Apheresis Machine

Overview

An apheresis machine separates blood into its components and keeps only the one that is wanted, returning everything else to the person. The word comes from the Greek for "to take away". In a platelet donation, for example, the machine draws whole blood, spins out the platelets, and gives the donor back their red cells and plasma; in therapeutic plasma exchange it removes a patient's plasma, carrying a disease-causing antibody, and replaces it with donor plasma or albumin. Because only the targeted fraction is taken, donors recover faster and larger yields of a single component are possible than from a whole-blood donation.

The machine combines a Centrifuge Channel System for separation, a Pump Set and Valve Block to move and route fluids, a Sensor Suite to control quality and safety, and a Disposable Kit Interface that holds the sterile single-use blood path.

Separation by centrifugation

Blood components differ in density: red cells are heaviest, plasma lightest, and the platelet- and white-cell-rich buffy coat lies between. The Centrifuge Channel System exploits this. Blood enters the spinning Rotor Bowl, where forces of several thousand g stratify it into layers within seconds. A key design feature is the Sealless Rotating Coupling: rather than a sliding seal, which would shed particles and risk contamination, the fluid lines loop into the rotor so the tubing twists but never breaks its sterile boundary. The Centrifuge Motor holds a precise speed under closed-loop control, and an Imbalance Sensor stops the rotor immediately if the load goes off-balance.

Most modern devices run continuous-flow: blood is drawn, separated, and returned simultaneously, so the extracorporeal volume stays small, around 200 mL. The Interface Detector optically watches the boundary between layers inside the channel and steers the Collect Pump to skim exactly the target layer, keeping the product pure and free of contaminating cells.

Fluid handling

The Pump Set is a bank of peristaltic pumps, each squeezing a length of disposable tubing so nothing mechanical touches the blood. The Draw/Return Pump moves whole blood in and components back out, the Plasma Pump and Collect Pump handle the separated fractions, and the Anticoagulant Pump meters citrate anticoagulant into the draw line. Anticoagulation is essential because blood clots on contact with foreign surfaces; citrate works by binding calcium, which the clotting cascade needs, and it is added at a fixed ratio to blood flow, typically one part anticoagulant to eight or more parts blood. The Valve Block of pinch valves opens and closes tubing paths to switch the machine between drawing, separating, collecting, and returning, again without ever contacting the fluid.

Safety monitoring

Returning blood and fluids to a living person makes safety sensing central. The Air Detector on the return line stops the pump if it senses air, preventing embolism. The Plasma Leak Detector watches for red cells escaping into a line where only plasma should be, which flags a separation fault. Three Pressure Sensor channels monitor access, return, and channel pressures so a kinked line or a failing vein is caught early, and the Hematocrit Sensor reads the inlet red-cell fraction to optimise separation. A common physiological effect is citrate toxicity: because citrate binds calcium, donors can feel tingling, and the machine paces the return and prompts calcium replacement accordingly.

Disposable kit and operation

Everything that touches blood is part of the single-use Disposable Tubing Kit, loaded onto the Disposable Kit Interface. Its Cassette Mount seats the fluid cassette against the pumps and valves, the Bag Hangers hold anticoagulant, saline, and collection bags on Weigh Scales, and a Kit ID Reader confirms the right kit for the chosen procedure. The operator runs the whole sequence from the Console touchscreen, which displays flows, collected volume, and citrate dose. The Fluid System tracks every fluid by weight and, in plasma exchange, warms the replacement fluid through the Fluid Warmer. If mains power is lost, the Power System battery carries the machine through a safe return cycle so the patient's blood is given back rather than stranded in the circuit.