928 cient disease management than that achieved with manual transfusion approaches Automated exchange transfusions also prevent dramatic increases in effective circulating volume and are associated wi[.]
C Taylan and S M Sutherland 928 a Fraction of plasma component (%) 100 90 80 70 60 50 40 30 20 10 0 Days b 100 Fraction of plasma component (%) Fig 48.2 Comparison of daily and alternate day plasma exchange regimens Figure 48.2a depicts daily, single- volume exchanges whereas Fig. 48.2b depicts alternate-day exchanges of 1.5x volume Similar effective clearances can be achieved over or 7 days, respectively While alternate day regimens allow greater inter-treatment rebound of pathologic blood components (i.e., autoantibodies), they also allow for synthesis and reaccumulation of physiologic compounds necessary for hematologic homeostasis (i.e., clotting factors) 90 80 70 60 50 40 30 20 10 0 cient disease management than that achieved with manual transfusion approaches Automated exchange transfusions also prevent dramatic increases in effective circulating volume and are associated with reduced risk for iron overload [18, 19] Leukapheresis Leukapheresis is the process by which leukocytes are removed from whole blood while the plasma, platelets, and red cells are returned to the patient Historically, the most common indication for leukapheresis has been malignancy-associ- Days 10 ated hyperleukocytosis Hyperleukocytosis in the setting of leukemia can cause severe pulmonary and neurologic complications; traditionally, rapid reduction of the leukocyte count by automated therapeutic leukapheresis was thought to reduce the risk of these complications through a reduction in circulating WBC mass and blood viscosity [20–22] Newer data, however, has suggested that leukapheresis may not significantly improve outcomes [23–25] Based upon the best currently available data, leukapheresis tends to be considered when the WBC count is >300–400×109/L [26–28]; if initiated, it is often performed until the WBC falls below 50–100×109/L [26, 28] Though its use in pediatric hematologic malig- 48 Therapeutic Apheresis in Children nancies can be debated, there is ample data to suggest that it can be performed safely even in very small children [26, 29] Additionally, variations of this leukapheresis technique can be used to harvest peripheral blood mononuclear cells from allogeneic or autologous donors for stem cell transplantation or cell-based therapies [30, 31] Leukapheresis allows harvest of peripheral blood progenitor cells which can then be used in stem cell transplantations Alternatively, leukapheresis can be used to harvest T-cell lymphocytes which are manipulated ex-vivo and used therapeutically in the setting of malignancy [32, 33] Plateletpheresis In plateletpheresis whole blood from healthy donors is separated into platelet-poor plasma (PPP), platelet-rich plasma (PRP), and red cells The PRP is retained as a single-donor platelet concentrate, while the PPP and red cells are returned to the donor This is the single most frequent application of apheresis technology and harvested platelets are used to treat thrombocytopenia of various causes and severities Plateletpheresis can also be used as a therapeutic procedure to remove excess platelets from the circulation in patients with symptomatic thrombocytosis [34, 35] Photopheresis Photopheresis is a specialized variation of the leukapheresis procedure In photopheresis, leukocytes are collected and then exposed to a photosensitizing agent and ultraviolet A light; the photo-activated leukocytes are then returned to the patient [36] When it was first introduced, the photosensitizing agent was administered systemically (orally); however, the currently employed procedure utilizes an agent which can be administered to the leukocytes ex vivo during the procedure [37] This has increased effectiveness and tolerability, the latter of which is especially significant in pediatric patients [10, 37] This therapy was first employed in the setting of cuta- 929 neous T-cell lymphoma [38–41] and has since been used to treat graft-versus-host disease, solid organ allograft rejection, and some autoimmune diseases [36, 38, 42–48]; in children, the most common indications are graft versus host disease and acute rejection of solid organ transplants [10] Although it has been utilized since the 1980s, the mechanism of action remains poorly understood [10, 37–39, 49, 50] The prevailing data suggests that the procedure mediates immunomodulation via induction of lymphocyte apoptosis [36, 37] At our institution (SMS), a closed photopheresis system is utilized (CELLEX®, Therakos, Mallinckrodt Pharmaceuticals, Bedminster NJ, USA) This device has a priming volume of ~ 250 mL and a blood prime is recommended for patients