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Acute Respiratory Distress Syndrome (ARDS)

JC Armstrong

Background

  • A syndrome of diffuse systemic inflammation which damages the alveoli/capillary endothelium interface causing fluid and protein accumulation within the interstitium and alveoli leading to impaired gas exchange, decreased lung compliance, and pulmonary hypertension.
  • ARDS new definition: Onset within 1 week of known insult with new/worsening respiratory status with bilateral opacities seen on CXR/CT or bedside US not fully explained by cardiac failure/volume overload with PaO2:FiO2 ≤ 300 or SpO2:FiO2 ≤ 315 with respiratory support of PEEP ≥ 5 or HFNC ≥ 30L.

Triggers:

  • Direct
    • Pneumonia (viral and bacterial)
    • Aspiration
    • Lung contusion d/t trauma
    • Direct inhalation injury
    • Primary Graft dysfunction of pulmonary transplant
  • Indirect
    • Non-pulmonary Sepsis (most common cause)
    • Massive Blood Transfusion/TRALI
    • Hematopoietic stem cell transplantation
    • Drugs (Opioids, TCAs, ASA, cocaine, amiodarone, chemotherapy, salicylates)
    • Pancreatitis
    • Burns
    • Radiation

Evaluation

  • Severity: Based on PaO2/FiO2 ratio with PEEP  5 cm H20
  • PaO2- arterial pressure of O2 (Obtained by ABG)
  • FiO2- Fraction of inspired oxygen (expressed as a decimal between 0.21 and 1.0)
PaO2/FiO2 ratio SpO2/FiO2 (if SpO2 ≤ 97%) if intubated PEEP or HFNC (Optiflow)
Mild 300-201 246-315 ≥5 or ≥30L
Moderate 200-101 149-245 ≥5 or ≥30L
Severe <100 <148 ≥5 or ≥30L

Management

  • Frequently requires intubation as non-invasive ventilation is not often effective.
  • Interventions with mortality benefit
    • Low tidal volume(Vt) ventilation (LTVV)
      • Goal Vt is 4-8 mL/kg of ideal body weight
      • Target plateau pressure of  30 cm H2O
      • Oxygenation goal: PaO2 55-80 mmHg or SpO2 88-95%
      • Slowly titrate PEEP and FiO2 concurrently to achieve oxygenation goals
      • pH goal: \(\ge\) 7.20; “permissive hypercapnia”
      • Treat ventilator dyssynchrony
    • Proning
      • Can be considered if moderate to severe ARDS and oxygenation does not improve with LTVV
      • Most recent study (PROSEVA) suggested mortality benefit to proning patients with moderate to severe ARDS
      • Not routinely done at VUMC
  • Interventions that probably won’t hurt the patient but with less data to support them
    • Conservative fluid management with IV diuresis as needed (at risk for pulmonary edema d/t vascular leak); goal of net even or negative. FACTT study demonstrated 2 more ventilator-free days with aggressive diuresis, but no mortality difference
    • Glucocorticoids in ARDS d/t septic shock, COVID, CAP, steroid-responsive conditions; may shorten time on ventilator but may also result in some neuromuscular weakness
  • American Thoracic Society Guidelines of 2024 placed emphasis on early ECMO involvement and neuromuscular blockade in severe ARDS patients. Two trials on neuromuscular blockade (ACURASYS and ROSE) with conflicting results. EOLIA suggest benefit to ECMO in patients with P/F<80 or hypercapnic respiratory acidosis.