- Epidemiology & Risk Factors
- Exclusively occurs in pts with Sickle Cell Disease (SCD). Leading cause of death in SCD.
- Triggers: Infection (most common; esp. Mycoplasma, Chlamydia, Streptococcus pneumoniae, viruses), asthma exacerbation, vaso-occlusive crisis (VOC) of ribs/sternum causing hypoventilation/splinting, fat embolism from bone marrow necrosis.
- Pathogens (e.g., Chlamydia, Mycoplasma) cause inflammation → upregulates endothelial adhesion molecules → increases RBC/WBC sequestration in lungs. c
- Often presents 48-72 hours after admission for a painful VOC.
- Clinical Features
- Fever (>38.5°C).
- Chest pain, shortness of breath, tachypnea, cough, wheezing.
- Hypoxia/hypoxemia.
- PE: Crackles, decreased breath sounds.
- Diagnosis
- Initial/Diagnostic Criteria: CXR demonstrating a new radiodense pulmonary infiltrate involving at least one complete lung segment, plus ≥ 1 new symptom (fever, hypoxia, tachypnea, chest pain).
- Key Labs:
- CBC w/ diff (drop in Hb, leukocytosis).
- Blood and sputum cultures.
- ABG (hypoxemia).
- Blood type and crossmatch (crucial for potential transfusion).
- Imaging: CXR. Consider CT chest if PE strongly suspected or CXR equivocal.
- Differential Diagnostics
- Pneumonia: Often the trigger for ACS, making differentiation difficult. Treat for both simultaneously.
- Pulmonary Embolism (PE): Diff by lack of fever (usually) and classically clear CXR early in the course. CTPA if high clinical suspicion.
- Vaso-occlusive Crisis (Rib/Sternum): Diff by clear CXR. Note: Rib VOC causes splinting/atelectasis, which rapidly progresses to ACS.
- Asthma Exacerbation: Diff by diffuse wheezing without focal consolidations on CXR, though asthma can trigger ACS.
- Management
- Supportive (First-line):
- O2 Therapy: Target SpO2 >92%.
- Analgesics: IV opiates for pain (careful to avoid excessive sedation → hypoventilation).
- IVF: Euvolemia is the goal. Avoid fluid overload, which can precipitate pulmonary edema and worsen ACS.
- Medical Therapy:
- Empiric Broad-Spectrum Abx: Cephalosporin (e.g., Ceftriaxone) + Macrolide (e.g., Azithromycin) to cover typical and atypical organisms. c
- Incentive Spirometry: Mandatory to prevent atelectasis and further sickling.
- Bronchodilators: If concurrent wheezing or history of asthma.
- Transfusion (Target Hb ≈ 10 g/dL):
- Simple PRBC Transfusion: For early/mild ACS, symptomatic anemia, or Hb dropping >1 g/dL from baseline.
- Exchange Transfusion: For severe ACS (multilobar infiltrates, rapidly progressive disease, severe hypoxia/ARDS, or failure of simple transfusion). Rapidly reduces HbS % without increasing blood viscosity.
- Complications
- Acute Respiratory Distress Syndrome (ARDS) / Respiratory failure.
- Chronic lung disease / Pulmonary hypertension (Cor pulmonale).
- Neurologic complications (seizures, altered mental status) due to severe hypoxia.
- Death.