HEMATOLOGIC AND RHEOLOGIC ASPECTS OF ERYTHROPHERESIS(EP) FOR POLYCYTHEMIA (P)

Abstract

Fifteen EPs were performed on 11 pts (mean 8.6 yrs, range 2 mo-19 yr) with 5% albumin replacement. Hematocrit (HCT) was measured prior to, immediately after, and 6 hrs and 18-24 hrs after EP. Viscosity (V) of whole blood was measured at 37°C and at shear rates from 3 to 120 sec⁻¹ serially during EP in 4 pts, using a cone plate digital viscometer. The volume of EP was calculated from the equation: EP volume=TBV X[(HCT_I-HCT_D)÷HCT_I], where TBV=total blood volume, HCT_I=initial HCT, and HCT_D=desired HCT. All HCT values used were obtained from centrifuged central venous samples. The HCT achieved by EP correlated with the prospectively chosen HCT_D at an r value of 0.98. Mean exchange volume was 18.0±6.3%TBV. V was reduced by EP at all shear rates measured (p < 0.0005) and approached normal values at HCT < 55%. In pts with centrifuged central venous HCT>65%, HCT determined by Coulter method on central venous samples underestimated the HCT (68.3±4.6% vs 72.0±4.0%,p < 0.05); admission peripheral venipuncture Coulter HCT underestimated the HCT (66.5±4.8% vs 72.0±4.0%,p<0.01). The HCT remained unchanged 6 hrs after EP although a small but significant (p<0.05) increase occurred 18-24 hrs after EP. In pts with severe P (HCT>65%) it may be concluded that: 1) both central and peripheral venous Coulter determined HCT underestimate true central HCT; 2) using the centrifuged central venous HCT in the equation above, the EP volume to obtain the desired HCT can be determined accurately; 3) on completion of EP, HCT does not change 6 hrs after and increases only slightly after 18-24 hrs; and 4) adequate reduction in V is obtained by an EP volume sufficient to lower the HCT to 55%.

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