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Stored Blood...Are we treating or just rising Hct



First click on this link to see a video on the effect of blood transfusion on Microcirculation
                                                            
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One of the characteristic alterations in stored RBC is a change in shape from a normal biconcave to a spindly cell (echinocyte).(1)

This results in lower surface to volume ratio, spherocytosis, increased cell Hb concentration and viscosity, increased osmotic fragility.(1)

Osmotic fragility will cause release of Hb, long known as a potent scavenger of the vasodilator NO, recently shown to constrict vessel and therefore reduce blood flow at levels as low as 0·01 g/dl .(3)

Recent studies show a role for the RBC beyond that of an oxygen carrier. Haemoglobin in the red cell can act as an oxygen sensor during hypoxia, enabling the RBC to regulate blood flow releasing the vasodilators nitric oxide (NO) and adenosine triphosphate (ATP). Storage of RBC could impair their hypoxic vasodilator release(2)

Thus Fresh blood transfusion is more effective in relieving effects of microcirculatory hypoxia. Banked blood, in particular 2-week stored blood, has limited capacity of improving tissue oxygenation.(4)

However Blood transfusions still are effective in improving tissue oxygenation better than fluids even if old blood is used given this is leuco-depleted.Moreover threre is some evidence that Blood transfusions provide oxygen carrying RBC to the microcirculation by recruiting empty capillaries (⇓diffusion distance) but not by increasing flow.(5)


Refrences:

1-Beutler E, Kuhl W, West C: The osmotic fragility of erythrocytes after prolonged liquid storage and after reinfusion.

Blood 1982; 59:1141–1147


2-Ellsworth ML: The red blood cell as an oxygen sensor: what is the evidence?
Acta Physiol Scand

3-Jia L, Bonaventura C, Bonaventura J, Stamler JS: S-nitrosohaemoglobin:a dynamic activity of blood involved in vascular control.
Nature

4-Reiter CD, Wang X, Tanus-Santos JE, Hogg N, Cannon RO, III, Schechter AN, Gladwin MT: Cell-free hemoglobin limits nitric oxide bioavailability in sickle-cell disease.

5-Effects of fresh versus banked blood transfusions on microcirculatory hemodynamics and tissue oxygenation in the rat cremaster model. Gonzalez AM, Yazici I, Kusza K, Siemionow M. Surgery. 2007 May;141(5):630-9

6-Blood transfusions recruit the microcirculation during cardiac surgery
Transfusion. 2011 May;51(5):961-7.
Nat Med 2002; 8:1383–13891996; 380 :221–2262000; 168 :551–559
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