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PATHOPHYSIOLOGY OF ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS)

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  • 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

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DEFINITIONS

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  • 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=[meanairwaypressures×FiO2÷PaO2]×100

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DIAGNOSTIC CRITERIA

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HISTORICAL DEFINITION

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  • 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

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BERLIN DEFINITION OF ARDS (2012)

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  • Respiratory failure within one week of a known clinical insult OR new or worsening respiratory symptoms

  • Bilateral opacities on CXR not explained by effusions, collapse, or nodules

  • Respiratory failure not fully explained by cardiac failure or fluid overload

  • Impaired oxygenation with positive end-expiratory pressure (PEEP) ≥5 cm H2O

    • Mild: P/F ratio 200 to 300

    • Moderate: P/F ratio 100 to 200

    • Severe: P/F ratio <100

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PEDIATRIC ACUTE LUNG INJURY CONSENSUS CONFERENCE (2015)1 (TABLE 23-1)

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  • Excluded patients with perinatal lung disease

  • Recommendation to use OI preferentially over P/F ratio as metric of severity of lung disease

  • Provision for noninvasively ventilated patients

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TABLE 23-1

PALICC Definition of ARDS

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