Plasma exchange in acute and chronic hyperviscosity syndrome: a rheological approach and guidelines study

Therapeutic plasma exchange is an extra-corporeal technique able to remove from blood macromolecules and/or replace deficient plasma factors. It is the treatment of choice in hyperviscosity syndrome, due to the presence of quantitatively or qualitatively abnormal plasma proteins such as paraproteins. In spite of a general consensus on the indications to therapeutic plasma exchange in hyperviscosity syndrome, data or guide lines about the criteria to plan the treatment are still lacking. We studied the rheological effect of plasma exchange in 20 patients with plasma hyperviscosity aiming to give data useful for a rational planning of the treatment. Moreover, we verified the clinical applicability of the estimation of plasma viscosity by means of Kawai's equation. Plasma exchange decreases plasma viscosity about 20-30% for session. Only one session is required to normalize plasma viscosity when it is < 2.2 mPas, whereas a maximum of 3 session are required when it is > 2.2 till to 6 mPas. A fourth session is useless, especially if the inter-session interval is < 15 days. By means of a polynomial equation, knowing basal-plasma viscosity and the disease of a patient, we can calculate the decrease of viscosity obtainable by each session of plasma exchange then the number of session required to normalize the viscosity. Kawai's equation is able to evaluate plasma viscosity in healthy volunteers, but it is not clinically reliable in paraproteinemias.