Diagnostic Approach to Acute Chest Syndrome
Acute chest syndrome (ACS) in sickle cell disease is diagnosed by the presence of a new pulmonary infiltrate on chest radiograph combined with at least one of the following: fever >38.5°C, cough, wheezing, hypoxemia (PaO2 <60 mmHg), tachypnea, or chest pain. 1, 2
Clinical Presentation and Recognition
ACS commonly develops in patients initially admitted for vaso-occlusive pain crisis—nearly half of ACS episodes occur in patients hospitalized for another reason, predominantly pain. 3 Maintain high clinical suspicion as pain episodes frequently serve as a prodrome to ACS development. 4
Key presenting symptoms include:
- Fever and/or respiratory symptoms (dyspnea, cough, wheezing) 1, 4
- Chest pain (often pleuritic) 1, 2
- Hypoxemia with declining oxygen saturation 3, 2
- Progressive decline in hemoglobin values 3
- Tachypnea 1, 2
Diagnostic Workup
Imaging:
- Chest radiograph is the gold standard imaging modality and must demonstrate a new pulmonary infiltrate for diagnosis 1
- Progressive multilobar pneumonia is common 3
Laboratory Studies:
- Complete blood count (declining hemoglobin is characteristic) 1, 3
- Comprehensive metabolic panel 1
- Blood cultures before antibiotic administration 1
- Arterial blood gas or pulse oximetry to document hypoxemia 1, 2
- Consider procalcitonin for infection assessment 1
Additional Testing:
- Electrocardiogram to exclude acute coronary syndrome 1
- Respiratory secretion samples for culture and pathogen identification 3
Etiology Identification
A specific cause is identified in 38% of all episodes and 70% when complete diagnostic evaluation is performed. 3 The most common precipitants are:
- Infection (most common in children): Bacterial or viral pathogens, particularly community-acquired pneumonia 3, 4, 2
- Pulmonary fat embolism 3, 4
- Rib/bone infarction 1, 4
- Vaso-occlusive crisis 5
- Asthma exacerbation 5
Severity Assessment
Severe hypoxemia is the most useful predictor of severity and outcome. 2 Approximately 13% of patients require mechanical ventilation, with 3% mortality. 3
High-risk features indicating potential respiratory failure:
- Age ≥20 years (more severe course) 3
- Neurologic symptoms (46% develop respiratory failure) 3
- Progressive multilobar involvement 3
- Marked hypoxemia 2
Critical Pitfalls
Do not delay diagnosis waiting for fever—respiratory symptoms with new infiltrate are sufficient even without fever. 1, 2 Approximately 80% of patients with prior ACS will experience recurrence, making historical context essential. 1 Opiate-induced hypoventilation can trigger ACS, so analgesics must be administered judiciously despite the need for pain control. 2