Sickle Cell Acute Chest Syndrome

Acute chest syndrome (ACS) is a new pulmonary infiltrate with fever, respiratory symptoms or hypoxia in sickle cell disease, and is a leading cause of death.

• Occurs in about 50% of patients at least once; peak age 2 to 4 years in children, more severe in adults.
• Causes: infection (Chlamydia, Mycoplasma, viruses, pneumococcus), fat embolism from infarcted marrow, pulmonary infarction, hypoventilation from rib/chest pain and opioids, atelectasis.
• Complications: respiratory failure, stroke, multiorgan failure, pulmonary hypertension, chronic lung disease; mortality 3% in adults.

• Fever, cough, chest pain, dyspnoea, wheeze, hypoxia, often 2 to 3 days after onset of a pain crisis or surgery.
• Tachypnoea, crackles, bronchial breathing, effusion.
• Rapid deterioration, confusion.

• Chest radiograph: new infiltrate (lobar or multilobar), repeated daily.
• Oximetry, arterial blood gas, full blood count (fall in haemoglobin and platelets, leucocytosis), reticulocytes, LDH, CRP, group and cross match.
• Blood cultures, atypical pathogen testing (PCR, urine antigens), sputum.
• CT pulmonary angiography for suspected embolism, echocardiography for pulmonary hypertension.
• Bronchoscopy rarely (fat laden macrophages).

• Oxygen to keep saturation above 95%, incentive spirometry hourly, cautious hydration (avoid overload, 1 to 1.5 times maintenance).
• Antibiotics: ceftriaxone 1 to 2 g daily plus azithromycin 500 mg daily (or macrolide/doxycycline) for 7 days.
• Analgesia: avoid hypoventilation, use multimodal agents with regional blocks; bronchodilators (salbutamol 2.5 to 5 mg nebulised) for wheeze.
• Transfusion: simple transfusion to raise haemoglobin to 10 g/dL for hypoxia or falling haemoglobin; exchange transfusion for severe ACS (PaO2/FiO2 under 200, progressive disease, neurological signs), targeting HbS under 30%.
• Corticosteroids are controversial (rebound pain, readmission); use dexamethasone 0.3 mg/kg only in selected severe cases.
• Respiratory support: high flow oxygen, CPAP, ventilation, ECMO in refractory cases; inhaled nitric oxide.
• Thromboprophylaxis; avoid overhydration; hydroxyurea 15 to 35 mg/kg daily for prevention of recurrence (reduces ACS by 50%).
• Chronic transfusion for recurrent episodes despite hydroxyurea; vaccinations, penicillin prophylaxis in children.