Techniques

Cell separation by centrifugation

Blood is separated into components in a centrifuge. Plasma (or other specific blood components) are discarded and a plasma replacement fluid is infused in equal volume. Centrifugation may be continuous where blood is withdrawn and returned by separate needles, or intermittent where blood is withdrawn, separated and then returned via the same needle.

Membrane filtration

Plasma is continuously filtered through a large pore filter (molecular weight cut-off typically 1,000,000Da). The plasma is discarded and replaced by infusion of an equal volume of replacement fluid. The technique is similar to haemofiltration and uses the same equipment.

Replacement fluid

Most patients will tolerate replacement with a plasma substitute. Our preference is to replace plasma loss with equal volumes of 6% hydroxy-ethyl starch and 5% albumin. However, some use partial crystalloid replacement and others use all albumin replacement. Some fresh frozen plasma will be necessary after the exchange to replace coagulation factors. The only indication to replace plasma loss with all fresh frozen plasma is where plasma exchange is being performed to replace missing plasma factors.

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