Episode 195: ARDS

Show Notes

• Definition of ARDS:
  • Non-cardiogenic pulmonary edema characterized by acute respiratory failure.
  • Berlin criteria for diagnosis include acute onset within 7 days, bilateral pulmonary infiltrates on imaging, not fully explained by cardiac failure or fluid overload, and impaired oxygenation with PaO2/FiO2 ratio <300 mmHg, even with positive end-expiratory pressure (PEEP) >5 cm H2O.
• Severity based on oxygenation (Berlin criteria):
  • Mild: PaO2/FiO2 200-300 mmHg
  • Moderate: PaO2/FiO2 100-200 mmHg
  • Severe: PaO2/FiO2 <100 mmHg
• Epidemiology:
  • Occurs in up to 23% of mechanically ventilated patients.
  • Mortality rate of 30-40%, primarily due to multiorgan failure.
• Differentiation from Cardiogenic Pulmonary Edema:
  • Chest CT shows diffuse edema and pleural effusion in cardiogenic edema; patchy edema, dense consolidation in ARDS.
  • Ultrasound may show diffuse B lines in cardiogenic edema; patchy B lines and normal A lines in ARDS.
• Pathophysiology:
  • Exudative phase: Immune-mediated alveolar damage, pulmonary edema, cytokine release.
  • Proliferative phase: Reabsorption of edema fluid.
  • Fibrotic phase: Potential for prolonged ventilation.
• Etiology:
  • Direct lung injury (pneumonia, toxins, aspiration, trauma, drowning) and indirect causes (sepsis, pancreatitis, transfusion reactions, certain drugs).
• Diagnostics:
  • Comprehensive workup including imaging (chest X-ray, CT), laboratory tests (complete blood count, basic metabolic panel, blood gases), and specialized tests depending on suspected etiology.
• Management Strategies:
  • Steroids: Beneficial in certain etiologies of ARDS, with specifics on dosing and duration.
  • Fluid Management: Conservative fluid strategy, diuresis guided by patient condition.
  • Ventilation: Non-invasive ventilation (NIV) preferred in specific cases; mechanical ventilation strategies to ensure lung-protective ventilation.
  • Proning: Used in severe ARDS to improve oxygenation.
  • Inhaled Vasodilators: Used for refractory hypoxemia and specific complications like right heart failure.
  • Extracorporeal Membrane Oxygenation (ECMO): Considered for severe ARDS as salvage therapy.
  • Supportive Care: Includes monitoring and management of complications, nutrition, and physical therapy.
• Ventilation Specifics:
  • Tidal volume and pressure settings aim for lung-protective strategies to prevent ventilator-induced lung injury.
  • Permissive hypercapnia, plateau pressure, PEEP, and ventilation mode adjustments based on patient response.
  • ARDSnet Table: ventilator_protocol_2008-07