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Therapeutic Erythrocytapheresis and Red Cell Exchange
Therapeutic erythrocytapheresis (ET) is a procedure in which patients’ RBCs are selectively removed to reduce excessive RBC mass. It has been used for treatment of polycythemia vera, reactive erythrocytosis, and hereditary hemochromocytosis.
RBC exchange (RBCx) is a procedure in which the patient’s RBCs are replaced with allogeneic RBCs. RBCx is mostly used to treat patients with sickle cell disease (SCD). RBCx is safe; however, use of allogenic RBCs as replacement fluid places patient at risk for transfusion-associated adverse events. Recently, a modified RBCx procedure, termed isovolemic hemodilution (IHD) or depletion RBCx, has been introduced for patients with SCD to reduce number of RBC units used during procedure and/or lengthen time between procedures.
ET and RBCx may be performed manually or with automated system (this chapter addresses automated procedures).
Exchange Volume and Replacement Fluids
Fluid exchange volume is automatically calculated by the device as function of clinical parameters (e.g., patient’s gender, height, weight, and Hct), type of replacement fluid used (including replacement fluid Hct), desired postprocedure Hct, and desired fraction of cells remaining (FCR, which is defined as ratio of target patient’s RBCs remaining over initial RBCs). Typically, the goal in patients with SCD is final hemoglobin S (HbS) ≤30%; therefore, if the patient’s initial HbS is 100%, FCR would be set at 30%. FCR is dictated by preexchange HbS, and desired final HbS percentage; for example, if preexchange HbS is 60% with HbS goal of 30%, then FCR would be 50%. Most apheresis devices additionally require entry of goal end Hct. For patients with SCD, this value should be ≤30% to prevent hyperviscosity.
Because IHD involves RBC depletion followed by exchange, IHD RBCx should only be performed in stable patients because hypotension may occur during the depletion phase. During depletion phase, the patient’s Hct is lowered to safe target Hct (typically the higher of 8% less than initial Hct or 22%) using either 5% albumin or 0.9% normal saline to maintain blood pressure. Once target Hct is reached, device begins exchange procedure using RBC units as replacement fluid.
For all RBCx procedures, leukoreduced RBC products are recommended as replacement fluid, to mitigate potential alloimmunization and febrile reactions. RBC unit Hct varies with anticoagulant-preservative solution. In children, Hct of each unit is typically determined, and subsequently averaged to obtain replacement fluid Hct, enabling accurate prediction of postprocedure Hct.
In clinically unstable patients, priming exchange the set with 5% albumin before starting the procedure is advisable. Using 5% albumin conserves RBCs, simplifies procedure, and returns the patient’s blood mixed with albumin as opposed to saline. However, in severely anemic patients, priming with RBCs is recommended. For ET, 5% albumin and/or 0.9% saline may be used to maintain intravascular volume and hemodynamic parameters.
Indications
ABO Incompatible (Minor Incompatibility)
HPC ABO minor incompatibility occurs when the donor’s plasma contains antibodies against the recipient’s RBCs. To prevent or treat passenger lymphocyte syndrome, where donor lymphocytes secrete antibodies resulting in hemolysis, RBCx can be performed replacing recipient RBCs with group O RBCs. Goal is recipient RBCs <35%, 1 RBC volume exchange.
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