1. ACUTE CHEST SYNDROME Dr.Padma Gadde Dr. Dora Alvarez

2. ACUTE CHEST SYNDROME  “ Acute chest syndrome" (ACS) broadly describes a disease  leading cause of death  second most common cause of hospitalization in patients with sickle cell disease

3. ACUTE CHEST SYNDROME  Its rapid clinical course, with or without fever, is characterized by chest pain, cough, progressive anemia, hypoxemia, and the presence of new pulmonary infiltrates on chest radiographs

4. Learning Objectives  To identify the causes of acute chest syndrome (ACS) in patients with sickle cell disease  To understand the pathophysiology of ACS  To recognize elements that are important in appropriate management of ACS

5. ACUTE CHEST SYNDROME  The approach to diagnosis, monitoring, and treatment requires (1) recognition of the complication, (2) correction, if possible, of inciting factors, (3) maintenance of euvolemia, (4) pain control, and (5) use of transfusions and (6) administration of oxygen, if needed.

6. ACUTE CHEST SYNDROME Risk factors  Younger age  Homozygous sickle cell or sickle cell-beta° thalassemia genotype  Winter months  Fever

7. ACUTE CHEST SYNDROME Risk factors  Surgery  Avascular necrosis of bone  Previous pulmonary events  High hemoglobin levels  High steady-state leukocyte counts  Low fetal hemoglobin concentration

8. Pathophysiology  The pathogenesis of parenchymal lung infiltrates in ACS is incompletely understood.  Pulmonary infiltrates may result from either one process or a combination of several interacting processes, which may include atelectasis, infection, fat embolism, thromboembolism and, most commonly, in situ microvascular occlusion within the pulmonary vasculature by sickled erythrocytes

9. Pathophysiology  The importance of nonembolic microvascular occlusion in causing ACS is demonstrated by findings on thin-cut computed tomographic scans: Arterioles and venules are either absent or diminished in number, and ground- glass opacities appear in a mosaic, patchy, or multifocal distribution

10. pathophysiology  Fat embolism from bone marrow necrosis seems to be an important and often unrecognized cause of ACS

11. pathophysiology  Patients with pulmonary fat embolism are more likely than others to have severe bone and chest pain, changes in mental status, and a prolonged hospital course.  A complete blood cell count in these patients shows more severe anemia and thrombocytopenia than in patients without pulmonary fat embolism, and chest radiographs reveal more multilobar infiltrates

12. pathophysiology  sPLA 2 liberates free fatty acids from phospholipids.  Measurement of secretory phospholipase A 2 (sPLA 2 ) levels may be helpful, because they have recently been found to be elevated in patients with sickle cell disease and ACS from pulmonary fat embolism

13. pathophysiology  An early rise in these levels precedes the development of ACS and thus may be a useful marker in predicting its occurrence.  Furthermore, sPLA 2 levels correlate with disease severity.

14. Mechanisms of hypoxemia  Hypoventilation due to  Direct chest-wall splinting from either rib and sternal infarctions or abdominal crisis  Excessive sedation from narcotic analgesics, leading to decreased oxygen exchange

15. Mechanisms of hypoxemia  Ventilation-perfusion mismatch possibly caused by diseases that underlie or result from acute chest syndrome  Pneumonia  Mucous plugging  Aspiration  Bronchospasm  Pulmonary hypertension  Cor pulmonale

16. Mechanisms of hypoxemia  Impaired oxygen diffusion from repetitive episodes of acute chest syndrome that ultimately result in restrictive lung disease (2,3)

17. Evaluation  ACS is more severe in adolescents and adults than in children.  Patients most commonly present with shortness of breath, chills, and pleuritic chest pain, but no fever

18. Evaluation  In some cases, physical signs of disease are delayed and are first noted during hospitalization.

19. Evaluation These include  chest-wall tenderness secondary to rib infarction.  dullness to percussion caused by pleural effusion.  and auscultatory rales from pulmonary consolidation.

