[Hemodilution]

Haemodilution is a familiar therapeutic procedure known as phlebotomy since the days of ancient Greece. Animal experiments and epidemiological data offer favourable results for the use of haemodilution in cases of ischaemic stroke. As a matter of principle, both the cerebral blood flow and cerebral microcirculation can be improved by lowering the haematocrit. However, the effectiveness of haemodilution has as yet not been sufficiently validated by clinical studies. Results obtained to date are controversial. In all probability, the effectiveness of haemodilution depends on the type of stroke, thus rendering a pathogenetic differentiation of cerebral strokes a prerequisite for the relevance of such studies on haemodilution. Additionally, the haemorheological and microcirculatory mechanisms of haemodilution are probably more complex than generally assumed up to now. Therefore, lowering the haematocrit does not automatically improve the microcirculation. In addition, the other haemorheological parameters, such as erythrocyte aggregation, plasma viscosity and erythrocyte deformability, must be taken into consideration.