• ARDS is a life-threatening inflammatory condition of the lungs.
• Globally it affects 3 million patients annually and 10% of all ICU admissions.
• Triad of hypoxia, bilateral CXR opacities, and reduced lung compliance.

Pathophysiology

• Three phases: exudative, proliferative and fibrotic.
• Acute exudative phase = lungs initial response to injury and is characterized by the innate. inflammatory damage of alveolar endothelial and epithelial barriers allowing for the accumulation of fluid within the interstitium and alveolus.
• Direct insults or indirect lung injury from systemic critical illness (Table 1).

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• The Berlin Definition (Table 2) is the most widely used clinical criteria.
• Consider common mimics of ARDS:
  • Congestive Heart Failure
  • Idiopathic pulmonary fibrosis
  • Diffuse alveolar hemorrhage
  • Drug-induced lung diseases
  • Cancer

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• Supportive therapy is mainstay.
• Identification and treatment of the underlying cause.
• High flow nasal canula is preferential for management of mild ARDS. However, non-invasive positive pressure ventilation can also be used in some circumstances.
• For more severe cases, ventilatory support with mechanical ventilation continues to be the hallmark of ARDS management.
• Lung protective ventilation and the avoidance of ventilator-induced lung injury (VILI) are important principles in mechanical ventilation of patients with ARDS.
• Initial ventilator settings:
  • Initial tidal volume (Vt): 6-8 mL/kg (ideal body weight)
  • Target Plateau Pressure ≤ 30 cmH2O
  • Permissive hypercapnia allowed to achieve above with goal pH ≥ 25
  • A PEEP of at least 5 cmH₂O should be used, and in more severe cases a higher PEEP should be used

• A more fluid restrictive resuscitation strategy is likely beneficial.
• Steroid use remains controversial. However, steroids should be used for COVID-19 related ARDS.
• For severe, refractory hypoxia related to ARDS:
  • Optimization of PEEP
  • Neuromuscular paralysis
  • Prone positioning
  • Institution of VV-ECMO

1. Thompson, T., Chambers, R. C., and Liu, K. D. 2017. Acute Respiratory Distress Syndrome. NEJM, 377(6), 562-572.

   
   

2. Fan, E., Brodie, D., Slutsky, A. S. 2018. Acute Respiratory Distress Syndrome: Advances in Diagnosis and Treatment. JAMA, 319(7), 698-710. 

   
   

3. Brower R.G. et al with The Acute Respiratory Distress Syndrome Network (ARDSnet). 2000. Ventilation With Lower Tidal Volumes as Compared With Traditional Tidal Volumes For Acute Lung Injury and The Acute Respiratory Distress Syndrome. NEJM, 342(18), 1301-1308.  

   
   

4. Wiedemann, H. P. et al with The National Heart, Lung, and Blood Institute and Acute Respiratory Distress Syndrome (ARDS) Clinical Trials Network. 2006. Comparison of Two Fluid-Management Strategies in Acute Lung Injury (FACtt trial). NEJM, 354, 2564-2575. 

   
   

5. Horby, P. with The RECOVERY Collaborative Group. 2021. Dexamethasone in Hospitalized Patients with Covid-19. NEJM, 384:693-704. 

   
   

6. Frat J-P. et al. 2015. High-Flow Oxygen through Nasal Cannula in Acute Hypoxemic Respiratory Failure. NEJM, 372:2185-2196. 

   
   

7. Guerin et al. 2013. Prone Positioning in Severe Acute Respiratory Distress Syndrome. NEJM. 368: 2159-2168. 

   
   

8. EM Cases Podcast: EM Quick Hits 22 Postpartum Hemorrhage, Phenobarbital in Status Epilepticus, Managed Alcohol Programs, Traumatic Cardiac Arrest, Cholangitis, ED Approach to ARDS. Summarizing podcast with accompanying show notes.