Storage changes of blood

Loss of red cell viability is the most important practical consideration. Progressive loss of viability varies according to the anticoagulant used. The time limit for storage of blood is set taking this into consideration. After transfusion of stored red cells, a proportion are removed from the circulation within the first 24 h. The remainder appear to survive normally. With increased length of storage, a greater proportion of red cells are

Optimal additive solution (OAS, e.g. SAG-M)

Optimal additive solution (OAS, e.g. SAG-M)

First centrifugation |Red cells in OAS_| Second centrifugation

Figure 16.1 Diagrammatic representation of the preparation of components from whole blood by the 'top and bottom' or 'buffy coat' method. Items in boxes represent final components. FFP, fresh-frozen plasma.

Whole Blood Components

Cells washed through under gravity to empty pack

Cells washed through under gravity to empty pack

Buffy coat pool

Centrifuge

Centrifuge

Figure 16.2 Preparation of leucodepleted pooled, buffy coat-derived platelet preparations. PAS, platelet additive solution; LD, leucodepletion.

removed within the first 24 h. The destruction at 24 h of more than 30% of the total number of cells transfused is considered unacceptable.

Depletion of ATP is progressive during storage of red cells, leading to changes in red cell shape (discs to spheres, loss of membrane lipid and increased rigidity). These changes can be partially reversed by incubation with purine nucleosides, and reduced by addition of adenine at the time of collection. ATP seems to be an important determinant of red cell viability, although not the only one.

Reduction in red cell 2,3-DPG during storage is less severe in CPD blood than in ACD: 2,3-DPG levels are normal in CPD and CPD-AI blood at 1 week. Reduced red cell 2,3-DPG levels increase the oxygen affinity of Hb, and the oxygen dissociation curve is shifted to the left, with less oxygen being given up to the tissues. The red cell 2,3-DPG level is restored to normal by approximately 24 h post transfusion. The clinical significance of the low 2,3-DPG level of stored red cells is only likely to be an important consideration in recipients with severe anaemia or coronary artery insufficiency. Even in massive transfusion of stored blood, depletion of red cell 2,3-DPG can probably be well tolerated if cardiac function is satisfactory.

Electrolyte changes are the result of equilibration of sodium and potassium levels across the cell membrane once active trans port has been halted by the cooling of blood to 4°C. There is rapid restoration of electrolyte levels after transfusion.

The pH of blood decreases rapidly with storage, but most recipients can handle the acid load during transfusion without ill effect.

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