Acute Chest Syndrome: Respiratory syndrome characterized by the appearance of a new pulmonary infiltrate on chest x-ray, accompanied by symptoms of fever, cough, chest pain, tachypnea, or DYSPNEA, often seen in patients with SICKLE CELL ANEMIA. Multiple factors (e.g., infection, and pulmonary FAT EMBOLISM) may contribute to the development of the syndrome.Anemia, Sickle Cell: A disease characterized by chronic hemolytic anemia, episodic painful crises, and pathologic involvement of many organs. It is the clinical expression of homozygosity for hemoglobin S.Chest Pain: Pressure, burning, or numbness in the chest.Embolism, Fat: Blocking of a blood vessel by fat deposits in the circulation. It is often seen after fractures of large bones or after administration of CORTICOSTEROIDS.Hemoglobin SC Disease: One of the sickle cell disorders characterized by the presence of both hemoglobin S and hemoglobin C. It is similar to, but less severe than sickle cell anemia.Antisickling Agents: Agents used to prevent or reverse the pathological events leading to sickling of erythrocytes in sickle cell conditions.Syndrome: A characteristic symptom complex.Lung Diseases: Pathological processes involving any part of the LUNG.Sickle Cell Trait: The condition of being heterozygous for hemoglobin S.Acute Disease: Disease having a short and relatively severe course.Hydroxyurea: An antineoplastic agent that inhibits DNA synthesis through the inhibition of ribonucleoside diphosphate reductase.Hemoglobin, Sickle: An abnormal hemoglobin resulting from the substitution of valine for glutamic acid at position 6 of the beta chain of the globin moiety. The heterozygous state results in sickle cell trait, the homozygous in sickle cell anemia.Pain: An unpleasant sensation induced by noxious stimuli which are detected by NERVE ENDINGS of NOCICEPTIVE NEURONS.Blood Transfusion: The introduction of whole blood or blood component directly into the blood stream. (Dorland, 27th ed)Fetal Hemoglobin: The major component of hemoglobin in the fetus. This HEMOGLOBIN has two alpha and two gamma polypeptide subunits in comparison to normal adult hemoglobin, which has two alpha and two beta polypeptide subunits. Fetal hemoglobin concentrations can be elevated (usually above 0.5%) in children and adults affected by LEUKEMIA and several types of ANEMIA.Respiratory Insufficiency: Failure to adequately provide oxygen to cells of the body and to remove excess carbon dioxide from them. (Stedman, 25th ed)Pulmonary Embolism: Blocking of the PULMONARY ARTERY or one of its branches by an EMBOLUS.Hemolysis: The destruction of ERYTHROCYTES by many different causal agents such as antibodies, bacteria, chemicals, temperature, and changes in tonicity.Fever: An abnormal elevation of body temperature, usually as a result of a pathologic process.Leukocytosis: A transient increase in the number of leukocytes in a body fluid.Retrospective Studies: Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons.Triage: The sorting out and classification of patients or casualties to determine priority of need and proper place of treatment.Cohort Studies: Studies in which subsets of a defined population are identified. These groups may or may not be exposed to factors hypothesized to influence the probability of the occurrence of a particular disease or other outcome. Cohorts are defined populations which, as a whole, are followed in an attempt to determine distinguishing subgroup characteristics.Acute Coronary Syndrome: An episode of MYOCARDIAL ISCHEMIA that generally lasts longer than a transient anginal episode that ultimately may lead to MYOCARDIAL INFARCTION.Emergency Service, Hospital: Hospital department responsible for the administration and provision of immediate medical or surgical care to the emergency patient.Tomography, X-Ray Computed: Tomography using x-ray transmission and a computer algorithm to reconstruct the image.