Physiology of Blood Storage.
Blood storage is extremely significant process in medical field. It attempts to bring the potentially life-saving benefits of transfusion to the patients who need them by making blood components available, safe and successful. The volume of a unit of blood is approximately 1 pint (450-500 mL). Units of blood collected from donors are separated into multiple components, such as packed red blood cells, platelets, and plasma.
The units are collected either as whole blood into bags containing anticoagulant citrate and nutrient phosphate and dextrose (CPD) or by aphaeresis into acid citrate dextrose (ACD). For better long term preservation of blood cells and for transfusion purpose citrate is used in combination with dextrose in the following form:
a. Acid- Citrate- Dextrose (ACD) solution: Trisodium citrate, citric acid and dextrose solution is used. Its PH is 5.4. For use, 10 volumes of blood is added to 1.5 volumes of solution.
b. Citrate-Phosphate : Dextrose-Adenine(CPD-A) Solution: trisodium citrate, citric acid dextrose and adenine solution is used. Its PH is 5.6-5.8. For use 7 volumes of blood is added to 1 volume of solutions .
Dextrose helps in liberating lactic acid which decreases the PH resulting in survival of RBCs both in vitro and in vivo. It also provides a substrate for the metabolism, which is still required even at 4˚C and thus helps in cell survival. Under such condition blood can be stored for 14 days. 80% cells survive for 24 hrs after transfusion and thereafter surviving cells are destroyed at a rate of 1% per Day.
Stored blood is not a suitable medium for transfusing WBC and platelets to a recipient because blood stored for longer than 24 hrs contains virtually no viable WBCs and platelets. Cold storage decreases cell metabolism. It decreases active transport and cations move with concentration gradient. Therefore cell loses K+ ions increasing plasma k+ concentration from 4-5 mEq/L to 20-30 mEq/L in 2 weeks and gains Na+ which increases intra cellular Na+ concentration from 12mEq/L to 30-40 mEq/L. The loss of K+ and gain of Na+ cause net increase in cell total base and water, as a result cells become shorter and more spherocytic. This causes increase in their hemolysis in hypnotic solution and cell may rupture in vitro even in 0.8% NaCl solution. If stored cells are transfused, they become normal in less than 48hrs, with reference to Na+ and K+ content, volume, shape and saline fragility.
text book of Physiology , Vol-1, Prof. A.K. Jain