• 
  

  Acute inflammation occurring as a result of either direct or indirect injury

  
  
• 
  

  Hallmark of acute phase is diffuse alveolar damage via altered permeability of pulmonary endothelial and epithelial cells

  
  
  
  
  • 
    

    Leads to accumulation of protein-rich fluid in alveoli

    
    
  • 
    

    Inactivates surfactant

    
    
  • 
    

    Leads to hypoxia and impaired lung compliance

  
  

• 
  

  P/F Ratio

  
  
  
  
  • 
    

    PaO₂/FiO₂ is a measure of oxygenation

    
    
  • 
    

    A lower P/F ratio is reflective of more impaired oxygenation

    
    
  • 
    

    Does not incorporate mean airway pressure

  
  
  
  
• 
  

  Oxygenation Index (OI)

  
  
  
  
  • 
    

    Measure of oxygenation developed for use in neonates with persistent pulmonary hypertension

    
    
  • 
    

    Recommended for use in pediatric ARDS over P/F ratio

    
    
    OI=[mean airway pressures×FiO2÷PaO2]×100
    
    

  
  

HISTORICAL DEFINITION

• 
  

  Acute lung injury (ALI)

  
  
  
  
  • 
    

    Acute onset of respiratory failure

    
    
  • 
    

    Bilateral infiltrates on chest x-ray (CXR)

    
    
  • 
    

    PaO₂/FiO₂ <300

    
    
  • 
    

    Absence of left ventricular failure

  
  
  
  
• 
  

  Acute respiratory distress syndrome (ARDS)

  
  
  
  
  • 
    

    Acute onset of respiratory failure

    
    
  • 
    

    Bilateral infiltrates on CXR

    
    
  • 
    

    PaO₂/FiO₂ <200

    
    
  • 
    

    Absence of left ventricular failure