Definition of Acute Chest Syndrome in Sickle Cell Disease
Acute chest syndrome (ACS) is defined as a new segmental infiltrate on chest radiograph accompanied by lower respiratory tract symptoms, chest pain, and/or hypoxemia in a patient with sickle cell disease. 1
Diagnostic Criteria
The diagnosis requires both radiographic and clinical findings 1:
Radiographic Component
- New pulmonary infiltrate visible on chest imaging (chest radiograph is the gold standard imaging modality) 2
Clinical Component (Any One of the Following)
- Fever > 38.5°C (101.3°F) 2
- Cough 2
- Wheezing 2
- Hypoxemia (PaO2 < 60 mm Hg) 2
- Tachypnea 2
- Chest pain 2
- Dyspnea 3
- Shortness of breath 3
Clinical Significance and Epidemiology
ACS is the leading cause of death in sickle cell disease, with up to 13% all-cause mortality. 4, 2 This makes it a cannot-miss diagnosis requiring immediate recognition and aggressive management 2.
- Occurs in approximately 50% of patients with sickle cell disease during their lifetime 2
- Most common in children aged 2-4 years 2
- Up to 80% of patients with prior ACS will experience recurrence 2
- Accounts for 25% of all deaths in sickle cell disease 5
Pathophysiology
The underlying mechanism involves vaso-occlusion in pulmonary vessels resulting in hypoxia, release of inflammatory mediators, acidosis, and infarction of lung tissue 2.
Common Precipitating Factors
- Infection (viral or bacterial) - most common cause 2, 6
- Rib infarction 2
- Pulmonary fat embolism - particularly in severe cases and adults 2, 6
- Hypoventilation related to inadequately treated thoraco-abdominal pain 1
- Reduced inspiratory effort following general anesthesia 1
A specific cause is identified in 38% of all episodes and 70% of episodes with complete diagnostic workup. 6
Clinical Presentation Patterns
Initial Presentation
Nearly half of patients are initially admitted for another reason, mainly pain crisis, and subsequently develop ACS during hospitalization. 6 This highlights the importance of vigilant monitoring in all hospitalized sickle cell patients.
Common Presenting Symptoms
Disease Progression
- Hypoxia with decreasing hemoglobin values 6
- Progressive multilobar pneumonia 6
- Can progress to respiratory failure requiring mechanical ventilation in 20% of adult patients 3
Age-Related Differences
Patients who are 20 or more years of age have a more severe course than younger patients. 6
- Children: Milder disease that is often infectious in etiology 7
- Adults: More severe disease with pulmonary fat embolism frequently a component 7
Critical Pitfall to Avoid
ACS can develop acutely or after initial presentation for a pain event, with or without fever. 1 Do not assume that patients admitted for uncomplicated pain crisis are safe from developing ACS—maintain high clinical suspicion and implement preventive measures (incentive spirometry every 2 hours) for all admitted patients with chest or back pain 4.