Protective Hemoglobin Types

Fetal hemoglobin binds oxygen more tightly than HbA, and it has a decreased propensity to sickling. HbA2 also possesses this characteristic but to a lesser extent. RBCs that contain HbF sickle less readily than cells without. ISCs are found to have low HbF concentrations. In some patients, higher HbF may ameliorate the disease.

FIGURE 68-3. Pathophysiology of SCD. (Arg, arginine; ET-1, endothelin-1; Hb, hemoglobin; NO, nitric oxide; NOS, nitrous oxide synthase; VCAM-1, vascular cell adhesion molecule 1; XO, xanthine oxidase.) (From Kato GJ, Gladwin MT. Sickle cell disease. In: Hall JB, Schmidt GA, Wood LDH, (eds.). Principles of Critical Care, 3rd ed. New York: McGraw-Hill, 2005:1658.)

FIGURE 68-3. Pathophysiology of SCD. (Arg, arginine; ET-1, endothelin-1; Hb, hemoglobin; NO, nitric oxide; NOS, nitrous oxide synthase; VCAM-1, vascular cell adhesion molecule 1; XO, xanthine oxidase.) (From Kato GJ, Gladwin MT. Sickle cell disease. In: Hall JB, Schmidt GA, Wood LDH, (eds.). Principles of Critical Care, 3rd ed. New York: McGraw-Hill, 2005:1658.)

Clinical Presentation and Diagnosis of SCT General

• Generally asymptomatic Symptoms

• Females may have frequent urinary tract infections Signs

• Microscopic hematuria occurs rarely

• Gross hematuria may occur spontaneously or with heavy intensity exercise Laboratory Tests

• Normal Hgb values

Other Pathophysiologic Effects

Other factors may be responsible for the pathogenesis of some of the clinical features of SCD. Sickle cells can obstruct blood flow to the spleen leading to functional as-

plenia. Impaired splenic function can increase the propensity to infection by encapsulated organisms, particularly Streptococcus pneumoniae. Additionally, coagulation abnormalities are not uncommon since almost every component of hemostasis is altered in SCD.

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