September 30, 2020

REBEL Core Cast 41.0 – Acute Chest Syndrome

Take Home Points

  • 100k people in US have sickle cell, the majority will at some point develop acute chest syndrome (ACS)
  • The mortality rate per episode is 3-9%, similar to those of STEMI
  • ACS is a syndrome – CXR infiltrate + respiratory symptoms
  • Treat it aggressively and early (antibiotics, respiratory support)
  • If you’re considering exchange transfusion – get hematology onboard quickly

REBEL Core Cast 41.0 – Acute Chest Syndrome

Sickle Cell Disease

  • A genetic RBC disorder affecting approximately 250 million people world wide
  • Affects approximately 100k people in the United States
  • 1 in 13 African Americans carry the sickle cell gene 

Pathophysiology 

  • Characterized as having one abnormal hemoglobin, hemoglobin S
  • Hemoglobin is made of iron (heme) and protein chains (globin)
    • Four types of globin molecule chains (alpha, beta, gamma, and delta)
    • HbSS, the hemoglobin of sickle cell anemia, consists of a pair of alpha chains and a pair of sickle beta chains
  • Normal RBC are donut-shaped and flexible, fit through arterioles and capillaries 
  • RBC with hemoglobin S are stiff and sickle-shaped
    • Distortion of RBC leads to destruction -> increased viscosity -> microvascular obstruction -> obstruction worsens hypoxia and acidemia worsens sickling
  • Initially, the sickling process is reversible when HbS is reoxygenated but with repeated episodes, the red cell membrane is permanently damaged
    • Anywhere from 5% to 50% of the circulating erythrocytes in a patient with SCD can be irreversibly sickled cells.
  • The overall effect is chronic, ongoing hemolysis and episodic periods of vascular occlusion, resulting in tissue ischemia affecting many organ systems.

Acute Chest Syndrome

  • Occurs into the majority of patients with sickle cell anemia at some point in their lives
  • Defined as new infiltrate on chest imaging + one other sign
    • Fever (101.3), cough,  wheezing, tachypnea, or chest pain
    • The definition is fairly broad – pneumonia easily falls in this category, treat both aggressively
  • Acute chest syndrome is the leading cause of death among people with sickle cell disease.
  • The mortality of a single episode is estimated at ~3-9%. This is equivalent to the mortality rate of patients with STEMI.

Precipitating Etiologies 

  • ACS has multiple potential inciting etiologies
    • Pulmonary infection, pulmonary infarction, fat emboli, rib infarction, dehydration, infection, inflammation, acidosis and stasis of blood (decreased cardiac output). 
    • Hypoxia is the strongest stimulus for sickling 
  • Iatrogenic causes 
    • Opioids leading to hypoventilation potential cause of ACS
  • 30% of ACS admitted to hospital will have an infectious cause identified
    • 2 most common pathogens are atypical pneumonia pathogens
      • Chlamydia pneumoniae (in adults) 
      • Mycoplasma pneumoniae (in pediatric patients)

Presentation

  • Respiratory symptoms are usually present, including cough, shortness of breath, chest pain, and fever
  • Rales are the most common physical exam finding, found anywhere between 48 – 70%
  • Potential differentials to consider
    • Myocardial infarction.
    • Decompensated chronic cor pulmonale.
    • Pulmonary embolism.
    • Splenic sequestration crisis 
    • Line infection (among patients with chronic indwelling lines or ports).

Ancillary Tests

  • CXR
    • Important to identify the presence of infiltrate
      • Keep in mind that imaging findings lag behind the presentation.
  • Bedside US
    • One study showed lung US to be more sensitive than CXR for ACS
    • Findings include B-lines and pleural effusion – keep in mind not specific to ACS
  • Complete blood count
  • Hemoglobin electrophoresis to determine % Hemoglobin S
  • Blood for type & screen.
  • Coagulation factors (INR, PTT, fibrinogen)
  • Electrolytes, including calcium level (ionized calcium level if available)
  • Liver function tests

Management

  • Oxygen
    • Given oxygen in order to keep saturations >92%
    • British guidelines recommend >95% or within 3% of patients baseline
  • Respiratory support
    • Bipap or HFNC – need to prevent atelectasis 
    • Incentive spirometer / early ambulation 
      • Incentive spirometry has been shown to prevent chest syndrome among patients admitted with painful vaso-occlusive crises.
  • Analgesia 
    • Opioids are the mainstay for pain control
      • Beware of oversedation and hypoventilation 
  • Fluids
    • Administer d5 ½ ns fluid infusion to maintain euvolemia
      • Monitor closely to avoid fluid overload
  • Systemic corticosteroids
    • Controversial – may prevent deterioration and need for transfusion but associated with higher rates of admission 
  • Antibiotics
    • Recommended regardless of cultures
    • Empiric broad-spectrum covering community-acquired pneumonia
      • Cephalosporin  / Macrolide to cover for Mycoplasma and Chlamydia
  • Transfusion
    • Simple transfusion
      • Mildly anemic (<7) and not severely ill
      • Severely anemic (<5) and severely ill
      • The consensus in the literature  is a goal of 10-11 mg/dL
      • Transfusion to >11 mg/dL could potentially increase blood viscosity, which may cause clinical hyperviscosity syndrome
    • Exchange transfusion (allows for rapid decrease in sickle cells without increasing viscosity)
      • reserved for severe crises 
        • partial pressure of arterial oxygen to <60 mm Hg (<8 kPa) 
        • presence of neurologic abnormalities or multiorgan failure
        • Rapidly progressive lung involvement
        • Patients with high risk for adverse outcomes, those that are pregnant or have multiple comorbidities
      • If unsure consult with hematology for recommendations
      • Contradictions
        • Severe anemia (<6), recommend first simple transfusion followed by exchange transfusion
        • Severe hypocalecemia 

Disposition 

  • All patients with ACS should be admitted to a monitored setting
  • Not all require ICU, however those with increasing age and comorbidities most likely to have poor outcomes.

Take-Home Points

  • 100k people in US have sickle cell, the majority will at some point develop ACS
  • The mortality rate per episode is 3-9%, similar to those of STEMI
  • ACS is a syndrome – CXR infiltrate + respiratory symptoms
  • Treat it aggressively and early (antibiotics, respiratory support) 
  • If you’re considering exchange transfusion – get hematology onboard quickly

Resources

Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie)

Cite this article as: Anand Swaminathan, "REBEL Core Cast 41.0 – Acute Chest Syndrome", REBEL EM blog, September 30, 2020. Available at: https://rebelem.com/rebel-core-cast-41-0-acute-chest-syndrome/.
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Anand Swaminathan

Clinical Assistant Professor of Emergency Medicine at St. Joe's Regional Medical Center (Paterson, NJ)
REBEL EM Associate Editor and Author

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