Page 2012 - Hematology_ Basic Principles and Practice ( PDFDrive )

Chapter 118 Hemapheresis 1783

substitution of a single amino acid. Although the defect appears
simple, the pathophysiology of the vasoocclusive crises is complex,
involving Hb polymerization, change in cell shape, adhesion to
endothelial cells, dysregulated nitric oxide homeostasis, and release
3
of free Hb and inflammatory cytokines. Clinical manifestations vary
from patient to patient. The rationale behind exchange transfusion
involves improving tissue oxygenation, reducing hemolysis, and
preventing microvascular sickling by diluting the patient’s abnormal
RBCs, simultaneously correcting anemia and favorably altering
whole blood viscosity and rheology. No clinical data support a single
optimal level of HbA; however, as few as 30% of transfused cells
markedly decrease blood viscosity. At mixtures of 50% or greater,
resistance to membrane filterability approaches normal. In nonemer-
gency situations, such levels can often be achieved with a simple
transfusion regimen. For simple and exchange transfusions, raising
the level of HbA to between 60% and 70% while lowering the level
of HbS to 30% is generally efficacious, although even higher levels
of HbA are often used to treat an ongoing crisis. Clinical indica-
tions for exchange transfusion in patients with sickle cell anemia
remain controversial, with limited controlled study data available.
Simple transfusion has been shown to improve renal concentrating
ability and splenic function in young sickle cell patients; exchange
transfusion improves exercise tolerance and reverses the periodic
oscillations in cutaneous blood flow associated with this disease.
Such observations have encouraged the use of exchange transfusion
for acute complications of sickle cell disease such as acute chest
syndrome, priapism, cerebrovascular accident, and hepatic and retinal
infarction. Exchange transfusion for sickle cell patients has also been
Fig. 118.4 TWO-STAGE THERAPEUTIC PLASMAPHERESIS. Plasma used for prophylaxis during pregnancy and before surgery, although
is separated from cells by filtration and then passed through parallel adsorp- prophylactic transfusion in these settings remains controversial. The
tion columns to remove low-density lipoproteins from a patient with only randomized trial of transfusion during pregnancy has shown that
homozygous familial hypercholesterolemia. prophylactic transfusion sufficient to reduce the incidence of painful
crises did not reduce other maternal morbidity or perinatal mortality.
The risk of intrauterine growth restriction may be reduced by pro-
TABLE Common Indications for Therapeutic Cytapheresis phylactic exchange transfusion; however, the study is limited by the
118.1 retrospective observational nature of the data. In a randomized study
of patients with sickle cell disease undergoing surgery, a conservative
Erythrocytapheresis simple transfusion regimen (to increase the Hb level to 10 g/dL) was
Acute complications of sickle cell disease as effective as an aggressive regimen (to lower the HbS level to <30%)
Prophylaxis for recurrent stroke with respect to perioperative complications not related to transfusion.
Frequent severe pain crises The patients in the aggressive regimen group received twice as many
Hyperparasitemia (malaria, babesiosis) units of blood, had a proportionally increased RBC alloimmunization
Hemochromatosis rate, and had more hemolytic transfusion reactions. A subsequent
Leukapheresis trial has confirmed that preoperative transfusion is associated with
Leukemia with hyperleukocytosis syndrome decreased perioperative complications in patients with sickle cell
Cutaneous T-cell lymphoma (photopheresis) disease who are scheduled to undergo low-risk and medium-risk
Peripheral blood stem cell collection surgeries. 4
Plateletpheresis Transfusion prophylaxis is now clearly indicated for children at
Symptomatic thrombocytosis high risk for stroke. A randomized controlled study demonstrated a
risk reduction of 90% in the patients who were maintained at levels
of 30% or less HbS by simple or exchange transfusion. This result
confirms earlier experience and indicates that in this group of children
apheresis immunoabsorption columns, which selectively remove with sickle cell anemia, transfusion therapy should begin before the
immunoglobulins in the plasma by binding to a solid matrix. first event and continue indefinitely. A second trial addressed whether
transfusion could be safely discontinued to avoid the cumulative
long-term risks of iron overload and RBC alloimmunization. After
Erythrocytapheresis 10 months of randomization, half of the patients who discontinued
transfusion had developed central nervous system abnormalities,
RBC exchange (erythrocytapheresis) is used most often to manage or including reversion to abnormal transcranial Doppler findings and a
prevent the acute vasoocclusive complications of sickle cell disease. small number of strokes, necessitating early termination of the trial.
Compared with manual exchange transfusion, mechanical cell separa- For chronic management, repeated erythrocytapheresis may be
tors offer the advantages of speed and ease and reduce the risks of preferable to simple transfusion for patients at high risk for stroke
rapid blood volume alteration and increased blood viscosity that may who have developed iron overload to levels associated with organ
occur with simple transfusion. Automated procedures can be per- damage. Exchange transfusion, although relatively safe and conve-
formed with all centrifugal instruments, and programmed procedures nient, carries all the complications of RBC transfusion. Patients are
allow accurate prediction of target hemoglobin (Hb) concentration exposed to a large number of donors and are at a small but significant
and percent HbA at the conclusion of the procedure. A single volume risk of contracting hepatitis and other blood-borne infections. As
exchange will remove about two-thirds of the circulating cells. many as 33% of all patients develop alloantibodies, and life-
Sickle cell anemia occurs in individuals who are homozygous threatening delayed hemolytic transfusion reactions have been
for a single mutation in codon 6 of the β-globin gene, resulting in reported. In addition, an immunohematologic study of multiply