Therapeutic Plasmapheresis Calculator

Why Use

Can be useful to determine the number of plasma volumes to be exchanged to achieve a reduction in a targeted substance, particularly at the onset of a therapeutic plasma exchange procedure. Provides a sense of the futility of doing many plasma exchanges, as it shows the degree of diminishing returns once a plateau for efficient removal is reached.

When to Use

Patients who require therapeutic plasma exchange typically have a pathologic substance in circulation (e.g. an autoantibody) requiring removal. The amount of this substance remaining varies with the number of plasma volumes exchanged, with a plateau typically reached over time as the efficiencies of the procedure are reduced as higher amounts of replacement fluids are removed than the substance initially targeted.

Formula

Pearls / Pitfalls

This is a theoretical calculation applicable primarily to plasma exchange procedures; removal efficiencies will vary somewhat in practice based on what is being removed and its total body distribution. The equation assumes a strictly intravascular substance; this is not necessarily true in routine clinical practice and the less intravascular a substance, the poorer the efficiency of removal.

Advice

Discuss with apheresis nursing and technical staff the number of plasma volumes to be exchanged.