Читать книгу Transfusion Medicine - Jeffrey McCullough - Страница 163

Thomas Gniadek MD, PhD

Although collected whole blood can be separated into its component parts (e.g., plasma, platelets, and packed red blood cells [RBCs]), the amount of each component collected from a single donor is limited in this approach by the amount of whole blood that can be collected at one time. As the demand for blood components increased during the 1900s, especially in the field of oncology, much effort was devoted to developing methods to collect individual blood components from a donor, while minimizing their overall whole blood loss. These procedures were called apheresis, meaning “to take away.”

As early as 1914, Abel et al. [1] removed whole blood, retained the plasma, and returned the red cells to the donor, a procedure termed plasmapheresis. During the 1950s and 1960s, manual apheresis procedures were developed using combinations of the plastic bags and tubing sets developed for whole blood collection. A standard unit of blood was removed, the desired component (either plasma or platelets) separated, and the remainder of the blood returned to the donor; the process was repeated several times, producing a larger amount of the desired component than would have been obtained from one unit of whole blood [2]. The method was time consuming, cumbersome, and expensive; therefore, more automated methods were sought.

Semiautomated apheresis methods were developed generally by two separate research groups [3]. In Boston, the centrifuge apparatus developed for plasma fractionation by Edwin Cohn was modified to process whole blood from normal donors [4], and at the National Institutes of Health a blood cell separator was developed to aid in the treatment of leukemia [5]. Both of these approaches ultimately led to the sophisticated apheresis machines, sometimes called blood cell separators, in widespread use today.

During apheresis, a donor’s whole blood is anticoagulated as it is passes through the instrument where it is separated into components, typically red cells, plasma, and a leukocyte–platelet fraction. The desired fraction or component is removed, and the remainder of the blood is recombined and returned to the donor. Several liters of donor blood can be processed through the instrument, resulting in a larger amount of the desired component than could be collected from one unit (500 mL) of whole blood.

Several instruments are currently available for the collection of platelets, granulocytes,lymphocytes, red cells, peripheral blood stem cells (PBSCs), or plasma by apheresis (Table 6.1). Most of these instruments use centrifugation to separate blood components, some operate in a continuous flow and others with intermittent flow, some require two venipunctures (an outflow and return) and others only one venipuncture. The instruments are operated by microprocessors that control the various parameters, including blood flow rate, amount of the anticoagulant added to the whole blood entering the system, centrifuge conditions, among others. For many years, blood cell separators were designed to collect one component (usually platelets) at a time. Recently, the approach has changed so that instruments can collect several different components either one at a time or in various combinations (Table 6.1). This creates marvelous opportunities for more creative and efficient use of blood donations.