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Introduction
  • Acute Respiratory Distress Syndrome (ARDS) results from acute lung injury that leads to 
    • non-cardiogenic pulmonary edema
    • respiratory distress
    • refractory hypoxemia
    • decreased lung compliance
  • Etiology
    • acute endothelial damage resulting from
      • aspiration
      • infection
      • pancreatitis
      • multiple blood transfusions
      • lung injury
      • sepsis or shock
      • major trauma
      • large surface area burns
      • fat emboli
      • thromboembolism
      • multi-system organ failure
  • Prognosis
    • high mortality rate (50% overall) is associated with ARDS even in setting of ICU
Classification
  • ARDS is represented by three phases

    Exudative phase initially hyaline membrane comprised of fibrin form
    Proliferative phase 3 days alveolar exudate resolves or organizes
    Fibrotic phase 3-4 weeks alveolar ducts and spaces undergo fibrosis
Presentation
  • Symptoms
    • acute onset (12-48 hours) of
      • dyspnea
      • fever
      • mottled or cyanotic skin
  • Physical exam
    • resistant hypoxia
    • intercostal retractions
    • rales/crackles and ronchi
    • tachypnea
Evaluation
  • Hypoxemia is refractory to O2
    • 3 different categories of ARDS based on degree of hypoxemia
    • PaO2 / FIO2 ratio < 300 mm Hg=  mild
    • PaO2 / FIO2 ratio < 200 mm Hg=  moderate
    • PaO2 / FIO2 ratio < 100 mm Hg=  severe
  • Chest xray 
    • shows patchy pulmonary edema (air space disease)
    • diffuse bilateral pulmonary infiltrates
      • normal sized heart
        • makes CHF less likely
  • Respiratory compliance (<40 mL/cm H20)
  • Positive end-expiratory pressure (>10cm H20)
  • Corrected expired volume per minute (>10L/min)
Differential
  • Cardiogenic pulmonary edema (i.e. CHF or MI), bilateral pneumonia, SARS
Treatment
  • Nonoperative
    • PEEP ventilation and steroids
    • treat the underlying pathology/disease
  • Operative
    • early stabilization of long bone fractures (femur)
  • Prevention
    • closely monitor PEEP in patients at-risk of ARDS
    • serial X-rays in concerning patients can assist in early identification and intervention
Complications
  • Pneumothorax
    • secondary to ventilator with high PEEP
 

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