Updated: 12/31/2019

Acute Respiratory Distress Syndrome (ARDS)

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Snapshot
  • A 46-year-old woman is admitted to the medical intensive care unit with severe pancreatitis. During the first 72 hours of admission, she becomes confused with increased work of breathing. Her oxygen saturation is 82% and physical exam is remarkable for tachypnea, nasal flaring, and abdominal contractions. She is placed on mechanical ventilation. A chest radiograph demonstrates bilateral infiltrates with no evidence of cardiomegaly or pleural effusions.
Introduction
  • Definition
    • a clinical syndrome characterized by inflammatory lung injury leading to acute hypoxemia and bilateral radiographic infiltrates
      • Berlin Definition of ARDS
        • acute onset (within 1 week of clinical insult or worsening respiratory status)
        • bilateral infiltrates (without an alternative explanation)
        • respiratory failure not caused by cardiac causes or volume overload
        • hypoxemia
      • ARDS severity
        • mild
          • PaO2/FiO2 is 200-300
        • moderate
          • PaO2/FiO2 is 100-200
        • severe
          • PaO2/FiO2 is < 100
  • Etiology
    • pneumonia (most common risk factor)
    • aspiration
    • pulmonary contusion
    • acute pancreatitis
    • sepsis
  • Pathogenesis
    • injury and inflammation to the alveoli increases pulmonary capillary permeability
      • phases 
        • exudative
          • immune-mediated destruction of the epithelial-interstitial-endothelial barrier
            • allows fluid into the interstitium and airspace
        • proliferative
          • recovery of the destroyed barrier
        • fibrotic
          • impaired removal of alveolar collagen that was produced during the early injury process limits functional recovery
    • impaired gas exchange
  • Prognosis
    • severe ARDS has the worst mortality (45%) compared to mild and moderate
Presentation
  • Symptoms
    • dyspnea
  • Physical exam
    • tachypnea
    • tachycardia
    • diffuse crackles
Studies
  • Making the diagnosis
    • based on Berlin definition
Imaging
  • Chest radiography
    • indication
      • initial imaging study in the workup of ARDS
Differential
  • Diffuse alveolar hemorrhage
    • differentiating factor
      • in addition to acute respiratory failure, patients also have an unexplained drop in their hemoglobin concentration
  • Vaping-associated lung disease 
    • ground-glass opacities on imaging that can progress to ARDS
Treatment
  • Approach to treatment
    • the goal is to maintain gas exchange while avoiding ventilator-induced lung injury
  • Interventional
    • mechanical ventilation 
      • indication
        • to maintain adequate gas exchange while minimizing lung injury
          • low tidal volume
          • low plateau pressures
          • titrating up positive end-expiratory pressure (PEEP)
            • PEEP protects against atelectrauma 
      • settings
        • initial tidal volume to 8 mL/kg and reduce gradually to 6 mL/kg (low tidal volumes)  
          • want to achieve an inspiratory plateau airway pressure ≤ 30 cm H2O
        • titrate PEEP to prevent tidal alveolar collapse 
        • initial respiratory rate to approximate baseline minute ventilation (≤ 35/min)
        • oxygenation goal is a PaO2 of 55-80 mmHg
        • pH goal is 7.30-7.45
Complications
  • Nosocomial pneumonia
  • Pneumothorax
  • Chronic respiratory failure

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