The adaptational mechanism in acute normovolemic hemodilution with long-lasting colloids is basically an increased flow rate to organs and tissues due to decreased viscous flow resistance. There is no decrease in systemic oxygen transport and no increase in oxygen extraction ratio unless the hematocrit drops well below 20%. Thus adequate tissue oxygen supply is guaranteed in limited hemodilution as shown by direct measurements of tissue PO₂. The feasibility of the new concept of acute preoperative hemodilution with subsequent autotransfusion of the shed blood has been demonstrated in a number of clinical studies. Within the safe limits of clinical dilution in the hematocrit range of 25-20% adequate tissue oxygenation is provided by a rise in cardiac output, whereas heart rate, blood gases and acid base status are essentially unchanged. Autotransfusion during and after surgery helps to save donor blood, is easy to perform, gives better tissue perfusion at the microcirculatory level and prevents postoperative thromboembolic complications.

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