ARDS

Acute Respiratory Distress Syndrome (ARDS) – Judd Heideman

Background 

  • A syndrome of diffuse inflammation and injury of the alveoli and capillary endothelium leading to fluid and protein accumulation in the interstitium and alveoli, pulmonary edema, and hypoxemic respiratory failure; 30-50% mortality rate
  • Triggers:
    • Pulmonary 
      • Pneumonia (viral and bacterial)
      • Aspiration
      • Direct inhalation injury
      • Primary graft dysfunction of pulmonary transplant
      • Lung contusion
    • Extra-pulmonary
      • ​​​​​Sepsis (most common cause)
      • Trauma
      • Pancreatitis
      • Massive blood transfusions/TRALI
      • Burns
      • HSCT
      • Drugs (amiodarone, chemotherapy, cocaine, opioids)

Evaluation

  • Diagnosis: Berlin Criteria
    • New or worsening respiratory symptoms beginning within one week of diagnosis
    • New bilateral opacities present on chest radiograph or CT chest
      • Not explained by effusions, collapse of lobe/lung, or nodules
    • Absence of left heart failure or volume overload
  • Severity: based on PaO2/FiO2 ratio with a PEEP ≥ 5 cm H2O
    • PaO2 = arterial partial pressure of O2 (requires ABG)
    • FiO2 = fraction of inspired oxygen (expressed as a decimal between 0.21 and 1.0)

 

 

PaO2/FiO2 ratio

PEEP

Mild

201-300

≥5

Moderate

101-200

≥5

Severe

<100

≥5

 

Management

  • Frequently requires intubation; non-invasive ventilation not a great treatment
  • Low tidal volume (Vt) ventilation
    • Goal Vt = 4-8 mL/kg of predicted body weight (obese pts don’t have bigger lungs)
    • Predicted body weight is based on height and gender of pt
        • Males = 50 + 2.3 (height in inches – 60)
        • Females = 45.5 + 2.3 (height in inches – 60)
  • Plateau pressure goal: ≤30 cm H2O
  • Oxygenation goal: PaO2 55-80 or SpO2 88-95%
  • pH goal: ≥7.20, “permissive hypercapnia”
  • Treat the underlying cause (see “Triggers” above)
  • See below for further management of refractory hypoxemia

 

At VUMC:

  • To find FiO2, go to Summary tab > Flowsheet, look under “Resp support”
  • To order ABGs, search “resp care” and click on “Adult Respiratory Lab Panel (aka Respiratory care)” > arterial blood gas labs > Blood gas arterial
    • RT labs performed much faster in the MICU than on the floor
    • Consider A-line if checking 2 or more times/day