Acute chest syndrome

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Acute Chest Syndrome is a vaso-occlusive crisis of the pulmonary vasculature commonly seen in patients with Sickle Cell Anemia. Acute Chest Syndrome is often initiated by a lung infection and the resulting inflammation and loss of oxygen tension leads to sickling of red cells and further vaso-occlusion. Acute Chest Syndrome is one of the most common causes of death for Sickle Cell patients.^[1]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

The term acute chest syndrome (ACS) was first proposed in 1979, by Charache et.al. ACS is the second most common cause of hospitalization in patients with sickle cell disease (SCD), and is responsible for up to 25% of deaths. Recurrent episodes have been associated with an increased risk of both chronic lung disease and early mortality. The Cooperative Study of Sickle Cell disease is a prospective study that followed 3,751 patients with SCD from 1979 through 1988. Vichinsky et.al., from that group, reviewed 1,722 cases of ACS in 939 patients. They defined ACS as a new pulmonary infiltrate on chest x-ray (CXR), or a defect on a perfusion scan, however, 99% of patients, were diagnosed with ACS on the basis of their CXRs.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

The SS genotype is associated with an increased incidence of ACS. See sickle cell anemia for more information regarding the genetics of the disease.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Genetics: The SS genotype is associated with an increased incidence of ACS.

See sickle cell anemia for more information regarding the genetics of the disease.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

• The primary acute pulmonary diseases which affect patients with SCD include pneumonia, infarction due to in-situ clot, fat / bone marrow emboli and ACS. Patients with SCD are predisposed to pneumonia due to loss of antibody protection (secondary to auto-splenectomy), and defective opsonization and phagocytosis resulting from a defect in the alternate pathway of complement activation. As blood and sputum cultures are often negative in any patient with pneumonia it is difficult to distinguish infection from ACS. However, unlike children, who have a higher incidence of infectious causes of ACS, adults are thought to have a higher incidence of vascular occlusion. One study that examined the causes of pulmonary infiltrates in patients with ACS with bronchoscopy, found a 21% incidence of bacterial infection. Interestingly, patients with SCD do not have a higher rate of large vessel fibrin thromboembolism compared with the general population. They do, however, have a higher rate of in-situ clot, and fat embolism. In-situ clot results from sickle cells being less deformable than normal cells, an increased adherence of sickle cells to the endothelial cells, and local vasoconstriction secondary to hypoxemia. Patients with SC disease have a higher rate of thrombosis as compared to those with SS disease, due to a higher blood viscosity and hematocrit. Fat embolism probably results from bone marrow infarction and is often associated with mental status changes, thrombocytopenia, a falling hematocrit (HCT), disseminated intravascular coagulation (DIC), hypocalcemia, hyperuricemia, and severe hypoxemia. Unfortunately, there is no test that will confirm the diagnosis of fat emboli. Lipemia retinalis and petechiae on the conjunctiva and upper thorax are suggestive of fat emboli syndrome. Bronchoalveolar lavage findings of greater than 5% lipid laden macrophages, and fat droplets obtained from a pulmonary capillary wedge aspirate are also highly suggestive, however their sensitivity and specificity remain to be define. Rib and sternal fractures or infarction can also precipitate ACS by causing splinting, atelectasis and hypoxemia. ^{[1] [2] [3] [4]}

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

• The incidence of ACS peaks in children 2-5 years old, and declines as patients age.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

• Factors associated with an increased incidence of ACS are:

  • The SS genotype
  • A higher steady-state white blood cell (WBC) count.
  • It seems that smoking status does not influence the incidence of ACS.
  • A higher level of Hb F may protect children younger than 2 years old.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

See sickle cell anemia

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

• Overall mortality in patients with ACS is 1.8%, however in adults the rate is 4.3%.
• There is no difference between patients with Hb SS and Hb SC.
• Unfortunately, there have been no presenting signs, symptoms or laboratory data that is predictive of who will die.
• A trend to increased mortality has been observed in patients with a lower presenting hemoglobin, multilobar involvement on CXR, and bacteremia.
• Patients who die, tend to do so very rapidly and unexpectedly.

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