Acute Chest Syndrome (Sickle Cell Disease)

• Pathophysiology essentially involves sickling within the pulmonary vasculature, leading to vasoocclusion, ischemia, and endothelial injury.  Recurrent episodes can lead to parenchymal fibrosis. 

• #1 cause of death in adults with sickle cell disease.

Etiologies of Acute Chest Syndrome:
Majority are idiopathic.  But, of those with identified cause:
1. Infection – both bacterial (including atypicals) and viral etiologies
2. Pulmonary Infarction
3. Fat embolism from infarcted bone

Note, sickle cell patients with asthma (as our patient) are at increased risk for Acute Chest Syndrome.
Interestingly, ½ of cases occur in patients hospitalized for other reasons (usually a vasoocclusive crisis), within 24-48 hours – therefore, repeat CXR’s are often in order for patients who present with chest pain!

Diagnosis of Acute Chest Syndrome:

• New pulmonary infiltrate on CXR (that is not atelectasis)

PLUS one of the following:
1. Chest Pain
2. Fever > 38.5
3. Tachypnea, wheezing, cough, or increased work of breathing
4. Hypoxemia

Management of Acute Chest Syndrome:
1. IVFs – similar to routine pain crises, goal is to achieve euvolemia first with isotonic fluids, then maintenance fluids.  Avoid overhydration which can lead to pulmonary edema.
2. Pain control – goal is to prevent hypoventilation due to splinting, leading to atelectasis and more hypoxemia.  Toradol is a good option, and patients often require a dilaudid PCA (But careful to avoid oversedation and hypoventilation).
3. Supplemental oxygen, incentive spirometry, bronchodilators
4. Empiric antibiotics – since infection is a common trigger for ACS, and it is basically impossible to distinguish PNA from ACS.  Usually, CAP coverage (Levofloxacin/Moxifloxacin or CTX/Azithromycin) is reasonable, but since these patients are often in and out of the hospital, they may require broader HCAP coverage.
5. ?Steroids? – may be beneficial in mild-moderate ACS, but conflicting data, including some data which show an increased rate of readmissions.  However, since asthma is a common comorbid condition, a short course of steroids may be beneficial for that reason.
6. Transfusions – Idea is to transfuse non-sickled blood and improve oxygenation. 

• Can be done both via simple transfusion or exchange transfusion.

• General indications for exchange transfusion: Acute chest syndrome with severe pain refractory to simple transfusion, severe hypoxemia, multi-lobar disease, previous history of severe acute chest syndrome, or severe cardiopulmonary disease.

• Exchange transfusion involves “bleeding” the patient and replacing with an equal volume of isotonic fluids and donor RBCs to decrease % of HgS (ideally <30%).  There is data to support the use of exchange transfusion to improve mortality in acute chest syndrome and sometimes perioperatively (esp cardiac surgery).

• Hydroxyurea - the only agent that has been shown to decrease mortality and frequency of pain crises in SC anemia (primarily by increasing production of Hg F,thereby decreasing viscosity and vaso-occlusive events; also increases NO, which can help mediate the relative decrease in NO as free hemoglobin binds to it in chronic hemolysis).

(Chanu Rhee MD, 11/18/10)