CP26 Sickle Cell Anemia

Definition

Sickle cell anemia is an alteration in the form and function of normal adult hemoglobin, which is replaced by Hbs.  In the normal adult, hemoglobin A is the predominant form of hemoglobin, comprising 96-97% of all hemoglobin.  Sickle cell hemoglobinopathy is a single gene-recessive abnormality that may be present in a heterozygous recessive form, which is sickle cell trait, or in a homozygous form, which is expressed as the sickle cell disease.  Patients with the homozygous form have a predominance of hemoglobin S, which may account for 80-98% of the hemoglobin.   In contrast, patients with the sickle cell trait have a lower percentage of hemoglobin S, accounting for 20-45% of their total hemoglobin.  Red blood cell sickling results from deoxyhemoglobin formation.  The tendency toward sickling increases hypoxemia, acidosis, increased concentrations of 2,3 DPG, infection, hypothermia, and capillary stagnation.  A hypertonic environment that may cause creation of normal blood cells will also lead to sickling in the abnormal cells.  The abnormal hemoglobin changes properties of the cell membrane, increasing osmotic and mechanical fragility.

Operative Management

               The operative strategy in sickle cell disease is to prevent sickling, and thereby prevent hemolysis or vasoocclusion phenomena.

Cardiopulmonary Bypass

1. Homozygous disease (exchange transfusion may be necessary).
2. Maintain adequate arterial oxygen tension/saturation.
3. Maintain adequate capillary perfusion, avoid low flow states.
4. Avoid low mixed venous saturations (maintain 80-85%).
5. Utilize moderate hemodilution to reduce blood viscosity.
6. Avoid acidosis shifts of the oxyhemoglobin dissociation curve.
7. Use moderate hypothermia (32*C) only.
8. Measure blood gases frequently, treat acidosis aggressively.
9. Use crystalloid cardioplegia (40mEq/L is a high dose).
10. Minimize the use of cardiotomy suction to decrease mechanical trauma.