[Blood substitutes--current evidence].

The aim to find an artificial substitute for human blood has failed in the past 70 years and will most probably fail in the following future. Genomics, proteomics and posttranslational research have revealed that blood is our most complex and highly coordinated organ. Plasma substitutes can only promote a single function of plasma: the blood volume replacement. The even more complex coordination of the intraerythrocytic hemoglobin functions based on the allosteric structural changes induced by binding of O2, CO2 and NO can not be replaced safely by artificial oxygen carriers. Cell-free haemoglobin binds NO, which under physiological conditions coordinates O2 supply with the respiratory cycle and vasomotor function. The binding of NO to haemoglobin results in hypertonic crisis and in increase of leukocyte adherence and platelet aggregation. These complications may have a fatal outcome.