20. Evaluation Results of laboratory studies may show  anemia with thrombocytopenia  or thrombocytosis,  leukocytosis,  and evidence of hemolysis, including elevated LDH bilirubin levels

21. Evaluation  Findings on chest radiographs, although not pathognomonic, include patchy lower-lobe involvement in a segmental, lobar, or multilobar distribution, with or without pleural effusion.  Correlation between the extent of consolidation found on chest radiographs and the severity of hypoxemia is poor

22. Evaluation  The presence of bilateral pulmonary infiltrates, however, identifies a subset of patients who are more likely to have serious illness.  Their clinical course is characterized by tachycardia, protracted hypoxemia, longer duration of fever, and a greater fall in hemoglobin levels

23. Diagnostic tests for acute chest syndrome  Sputum analysis for Gram's stain  Blood cultures  Chest radiographs  Thin-cut computed tomographic scan of chest  Serial measurement of arterial blood gases  Ultrasound or impedance plethysmography  Bone scan  Flexible bronchoscopy with bronchoalveolar lavage

24. Management of acute chest syndrome in patients with sickle cell disease  Identify and treat all underlying precipitating factors  Maintain adequate oxygenation, improve oxygen-carrying capacity, and improve tissue oxygen delivery Administer supplemental oxygen to maintain PaO 2 in 70-100 mm Hg range

25. Management of acute chest syndrome in patients with sickle cell disease  Give simple or exchange transfusion to enhance oxygen capacity or reduce hemoglobin S concentration to reverse episodes  For severe respiratory failure, use mechanical ventilation with positive end-expiratory pressure (PEEP) or continuous positive airway pressure (CPAP

26. Management of acute chest syndrome in patients with SSD  Prevent further alveolar collapse by using incentive spirometry, CPAP, and PEEP  Maintain adequate fluid volume Give hypotonic saline (D 5 W or 5% dextrose in 0.25% normal saline) to maintain normovolemic state

27. Management of acute chest syndrome in patients with SSD  Control pain Give adequate amounts of narcotic analgesics to alleviate pain, avoiding hypoventilation from excessive sedation  Nonsteroidal anti-inflammatory medications (if not contraindicated by underlying peptic ulcer or renal disease)  Morphine sulfate, 0.1-0.15 mg/kg every 3-4 hours intravenously, through fixed scheduling or patient-controlled analgesia

28. Management of acute chest syndrome in patients with SSD  Treat underlying infection Provide empirical coverage for community- acquired pneumonia, pending results from other studies; use second- or third-generation cephalosporin or selected beta-lactam/beta- lactamase inhibitor in combination with macrolide  Prescribe bronchodilator Use albuterol (Airet, Proventil, Ventolin) through metered-dose inhaler or nebulizer

29. Management of acute chest syndrome in patients with SSD  Fluid administration If the patient is unable to consume fluids orally, 5% dextrose in water or 5% dextrose in 0.25% normal saline solution should be administered intravenously to maintain euvolemia once any existing volume deficits have been corrected.

30. Management of acute chest syndrome in patients with SSD  Dehydration must be remedied, because it can result in increased plasma osmolarity and intracellular dehydration of red blood cells.  Under those conditions, erythrocytes are more likely to sickle. Hypotonic saline solutions are used because free water enters the relatively hypertonic red blood cells.  This process causes osmotic swelling, decreased mean corpuscular hemoglobin concentration and, consequently, a reduced tendency for sickling.

31. Management of acute chest syndrome in patients with SSD  Decisions regarding transfusion are best guided by the patient's clinical condition.  Simple transfusion is indicated for patients with mild to moderate ACS; the goal is a hemoglobin value of 10 g/dL  Exchange transfusions should be reserved for severe crises, when it is important to decrease the hemoglobin S concentration rapidly.  Unlike simple transfusions, exchange transfusions avoid the problems related to increased blood volume and viscosity. It is suggested that a PaO 2 of less than 60 mm Hg, clinical deterioration, or a worsening condition seen on chest radiographs should prompt exchange transfusion.

32. Management of acute chest syndrome in patients with SSD  The goal is to reduce the hemoglobin S concentration to 20% to 30% and the hematocrit to 30% (5). Patients with recurrent episodes of ACS may also benefit from regular exchange transfusions to maintain the hemoglobin S concentration below 30%.