Acute Chest Syndrome

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

• Occurs in about 50% of patients at least once, often after vaso-occlusive pain crisis.

• Causes: infection (Chlamydia, Mycoplasma, viruses, S. pneumoniae), fat embolism from infarcted marrow, pulmonary infarction, hypoventilation from rib pain or opioids, atelectasis, fluid overload.

• Higher risk with HbSS, high white count, asthma, previous episodes.

• Complications: respiratory failure, stroke, multi-organ failure, chronic lung disease, mortality 3%.

• Fever, cough, chest pain, dyspnoea, hypoxia, tachypnoea, wheeze.

• Often develops 24 to 72 hours after admission for pain.

• Falling haemoglobin and platelets signal severe disease.

• Neurological signs from fat embolism.

• Chest radiograph: new infiltrate involving at least one lung segment (may lag clinical findings; repeat at 24 hours).

• Oxygen saturation (fall of 3% or below 92%), blood gas, full blood count, reticulocytes, blood cultures, respiratory viral PCR, Mycoplasma PCR, sputum.

• Ultrasound/CT pulmonary angiography for pulmonary embolism when suspected.

• Monitoring: continuous pulse oximetry, ICU level care if deteriorating.

• Oxygen to saturation above 95%, incentive spirometry hourly, analgesia without oversedation (morphine or hydromorphone with monitoring, regional blocks).

• Empirical antibiotics: ceftriaxone 1 to 2 g daily plus azithromycin 500 mg then 250 mg daily (or doxycycline 100 mg twice daily); oseltamivir 75 mg twice daily in influenza season.

• Fluids at maintenance only (avoid over hydration).

• Bronchodilators (salbutamol) if wheeze; corticosteroids only for asthma (rebound pain risk).

• Transfusion: simple transfusion for haemoglobin under 9 g/dL with hypoxia; exchange transfusion (target HbS under 30% and haemoglobin about 10 g/dL) for severe or progressive disease, rapid decline in saturation, multi-lobar involvement.

• Ventilation: non invasive pressure support or intubation with lung protective strategy; ECMO rescue.

• Prevention: hydroxyurea 15 to 35 mg/kg/day, chronic transfusion in recurrent disease, crizanlizumab or L-glutamine, early incentive spirometry in admitted patients.