Acute Respiratory Distress Syndrome (ARDS)

Berlin Criteria Definition ₍₁₎

1. P_aO₂/F_iO₂ < 300 (0-100 = severe, 101-200 = moderate, 201-300 = mild) on PEEP of at least 5 mmHg.
2. Radiographic evidence of non-cardiogenic pulmonary edema (see picture below)
3. Acute onset within 1 week of known insult

Etiologies

• Sepsis
• Aspiration
• Pneumonia (including COVID-19 or influenza)
• Trauma
• Transfusion-Related Acute Lung Injury (TRALI)
• Stem cell transplantation
• Pancreatitis
• Drugs/Alcohol

Basic Management

• Ventilator settings
  • Tidal Volume: 6 mL/kg ideal body weight ₍₂₎
    • This may induce hypercapnea and respiratory acidosis, which is allowed to a limit of pH of 7.3
  • F_iO₂: Start at 100% and wean down as able
  • RR: Will have to start higher (~30 rpm) to compensate for low tidal volume to maintain an adequate minute ventilation volume (MVV = V_T x RR)
  • PEEP: Controversial, but the idea is to keep the stress index at 1 (keeping the pressure-time curve linear instead of convex or concave)
    • Concave (Stress index < 1) indicates pressure rising too quickly, consider increasing PEEP to help inflate lung
    • Convex (Stress index >1) indicates pressure rising too slowly, consider decreasing PEEP
• Diuresis
  • Attempts to diurese to a goal of CVP < 4 mmHg as long as patient remains well-perfused
• Paralyzation
  • Mechanism of benefit is unclear, but decreases mortality likely as a result of decreasing asynchrony on the ventilator ₍₃₎
• Proning
  • With the patient prone, gas will move in a dependent fashion toward the posterior lung fields, which carry a greater surface area, allowing for improved gas exchange.
  • Typically reserved for an S_pO₂/F_iO₂ ratio < 180 or P_aO₂/F_iO₂ ratio < 150
• ECMO (Extracorporeal Membrane Oxygenation)
  • Can be considered in individuals not improving with above therapies
• Inhaled Nitric Oxide not shown to have mortality benefit ₍₄₎
• Surfactant not shown to have mortality benefit ₍₅₎
• Steroids not shown to have mortality benefit ₍₆₎

References

1. Amin, Zulkifli, et al. “Benefit of the Application of New ARDS Criteria (Berlin) Compared to Old Criteria (AECC) in a Tertiary Hospital in a Developing Country.” Indian Journal of Public Health Research & Development, vol. 8, no. 2, 2017, p. 273., doi:10.5958/0976-5506.2017.00125.5.
2. Ventilation with Lower Tidal Volumes as Compared with Traditional Tidal Volumes for Acute Lung Injury and the Acute Respiratory Distress Syndrome. New England Journal of Medicine, 45(1), 19-20. doi:10.1097/00132586-200102000-00017
3. Mclean, D., & Eikermann, M. (2018). Neuromuscular Blockers in Early Acute Respiratory Distress Syndrome. 50 Studies Every Intensivist Should Know, 123-128. doi:10.1093/med/9780190467654.003.0020
4. Use of inhaled nitric oxide in patients with acute respiratory failure with low blood oxygen does not improve survival. (n.d.). Retrieved November 11, 2020, from https://www.cochrane.org/CD002787/EMERG_use-inhaled-nitric-oxide-patients-acute-respiratory-failure-low-blood-oxygen-does-not-improve
5. Raghavendran, K., Willson, D., & Notter, R. (2011, July). Surfactant therapy for acute lung injury and acute respiratory distress syndrome. Retrieved November 11, 2020, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3153076/
6. Khilnani, G., & Hadda, V. (n.d.). Corticosteroids and ARDS: A review of treatment and prevention evidence. Retrieved November 11, 2020, from http://europepmc.org/articles/PMC3109833