Rheologic effects of plasma substitutes used for preoperative hemodilution

This study was designed to compare the influence of various plasma substitutes, administered for preoperative hemodilution, on blood rheology. We studied 40 patients, ASA grade I, who underwent elective facial reconstructive surgery and received 4% albumin (n = 10), 3.5% dextran 40 (n = 10), gelatin (n = 10), or hydroxyethyl starch (HES) (n = 10). Ten patients, undergoing the same surgical procedure without hemodilution, were chosen as controls. After hemodilution, hematocrit was decreased approximately 30%. Fibrinogen decreased in all tested groups except in the gelatin group. Plasma viscosity decreased with albumin (1.13 +/- 0.05 to 1.06 +/- 0.03 mPa.s; P < 0.01) and increased with HES (1.15 +/- 0.04 to 1.22 +/- 0.05 mPa.s; P < 0.01). At a high shear rate, the blood viscosity decreased in all groups. In contrast, at a low shear rate and at 40% corrected hematocrit, the blood viscosity decreased in the albumin (15.9 +/- 1.9 to 13.1 +/- 2.1 mPa.s; P < 0.01) and the dextran 40 (16.9 +/- 2.9 to 12.8 +/- 2.5 mPa.s; P < 0.01) groups and was unchanged in the gelatin and the HES groups. Erythrocyte aggregation (measured with primary aggregation time) was markedly decreased in the albumin (3.27 +/- 1.74 to 7.03 +/- 2.95 s; P < 0.01) and in the dextran 40 (2.72 +/- 0.58 to 6.24 +/- 2.55 s; P < 0.001) groups, unchanged with HES, and increased with gelatin (2.41 +/- 0.90 to 1.55 +/- 0.33 s). These findings suggest that albumin and dextran 40 may be the plasma substitutes of choice for preoperative hemodilution when this technique aims to improve rheologic conditions.