the alveoli (tiny air sacs in the lungs), leading to severe shortness of breath and low oxygen levels in the blood. It is often a complication of another underlying condition. 

Causes / Risk Factors 

Sepsis (most common cause) 
Severe pneumonia 
Trauma (especially chest trauma) 
Aspiration (inhaling vomit or other substances) 
Pancreatitis 
Severe burns or blood transfusions 

Pathophysiology 

Injury to the alveolar-capillary membrane → increased permeability 
Fluid leakage into alveoli → pulmonary oedema (non-cardiogenic) 
Reduced gas exchange → hypoxemia (low oxygen in blood) 
Stiff lungs → difficulty in ventilation 

Clinical Features 

Rapid onset of severe shortness of breath 
Tachypnoea (fast breathing) 
Hypoxemia (low oxygen saturation) 
Bilateral infiltrates on chest X-ray (not explained by heart failure) 
Diagnosis (Berlin Criteria) 
Timing: Within 1 week of a known clinical insult 
Chest imaging: Bilateral opacities not explained by effusions, collapse, or nodules 
Origin of oedema: Not fully explained by cardiac failure or fluid overload 

Oxygenation (PaO₂/FiO₂ ratio): 

Mild ARDS: 200–300 mmHg 
Moderate ARDS: 100–200 mmHg 
Severe ARDS: <100 mmHg 
 
Treatment 

Supportive care is mainstay: 

Mechanical ventilation with low tidal volumes (lung-protective ventilation (6ml/kg IBW)) 
Positive end-expiratory pressure (PEEP) to keep alveoli open 
Treat underlying cause (e.g., antibiotics for infection) 
Adjunct therapies: Prone positioning to improve V/Q, neuromuscular blockers, ECMO in severe cases 
 
Prognosis 

Mortality: ~30–40%, depending on severity and comorbidities 
Long-term: Some survivors have reduced lung function, fatigue, or cognitive issues as a consequence of prolonged illness and hypoxia