15- ACUTE RESPIRATORY DISTRESS SYNDROME

• Acute Respiratory Distress Syndrome (ARDS)


  Type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs
• ARDS

  • New bilateral diffuse patchy or homogenous pulmonary infiltrates
  • Respiratory distress
  • Stiff lungs (↓ compliance, ↑ dead space)
  • Airflow limitation
  • Gas exchange abnormalities
  • Pleural effusions
• ARDS


  Early feature of generalized inflammatory response, may lead to multi-organ failure
• No cardiac cause (PCWP<18, normal echo)
• Causes of ARDS

  • Direct lung injury: Pneumonia, gastric aspiration, inhalation injury, vasculitis
  • Secondary to severe systemic illness: Shock, sepsis, hemorrhage, multiple transfusions, severe trauma, etc.
• Clinical features of ARDS

  • Shortness of breath
  • Cyanosis
  • Tachypnea (1st sign, followed by increasing hypoxemia & breathlessness)
  • Tachycardia
  • Peripheral vasodilatation
  • Bilateral fine inspiratory crackles
  • Noncardiogenic pulmonary edema (due to lung damage and release of inflammatory mediators→increased capillary permeability)
• Causes of death in ARDS

  • Multiorgan failure
  • Hemodynamic instability
• Investigations

  • CBC
  • U&E
  • LFT
  • amylase
  • clotting
  • CRP
  • blood cultures
  • ABG
• CXR

  Shows bilateral pulmonary infiltrates
• Pulmonary artery catheter

  Measures pulmonary capillary wedge pressure (PCWP), should be <18 (differentiates from cardiogenic pulmonary edema where PCWP is >18)
• Diagnostic criteria (all 4 must exist)

  • Acute onset
  • CXR: bilateral infiltrates
  • Pulmonary capillary wedge pressure (PCWP) <18mmHg or a lack of clinical congestive heart failure
  • Refractory hypoxemia with PaO2: FiO2 <200
• Berlin definition of ARDS severity

  • Mild (300-200)
  • Moderate (200-100)
  • Severe (<100)
  • Predicts mortality
• Management

  1. Admit to ICU

  2. Give supportive therapy

  3. Treat the underlying cause
• Sepsis management

  1. Identify organism(s)

  2. Treat accordingly
• Limit pulmonary edema

  1. Fluid restriction

  2. Diuretics

  3. If failed: hemofiltration
• Prognosis

  • Overall mortality is 50–75%
  • Worse prognosis if: Cause is secondary to systemic illness
  • Older age
  • Failing of other organs