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Blood transfusion is the key life-saving treatment in many traumatic emergencies, chronic or acute pathologies, and during or upon surgical interventions. The primary goal of blood transfusion is the fast recovery of oxygen delivery to organs, especially the brain. Furthermore, circulation volume is restored, thus maintaining the blood pressure at levels that guarantee an efficient blood flux. Whereas this secondary need can be fulfilled to some extent by blood expanders, such as colloid- and crystalloid-based solutions, up to now no approved alternative to red cells is available for oxygen supply. The main transfusion active principle, red blood cells, is derived from the voluntary action of blood donors. Transfusions can be and are considered a very safe and effective oxygen-based therapy, provided that detailed guidelines are followed1. This evaluation has been somewhat challenged in recent years2–5. Presently, clinical studies are underway to provide a more solid ground to the safety and efficacy of blood transfusions (examples available at: http: //clinicaltrials. gov/ct2/show/type: clinical-trial, attrs: {text: NCT01038557, termᵢd: NCT01038557}NCT01038557 and http: //clinicaltrialsfeeds. org/clinical-trials/show/type: clinical-trial, attrs: {text: NCT00991341, termᵢd: NCT00991341}NCT00991341). Indeed, transfusions are exposed to a series of limitations, listed in table I, that can lead to potential health risks. For example, in stored blood the intracellular levels of the haemoglobin allosteric effector 2–3 bisphosphoglycerate (2, 3-BPG), that maintains the p50 (the oxygen pressure at 50% saturation) in vivo at 26 torr, decreases in one week from 5 mM to negligible concentrations, resulting in a drop of the p50 to about 12 torr3. The concentration of potassium ions in red cells increases from 4 mM in fresh blood to about 20 mM after three weeks of aging3. In the same time range, lactate concentration increases from about 1 to 15 mM, and solfohaemoglobin (HbSO2) from 30% to almost 100%. The intracellular pH of red cells drops from 7. 4 to 6. 9 in a few hours and to a value of 6. 7 in three weeks3. Furthermore, free haemoglobin, i. e. haemoglobin released due to red cell haemolysis, increases from 5 μM at 3 hours after blood withdrawal to about 20 μM after three weeks3. Free haemoglobin scavenges nitric oxide (NO), the molecule that controls vessel tone, and undergoes oxidation, leading to pro-oxidative radical-based reactions6. Studies on blood units aging have also pointed to adverse effects associated to the decreased capability of red cell haemoglobin to supply nitric oxide4. However, this is a controversial issue7, 8.
Mozzarelli et al. (Tue,) studied this question.