Just like most instruments and devices, medical technology continually changes to accommodate a safer, more efficient, and cost-effective method of procedure. Much is the same with the development of the leukapheresis machine. Overall, these machines, complex in their making, aim to efficiently collect targeted blood components with the purest of volume and shortest donation time.
Due to relevance, closed-loop, continuous and intermittent flow collection systems will be discussed in this section. However, it is important to note a brief history in the development of these machines. Starting with the American Instrument Company, early versions of the leukapheresis machine began with the Aminco Celltrifuge: a simpler system without a reservoir component that had donors bleeding continuously. The NCI-IBM Blood Cell Separator fixed this issue by providing a reservoir system that had donors bleeding intermittently with blood flow into a centrifuge system cycling continuously. The Model 2997 by IBM went on to tackle the obstacle of durable, removable parts in constant need of sterile cleaning by replacing them with disposable, hollow plastic blood separation channels to form the first official closed loop system.
Companies like Haemonetics and COBE then began developing their own versions of this accessible closed loop system with disposable compartments. Microprocessors were added to the mix to help control the operation of popular models like the COBE Spectra MNC, COBE Spectra Optia MNC, Spectra Optia IDL, Fenwal Amicus, Fenwal Alyx, Caridian Trima Accel, and the Haemonetics systems that are being used today for apheresis procedures.
Leukapheresis machines are now automated to begin and end collection times based on product volume. Product volume can either be a fixed volume per collection time (according to the machine’s setting) or based on function of the number of target cells (as studied between two popular COBE leukapheresis machines: Spectra MNC and Spectra Optia MNC). So collection times for donors will differ depending on the machine, although all machines will stop automatically when the desired yield has been reached.
Each leukapheresis machine has similar, basic components that help separate the inflow whole blood, collect targeted blood components, and return outflow vital material back to the donor. Although each machine will differ in the specifics, including but not limited to the type of microprocessor and centrifuge See LEUKAPHERESIS HISTORY for more information. LEUKAPHERESIS GUIDE 14 speed and size, the basic components are noteworthy for understanding how leukapheresis works.
Blood Separation Chamber: Blood first exits the vein, through either peripheral access from a sterilized needle and cannula or central access from a stabilized catheter. It then enters the leukapheresis machine where blood is first segregated in a blood separation channel or chamber. Leukodepletion, the reduction of leukocytes or the desired target cell, occurs here by centrifugation where gravity and a high-speed, rotating bowl help to pack the desired target cells and separate them from the unwanted material. Some machines, like the Cardian Trima Accel, contain leukoreduction filters that platelets can pass through to a storage bag.
Flow Pump: Pneumatic flow pump systems help to control blood flow into the blood separation chamber and subsequent centrifuge system. These pumps adjust to balance between inflow and outflow volumes. Some models, like the Fenwal Alyx, use internal sensors that monitor the weight of blood, fluids, and collection components. The pumps and subsequent sensory systems help maintain a steady inflow and outflow of extracorporeal blood so the machine will not experience overflow and the donor will not experience hypovolemia.
Centrifuge Bowl: Centrifugation is a collection bowl that spins at incredibly high speeds to help separate materials of variable weights by gravity. Materials will either “pull up” or “pull down” on the sides of the bowl depending on their specific gravities. This portion of the machine, pivotal to the separation process and made with disposable materials in the Haemonetics Instruments, is where the bulk of the leukapheresis work is done. The Haemonetics Instruments will spin inflow blood at a higher than average rate of 4800 rpm (rotations per minute) to continuously separate blood as it enters the bowl. Once the separated blood reaches a certain volume in the bowl, accumulated platelets, plasma, and RBCs move toward the exit port where they are diverted to a separate collection bag. Once this collection bag reaches a specific volume, blood flow is stopped and the sensory pumps reverse to return the recombined platelet and blood mixture back to the donor. In the Haemonetics Instruments, this centrifugation process is repeated several times to obtain desired yield.
Elutriation Chamber: Part of centrifugation, the elutriation chamber uses gas or liquid to help with the separation process based on cellular size. Uniquely placed in the center of the centrifugation bowl, the gas or liquid usually flows in the opposite direction of the desired target cell. Anticoagulants like ACD (anticoagulant-citrate-dextrose) are pumped here to intensify the separation process and keep the RBC, plasma, and platelet components from coagulating outside the body to be readily available for return.
Collection Bags: Storage of the desired yield and returnable materials are integral to the leukapheresis process. These materials are collected in disposable collection chambers where the desired yield of leukocytes that remain extracorporeal will be ready for storage while the remaining materials will be return back to the donor.
Certain terms frequent resources prevalent to the mechanics of these systems that require further dissection and understanding.
Collection Efficiency, or CE, refers to the total number of target cells collected post-apheresis. This number, presented as a percentage, can be found mathematically using product volume (PV), total processed blood volume (TPV), MNC pre-apheresis, and MNC post-apheresis.
CE (%) = (MNC/μL product x PV) / (((MNCpre + MNCpost)/2)xTPV)
Platelet Attrition, or PLT attrition, refers to the weakening of the accounted platelets (PLT). This number, presented as a percentage, can be found mathematically with the following equation.
PLT attrition (%) = ((PLTs/μL pre – PLTs/μL post) / (PLTs/μL pre)) x 100
Product Purity refers to the frequency of target cells per total white blood cells that can be represented as a percentage. The higher the percentage, the higher targeted cells per volume.
It is important to fully read and understand the manufacturer settings and guides to run any type of leukapheresis machine. Each machine has factory-set variables for collection and manufacturerrecommended collection preferences that will optimally run the system. Studies have shown that manipulation with these settings and off-label usage of the machine does not produce better results in quality or quantity of product and most collections proceed with minimal operational dysfunctions.
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