ARDS

Question 1

What is ARDS?

Answer 1

Berlin definition:

• Acute, diffuse, inflammatory lung injury
• Increased alveolar capillary permeability
• loss of aerated lung tissue
• hypoxia, decreased compliance, V/Q mismatch.

Berlin criteria:

• acute onset < 1 week
• bilateral opacities on imaging
• non-cardiogenic
• CPAP/PEEP 5cmH2O
• mild (200-300) (27%), moderate (100-200) (32%), severe (<100) (45%).

Question 2

What is the Murray score?

Answer 2

scoring 0-4 for 4 parameters (2Cs and 2Ps)

C- CXR quadrants affected (#=score)
C- Compliance (ml/H2O) >80, 80-60, 60-40, 40-20, <20

P- PaO2/FiO2 ratio 300, 225, 175, 100
P- PEEP 5, 8, 12, 15

Score >3 and failure to respond to conventional Tx ->refer to ECMO

Question 3

What is the pathophysiology of ARDS?

Answer 3

1. Exudative phase (1-3d):
   - Acute inflammatory insult to epithelium. Inflammatory cytokine cascade leads to neutrophil recruitment with destruction of pulmonary vascular bed and capillary leak leading to extravascular lung water and pulmonary oedema
   - inflammatory exudate leads to inactivation of surfactant, leading to collapse and consolidation.
   - V/Q matching impaired by inflammation causing dysregulation of vascular tone.
   - Dysregulation of coagulation and fibrinolysis leading to microthrombus formation.
2. Proliferative phase (3-6d)
   - proliferation of type 2 pneumocytes and fibroblasts.
3. Fibrotic phase (2nd week)
   - Fibrosis of damaged lung tissue.

Question 4

What are the causes of ARDS?

Answer 4

Can be divided into:

1. Pulmonary:
   - Pneumonia
   - Pulmonary contusion
   - Aspiration pneumonitis
   - Inhalational injury
   - Pulmonary vasculitis
   - Drowning
2. Extrapulmonary:
   - Pancreatitis
   - severe burns
   - Sepsis
   - Major trauma
   - TRALI
   - Pump lung