Acute Chest Syndrome (Sickle Cell)

🔥 Acute Chest Syndrome (ACS) is the leading cause of death in sickle cell disease (SCD) – up to 25% of SCD mortality. Often follows vaso-occlusive crisis (VOC) with severe bone/chest pain → rapid respiratory failure. 🚨 Urgent haematology consult + consider HDU/ICU early. Early exchange transfusion saves lives.

🩺 Definition & Epidemiology

• Diagnostic criteria (Vichinsky/NHLBI standard): New pulmonary infiltrate on CXR/CT involving ≥1 lung segment (not atelectasis) PLUS ≥1 of:
  • Chest pain
  • Fever ≥38.5°C
  • Respiratory symptoms/signs (cough, tachypnoea >20/min, increased work of breathing, wheeze, rales)
  • Hypoxaemia (SpO₂ drop ≥3% from baseline or <94% on air; PaO₂ <60 mmHg)
• Occurs in ~50% lifetime risk in HbSS/HbSβ⁰ thalassaemia; less in HbSC/HbSβ⁺.
• Peak age: children 2–4 y; adults also affected; recurrence risk high (up to 80% after first episode).

⚡ Triggers / Pathophysiology

• Infection (commonest: viral/bacterial pneumonia, e.g., pneumococcus, mycoplasma, Chlamydia, RSV, influenza)
• Fat embolism from infarcted bone marrow (rib/sternum/vertebrae → necrotic fat → pulmonary emboli)
• Pulmonary vaso-occlusion/infarction (sickled cells occlude lung vessels → ischaemia)
• Other: hypoventilation from pain/opioids, aspiration, surgery/anaesthesia

📊 Clinical Features & Red Flags

• New/severe chest/rib/back pain (often during VOC)
• Fever, cough, dyspnoea, tachypnoea, hypoxia (falling SpO₂), increased work of breathing
• Bilateral basal crepitations, wheeze (if reactive airways)
• Falling Hb (from baseline), reticulocytosis/leukocytosis
• Red flags: rapid progression, multilobar infiltrates, severe hypoxia, respiratory distress → ICU transfer

🧪 Investigations

• FBC + reticulocytes: Anaemia (falling Hb), leukocytosis, ↑ reticulocytes
• CXR (urgent): New infiltrates (often bilateral lower lobes; hallmark)
• Bloods: CRP/ESR, LFTs (↑ bilirubin), blood cultures, ABG if SpO₂ <94%
• Microbiology: Respiratory viral panel/PCR (influenza, RSV), sputum/blood cultures
• Other: Hb electrophoresis (confirms SCD genotype), consider CT chest if unclear

🛠️ Management (Aggressive & Multidisciplinary)

• ABC + monitoring: Oxygen to keep SpO₂ >94% (or baseline); consider HFNC/CPAP/BiPAP/non-invasive → intubation if failing.
• Pain control: Aggressive multimodal analgesia (opioids IV PCA, paracetamol, NSAIDs if no contraindication) to reduce splinting/hypoventilation.
• Incentive spirometry: Every 1–2 h while awake (prevents atelectasis; strong evidence).
• Antibiotics: Broad-spectrum IV (cover pneumococcus + atypicals): e.g., ceftriaxone + azithromycin/macrolide; add vancomycin if MRSA risk.
• Transfusion:
  • Simple transfusion if Hb >1 g/dL below baseline & symptomatic (target Hb 10 g/dL max to avoid viscosity).
  • Exchange transfusion (preferred in severe/progressive cases): aim HbS <30% (urgent if rapid deterioration, multilobar, hypoxia despite O₂, respiratory failure).
• Fluids: Euvolemia (avoid overload → pulmonary oedema); maintenance IV if NPO.
• Other: Bronchodilators if wheeze; VTE prophylaxis (heparin if no contraindication); consult haematology/PICU early.

Prevention

• Hydroxyurea (increases HbF, reduces VOC/ACS episodes; start early in HbSS).
• Regular transfusions if recurrent ACS (keep HbS <30%).
• Immunisations (pneumococcal, influenza, COVID-19), penicillin prophylaxis.
• Avoid triggers (dehydration, hypoxia, infection).

Clinical Pearl (Exam/OSCE/MCQ): Any SCD patient with new chest pain + fever/respiratory symptoms + new CXR infiltrate = ACS until proven otherwise Early recognition + exchange transfusion (if severe) is life-saving. Differentials: pneumonia, PE, fat embolism, aspiration – but treat as ACS first.

📚 Key References (2025–2026)

• UpToDate: Acute Chest Syndrome in SCD (updated Jan 2026)
• NHLBI Evidence-Based Management of SCD (2014, still core; ongoing updates)
• ASH Guidelines (cardiopulmonary complications, 2019/2020)
• Children's Hospital pathways (CHOP, CHoA, CHOC – 2025 revisions)
• British Journal of Haematology (2015 guideline, widely cited)