- 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)
- 2 most common pathogens are atypical pneumonia pathogens
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.
- Important to identify the presence of infiltrate
- 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
- Opioids are the mainstay for pain control
- Fluids
- Administer d5 ½ ns fluid infusion to maintain euvolemia
- Monitor closely to avoid fluid overload
- Administer d5 ½ ns fluid infusion to maintain euvolemia
- 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
- reserved for severe crises
- Simple transfusion
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)
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