Membrane technology applied to donor plasmapheresis

Abstract

Membrane technology is being increasingly applied to the collection of plasma by plasmapheresis, a procedure in which plasma is separated from whole blood, and the cellular components reinfused to the donor. Although still somewhat controversial, there is a general understanding of the physics and fluid mechanics involved in the transport phenomena associated with the microporous filtration of whole blood. The filtration process is governed by concentration polarization, with the red blood cell being the polarizing species. Shear-enhanced cellular diffusion has been proposed to explain how such a large cell can depolarize to allow the observed separation rates. The filtration rate per unit area is proportional to the first power of the shear rate and therefore, can remain approximately constant if the shear rate is increased to accommodate a decrease in surface area. Three automated membrane-based plasmapheresis systems are currently in use, primarily at fixed-site locations. They all collect 500-600 cc of plasma within 30-50 min. Two use hollow fiber membrane filter modules, while the third uses a rotating cylinder which relies on Couette rather than Poiseuille flow to generate the required shear rates at the membrane surface. Two portable systems have been developed; one centrifuge-based system requires house current, the other membrane system uses gravity, augmented by a battery power source. Both of the latter systems, due to their size and low weight are well suited for use in an environment where the equipment is moved on a frequent basis.