Therapeutic Plasma Exchange Using Membrane Plasma Separation

Abstract

Therapeutic plasma exchange is a blood purification technique designed for the removal of large molecular weight toxins such as pathogenic antibodies and lipoproteins. Plasma exchange can be performed either by membrane separation or centrifugation. Centrifugal plasma exchange is more common in the United States, while membrane separation is more popular in Germany and Japan. The membrane separation technique is similar to the ultrafiltration procedures performed with a standard dialysis machine but in which the membrane's pores are large enough to allow removal of all circulating molecules while retaining the cellular components. The current availability of plasma separation membranes compatible with CRRT systems has dramatically increased the potential for almost all nephrologists to perform these treatments. This review describes the membrane separation techniques available in the United States, the practical aspects of ordering and operating a membrane separation plasma exchange procedure, and its possible complications.

Keywords: Antibodies; Artificial; Centrifugation; Kidneys; Lipoproteins; Molecular Weight; Nephrologists; Plasma Exchange; Plasmapheresis; clinical nephrology; renal dialysis; ultrafiltration.

Figure 1.

Schematic section of a hollow fiber for plasma exchange. Whole blood flows lengthwise along the interior of the fiber, whereas its plasma components, such as Igs, clotting factors, fibrinogen, and albumin, pass through the pores in the fiber wall and collect outside the fiber. The wall of the hollow fiber functions as the separating membrane with a pore size that allows penetration by plasma but not by the blood’s cellular components (red blood cells [RBCs], white blood cells [WBCs], and platelets).

Figure 2.

Blood flowing through the plasma filter, plasma separation and infusion of replacement solution, and return to the patient.

Figure 3.

Comparison between efficacy of membrane separation therapeutic plasma exchange (mTPE) and centrifugation therapeutic plasma exchange (cTPE). IgG and IgM levels before and after showing similar removal with the two techniques. Reprinted from ref. , with permission.

Figure 4.

Progressive decline in IgG levels after three consecutive plasma exchanges (1 plasma volume each). IgG increased between treatments due to the combination of extravascular to intravascular re-equilibration and new IgG synthesis. Reprinted from ref. , with permission.

Figure 5.

Relationship of plasma volume exchanged (V_e), estimated plasma volume (EPV), and percentage reduction in initial concentration for pathogenic molecules removed during therapeutic plasma exchange. V_e/EPV=1 (i.e., 1 plasma volume will remove 63% of the pretreatment concentration of the molecule). V_e/EPV=1.4, or 1.4 plasma volume will remove 75% of the substance. Reprinted from ref. , with permission.