• 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