The age of stored erythrocytes influences methaemoglobin formation when circulated in a heart-lung machine model.

The formation of storage lesions, which is caused especially by oxidative stress, is a well-known process associated with prolonged storage of erythrocytes1–3. However, its relevance for patients receiving a transfusion is still under discussion4,5. Erythrocyte concentrates are frequently required by patients managed with extracorporeal circulatory systems, such as a heart-lung machine (HLM), extracorporeal life support, extracorporeal membrane oxygenation or other circulatory support techniques. It was reported that the survival of patients was negatively influenced the longer erythrocyte concentrates were stored at 4 °C prior to transfusion, for example, after heart surgery6,7. However, the studies that reached this conclusion, especially the retrospective one6, were intensely criticised and some other retrospective and prospective studies were not able to show significant differences in outcomes (multiple organ dysfunction score, decrease of 90-day mortality) following transfusion of fresh or older blood8,9. Nevertheless, less pronounced effects cannot be excluded. Red cell concentrates seem to be stable to some extent during storage at 4 °C, since the rate of haemolysis is normally below 1% before transfusion. This is, however, obviously only a semi-stable condition, since with increasing storage times, an average of 25% of transfused erythrocytes may disappear from the circulation10. The very considerable temperature increase from 4 °C to 37 °C and the mechanical stress during circulation in the patient are great challenges to transfused erythrocytes. These effects may be even more pronounced if the patient needs extracorporeal circulation, because of the huge area of artificial surfaces and mechanical damage from blood pumps11. The influence of artificial surfaces on corpuscular blood components as well as the activation or inhibition of different haemostatic parameters can be investigated effectively in a closed system, such as the model of extracorporeal circulation used in our study. One advantage of using such a model is that the patient’s autogenic regulation, which may attempt to equalise the effects caused by extracorporeal circulation, can be excluded. The aim of this study was to investigate the influence of extracorporeal circulation on various parameters of erythrocytes that had been stored at 4 °C for different periods of time (6, 20, and 34 days after blood donation), using a HLM model at 37 °C. Samples were taken at the beginning and after 2, 4 and 6 hours of circulation. The most significant change observed was a rapid increase in methaemoglobin (MetHb) concentration during circulation. Since the formation of MetHb is associated with the generation of reactive oxygen species (ROS), we further investigated whether the inclusion of suitable antioxidant substances could initially inhibit lipid peroxidation in a model system using erythrocyte ghosts.