Acute chest syndrome

Background

Lobes of the lung with related anatomy.

Pulmonary arterial tree anatomy.

• The leading cause of death in patients with HbSS in the United States
  • HbSS individuals are at higher risk than HbSC, but acute chest may occur in both genotypes
• Occurs most commonly in the 2-4yr old age group and then declines with age
• Pathophysiology is due to deoxygenation of Hb, leading to sickling in the pulmonary vasculature, causing vaso-occlusionm, ischemia, and endothelial injury
  • In pediatric population, ACS is more often triggered by asthma or viral/bacterial pulmonary infection, leading to local hypoxia
  • In adult population, ACS is commonly associated with vaso-occlusive pain, which may lead to hypoventilation or long bone fat/marrow emboli
  • However, a specific cause is not identified in a majority of cases

Causes

• Pulmonary infection
  • Chlamydophila pneumoniae and Mycoplasma pneumoniae are most common organisms
  • May also be caused by S. aureus, H. influenzae, Klebsiella, and viruses
    • Infection due to S. pneumoniae is now rare due to pneumococcal immunization and prophylactic penicillin therapy
• Fat emboli
  • Suspect if symptoms start 2-3 days following acute pain crisis
  • Can cause microvasculature occlusion in the pulmonary circulation, leading to bone marrow infarction
  • Autopsies have shown bony slivers and marrow fat found in pulmonary vasculature of patients
• Rib infarction
• Overly aggressive IV hydration
• Vaso-occlusive pain crisis
• Asthma
• Iatrogenic
  • Opioid analgesics can lead to hypoventilation

Clinical Features

• New infiltrate on chest x-ray PLUS one of the following signs or symptoms
  • Fever >38.5°C (101.3°F)
  • Cough
  • Wheezing
  • Tachypnea
  • Chest pain
  • Hypoxemia

Complications

• Pulmonary Embolism (bone marrow, fat or thrombotic)
• Pneumonia
• CVA
• Sepsis

Differential Diagnosis

• Pneumonia
• Asthma
• Pulmonary hypertension

Sickle cell crisis

• Vaso-occlusive pain crisis
• Bony infarction
• Dactylitis
• Avascular necrosis of femoral head
• Acute chest syndrome
• Asthma
• Pulmonary hypertension
• Gallbladder disease
• Acute hepatic sequestration
• Infection
  • Meningitis
  • Pneumonia
  • Septic joint
  • Osteomyelitis
• Parvovirus B19
• Splenic sequestration
• CVA
• Cerebral aneurysm and ICH
• Priapism
• Papillary necrosis

Evaluation

Chest X-ray of TRALI (left) compared to the same subject after resolution of symptoms (right).

Work-Up

• CBC
• Retic count
• VBG / ABG
• Blood culture /sputum cultures
• CXR
• Type and screen/crossmatch

Imaging

• New infiltrate seen on chest x-ray
  • Chest x-ray findings may lag behind clinical features
• Lung ultrasound to CXR or CT finding correlations
  • Consolidation seen as hyperechoic punctiform air bronchograms
  • Ground-glass opacities seen as coalescent B lines
  • Pleural effusion, defined as large if interpleural distance > 25 mm
• Consider CTPE for persistent hypoxia with unclear cause

Management

• O2
  • Titrate to pulse oximetry >95%
  • NNoninvasive or invasive positive pressure ventilation may be required in severe cases
• Hydration
  • Oral hydration preferred
  • IV hydration with hypotonic fluid if patient unable to tolerate PO
    • Consider D5 + 1/2 Normal saline at 1-1.5x maintenance rate
  • While dehydration can predispose sickling, overhydration can cause pulmonary edema that exacerbates sickling
• Analgesia
  • Opioids often required for adults and sometimes needed for pediatrics
  • However, attempt to prevent oversedation and hypoventilation, atelectasis
• Incentive Spirometry
• Bronchodilators
• Antibiotics
  • 3rd generation cephalosporin + macrolide
• Simple Transfusion (leucocyte depleted)
  • Consider transfusion to goal of hemoglobin 11 / hematocrit 30 for:
    • O2 Sat <92% on room air
    • hematocrit/hemoglobin 10-20% below patient's usual values, or continuously dropping hematocrit/hemoglobin
• Exchange transfusion
  • Consider for:
    • Progression of acute chest syndrome despite simple transfusion
    • Severe hypoxemia
    • Multi-lobar disease
    • Previous history of severe acute chest syndrome or cardiopulmonary disease
  • Can prevent the need for intubation

Disposition

• Admission
• Consider consultation to hematologist

See Also

• Sickle Cell Crisis

External Links

• IBCC Chapter on Acute Chest Syndrome