Tuy nhiên, nó không phải là rõ ràng cho dù đó là thực sự mang lại lợi ích cho có tự do hemoglobin với ái lực oxy gần bình thường. Có thể tưởng tượng được rằng phản ứng nhanh chóng của oxy với hemoglobin miễn phí như trái ngược với hemoglobin trong các tế bào hồng cầu có thể bù đắp những ảnh hưởng của một mối quan hệ ôxy tăng lên. | Artificial Blood Components 113 Some of them are common to all or a group of HBOCs while others are specific for one product. As nowadays all tested hemoglobin solutions use highly purified hemoglobin theoretically stroma viruses and endotoxins are not a concern. oxygen affinity Most natural free hemoglobin molecules have a high oxygen affinity. To change their affinity to more normal values hemoglobin has been modified. Pyridoxylation adding pyridoxal-5-phosphate 13 orcross-linking . by3 5-dibromosalicylate 14 increases the oxygen affinity of hemoglobin. The cross-linker o-raffinose modifies the 2 3-DPG pocket of the hemoglobin resulting in a higher P50. However it is not clear whether it is really beneficial to have free hemoglobin with an oxygen affinity near to normal. It is thinkable that the more rapid reaction of oxygen with free hemoglobin as opposed to hemoglobin in the red cell may offset the effects of an increased oxygen affinity. A higher oxygen affinity may ensure that the microcirculation is not unduly affected by high oxygen levels. oncotic effects Red cell transfusions per se do not exert relevant oncotic pressure. In contrast free hemoglobin does. This is a two-edged sword. To draw fluids from tissues into the circulation plasma expansion may be beneficial in hemorrhaging patients or in patients with ischemia due to tissue swelling. However in cases where additional intravascular fluids are detrimental the oncotic effects of HBOCs may be harmful. The extent of the oncotic effects encountered depends on the number not on the size of the particles. Therefore many small particles as in intramolecularly crosslinked hemoglobins exert a much greater oncotic pressure than fewer yet bigger particles with the same amount of hemoglobin as in LEH . rheological properties viscosity A circulating viscous fluid in the vessels exerts a shear stress on the vessel wall. This results in the release of NO a vasodilator. By this mechanism whole human blood with a
