ARDS (Acute respiratory distress syndrome)

21 Mar

RAGING HYPOTHETICAL:

31 year old woman comes in from home with acute difficulty breathing.

 

She has a remote history of pneumonia and resulting respiratory failure requiring intubation. She denies recent viral illness, fever, trauma, or inhalational injury. She has no history of heart failure.
 
On exam she is tripod-ing and working hard to breathe. No rales are heard but she is taking shallow breaths at a rate of 60 per minute.
No signs of trauma to chest, normal pharyngeal exam, no stridor. Cardiac exam normal, blood pressure and heart rate within normal limits.
 
CXR reveals…
 
(patchy bilateral infiltrates without evidence of effusion)
ABG reveals normal pH and normal CO2 and PaO2 of 200 while on non-rebreather
 
Pro tip:
  • if a patient is on non-rebreather (FiO2 = 100%), their blood gas PaO2 is equal to their PaO2/FiO2 ratio.
  • If this number (PaO2) is less than 300 think about ARDS/ALI
 
Key Points:
 
ARDS is associated with significant mortality (up to 45%)
 
Risk factors for ARDS: 
  • Pulmonary infection
  • Sepsis
  • Inhalational injury (smoke)
  • Shock
  • Trauma (lung contusion)
  • Aspiration event
 
Diagnosis of ARDS (via AECC consensus in 1994):
  • Bilateral infiltrates on CXR
  • Absence of clinical signs of CHF
  • Marked Hypoxemia
  • PaO2/FiO2 ratio <300 for Acute lung injury or <200 for ARDS
  • Pulmonary Capillary Occlusion Pressure <18 (unlikely to be useful in ER setting)
 
Management:
  • Intubation to prevent and/or treat impending hypoxemic respiratory failure
  • Low tidal volume (6-8 ml/kg) to minimize further lung injury
  • Increasing PEEP may be useful in the ER to help maintain adequate oxygenation. Increased PEEP may also help stabilize lung volume and prevent further lung injury longer term, but this is not entirely clear.
  • Prone positioning – not something I would necessarily do in the ER but may be worth thinking about if the patient remains hypoxemic despite other efforts.  Call a pulmonologist.
Other things that are out there for refractory hypoxemia:
  • pharmacologic paralysis,
  • oscillating vent,
  • ECMO
Submitted by L. Cunningham. 
——————————————————————————————
References: Michael Donahoe. Acute respiratory distress syndrome: A clinical review. Pulm Circ. 2011 Apr-Jun; 1(2): 192–211. PMC3198645; image
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