What is acute chest syndrome?

Acute Chest Syndrome in Sickle Cell Disease

Acute chest syndrome (ACS) is a life-threatening complication of sickle cell disease characterized by a new segmental infiltrate on chest radiograph accompanied by lower respiratory tract symptoms, chest pain, and/or hypoxemia. 1, 2

Definition and Clinical Presentation

• ACS is a leading cause of death for patients with sickle cell disease, accounting for approximately 25% of all deaths 3
• Diagnostic criteria include a new infiltrate on pulmonary imaging combined with one or more of the following: fever, cough, wheezing, hypoxemia, tachypnea, or chest pain 4
• Patients typically present with respiratory symptoms including fever, cough, chest pain, and shortness of breath, which can progress to respiratory failure requiring mechanical ventilation in up to 20% of adult patients 5
• ACS can present acutely or develop after initial presentation for a pain event, with or without fever 1

Etiology and Pathophysiology

• Multiple causative factors may contribute to ACS development:
  • Infection (viral, bacterial, Mycoplasma, or Chlamydia) 1
  • Pulmonary infarction 1
  • Pulmonary fat embolism 1
  • Hypoventilation related to inadequately treated thoraco-abdominal pain 1
  • Reduced inspiratory effort, often following general anesthesia 1
• The pathophysiology involves vaso-occlusion in pulmonary vessels resulting in hypoxia, release of inflammatory mediators, acidosis, and infarction of lung tissue 4
• Children with sickle cell disease and reactive airway disease have an increased incidence of ACS 1

Initial Assessment and Management

• Emergency transfer to an acute care setting is essential for patients with sickle cell disease presenting with acute chest pain 1, 2
• Initial assessment should include:
  • Oxygen saturation monitoring 2
  • Complete blood count to establish baseline hemoglobin level 1
  • Chest radiograph (the gold standard for diagnosis) 4
  • Blood cultures if fever is present 2
• Lung ultrasound has demonstrated promise as an alternative imaging modality 5

Treatment Protocol

Respiratory Support

• Administer oxygen therapy to maintain SpO2 above baseline or 96% (whichever is higher) 2
• Implement incentive spirometry every 2 hours to prevent atelectasis and worsening of ACS 2, 5
• Consider continuous positive airway pressure, high-flow nasal oxygen, or nasopharyngeal airway for patients with increasing respiratory distress 2

Antimicrobial Therapy

• Initiate antibiotics if temperature reaches ≥38.0°C or if there are signs of sepsis 2
• Empiric antibiotics should cover atypical pathogens 5

Pain Management

• Provide aggressive pain control with parenteral opioids for moderate to severe pain 1, 2
• Use patient-controlled analgesia (PCA) with scheduled around-the-clock dosing rather than as-needed dosing 1, 2

Hydration

• Administer adequate hydration while carefully monitoring fluid balance to prevent overhydration 2
• Oral hydration is preferred when possible, but intravenous fluids should be used if oral intake is inadequate 2, 6

Blood Transfusion

• Simple or exchange transfusions are often necessary for severe cases 1, 5
• Transfusion decisions should be made in consultation with a hematologist, considering the risks of alloimmunization (7-30% of patients) 2
• Transfusion increases blood's oxygen-carrying capacity and reduces complications by reducing hemoglobin S percentage 3

Monitoring and Prevention of Complications

• Perform regular monitoring of oxygen saturation, as decreasing SpO2 provides early warning of worsening ACS 2
• Implement thromboprophylaxis for post-pubertal patients due to increased risk of deep vein thrombosis 2
• Encourage early mobilization when appropriate 2
• Provide chest physiotherapy if the patient is unable to mobilize 2

Indications for ICU Admission

• Consider ICU admission for:
  • Rapidly progressive disease despite initial interventions 2
  • Consideration of exchange transfusion 2
  • Respiratory failure requiring mechanical ventilation 5

Common Pitfalls and Caveats

• ACS can develop after initial presentation for pain crisis, requiring ongoing vigilance even in patients admitted for vaso-occlusive crisis 1, 7
• Avoid overhydration, which can lead to pulmonary edema 2
• Monitor for transfusion reactions in patients receiving blood products 2
• Although ACS is more common in those with homozygous SCD, clinicians should consider ACS in all SCD patients 5
• Despite increased understanding of its etiology and pathogenesis, ACS remains a leading cause of morbidity and mortality in SCD, requiring a high index of suspicion and aggressive management 7