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Acute Respiratory Distress Syndrome (ARDS) | Clinical Medicine

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Science and Nature

Definition and Diagnosis of ARDS

  • Acute Hypoxemia: Develops within one week, indicated by:
    • SpO2 < 90% or PaO2 < 60 mmHg.
  • PF Ratio: The ratio of arterial oxygen partial pressure (PaO2) to the fraction of inspired oxygen (FiO2) must be < 300.
  • Imaging Findings: Diffuse bilateral infiltrates visible on chest X-ray or CT scan.
  • Exclusion of Cardiogenic Pulmonary Edema: Confirmed via Swan-Ganz catheter showing pulmonary capillary wedge pressure < 18 mmHg.

Pathophysiology

  • Diffuse Alveolar Damage (DAD): Injury to Type 1 and Type 2 alveolar cells leads to:
    • Fluid and protein accumulation in alveoli.
    • Decreased surfactant production, resulting in alveolar collapse.
  • Ventilation-Perfusion (V/Q) Mismatch: Poor ventilation with normal perfusion leads to significant hypoxemia.

Causes of ARDS

  • Direct Lung Injury:
    • Pneumonia (including SARS-CoV-2).
    • Aspiration of gastric contents.
    • Inhalation of toxic substances.
  • Indirect Lung Injury:
    • Systemic infections (sepsis).
    • Inflammatory conditions (e.g., pancreatitis).
    • Transfusion-related lung injury.

Complications

  • Pulmonary Hypertension: Due to hypoxic vasoconstriction, leading to increased pulmonary vascular resistance and potential right heart failure.
  • Ventilator-Associated Pneumonia (VAP): Risk increases with prolonged intubation.
  • Ventilator-Induced Lung Injury: Due to excessive airway pressures or volumes, leading to barotrauma or volutrauma.

Management and Treatment

  • Ventilation Strategies:
    • Low tidal volume ventilation (< 6 cc/kg).
    • Appropriate PEEP settings to prevent alveolar collapse.
  • Sedation and Neuromuscular Blockade: To synchronize patient breathing with the ventilator.
  • Proning: Improves ventilation and oxygenation in severe cases.
  • Extracorporeal Membrane Oxygenation (ECMO): Considered in refractory hypoxemia.

Diagnostic and Management Steps

  1. Confirm Acute Hypoxemia and PF Ratio < 300.
  2. Assess imaging for bilateral infiltrates.
  3. Rule out cardiogenic causes using echocardiogram or Swan-Ganz catheter.
  4. Initiate low tidal volume ventilation and monitor plateau pressures.
  5. Consider proning and ECMO for severe cases.

Researchers/Sources Featured

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