Updated: 2/4/2021

Acute Respiratory Distress Syndrome (ARDS)

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Snapshot
  • A 46-year-old woman is admitted to the ICU with severe pancreatitis. During the first 24 hours of admission, severe hypoxemia that requires ventilatory support with high concentrations of inspired oxygen develop. On exam the patient has rhonchi and crackles bilaterally. An arterial blood gas collected at 60% FiO2 reveals pH 7.42, PCO2 35 mmHg, and PO2 108 mmHg.
Introduction
  • Defined as acute diffuse, inflammatory lung injury leading to increased vascular permeability, increased lung weight and loss of aerated lung tissue   
    • hyperactivation of coagulation and/or inflammation damages both type I and II pneumocytes
      • ↓ type II pneumocytes results in ↓ surfactant production
      • ↓ surfactant production results in low lung compliance and subsequent atelectasis
    • repair often results in interstitial fibrosis
  • Causes
    • infection
      • pneumonia
      • sepsis
        • typically gram-negative sepsis
    • aspiration
    • acute pancreatitis
    • trauma with shock
    • amniotic fluid embolism (rare)
    • uremia
Presentation
  • Symptoms
    • dyspnea
  • Physical exam
    • tachypnea
    • bilateral rales and decreased breath sounds
Evaluation
  • Arterial blood gas
    • severe hypoxemia on pulse oximetry and ABG
      • may not be responsive to 100% O2
      • atelectasis results in intrapulmonary shunting
  • Radiology
    • diffuse, bilateral alveolar infiltrates on CXR
    • ground glass opacities and consolidations on chest CT often with dependent lung predominence
  • Histology 
    • diffuse alveolar damage
    • protein-rich leakage (exudate) forming an intra-alveolar hyaline membrane 
  • Severity graded on PaO2 / FiO2 ratio and required PEEP (see below)
Treatment
  • Respiratory support & treat underlying cause
    • Mechanical ventilation with low tidal volume (4-6 mL/kg ideal body weight) 
    • High FiO2
    • PEEP (positive end-expiratory pressure) 
      • prevents airway collapse at end-expiration
      • recruits collapsed alveoli
        • increases FRC and decreases shunting
      • improves oxygenation 

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