Does Hemodilution Enhance or Compromise Blood Coagulation?

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Abstract
The reduction in oxygen-carrying capacity during hemodilution is well tolerated by most patients. However, hemodilution not only decreases O2 transport capacity, but also may influence blood coagulation. Advanced hemodilution with crystalloids does not compromise blood coagulation and, with moderate hemodilution, even augmented blood coagulation may develop. In contrast, blood coagulation is compromised during hemodilution with colloids. The effect of human serum albumin and gelatin is relatively modest, but significantly more than during equivalent hemodilution with crystalloids. Dextran and hydroxyethyl starch compromise blood coagulation more. This results from reduction of factor VIII, a decrease in plasmatic coagulation, and an impairment of platelet function. For hydroxyethyl starch, molecular size and degree of substitution are crucial for the effect on blood coagulation, with hydroxyethyl starch (200,000/0.5) having the least effect. Furthermore, accelerated fibrin formation is observed during hemodilution with Dextran, hydroxyethyl starch, and gelatin with an altered fibrin structure. In vitro clot lysis is also increased with all colloids, but there are no reports on augmented in vivo fibrin degradation products. Besides the effect on intraoperative blood coagulation, the hemodynamic effectiveness, duration thereof, effect on microcirculation and edema formation, and, in particular, the effect on the hypercoagulable state in the postoperative period need to be considered in the choice of the replacement fluid during hemodilution and intraoperative blood loss.