The acidosis-induced right shift of the HbO2 dissociation curve is maintained during erythrocyte storage

Abstract

Background and objectives. In fresh blood, tissue hypoxia increases microcirculatory acidosis, which enhances erythrocyte O2 unloading and increases the amount of available O2. Storage of erythrocytes increases the HbO2 affinity and reduces O2 unloading. We examined the development of the affinity change during a period of 5 weeks of storage by present blood bank standards, and investigated to what extent acidosis offsets the affinity change. Materials and methods. Blood from volunteer donors was processed and stored as erythrocyte concentrates (EC). At 2–5 day intervals, EC were drawn from the bags and suspended in plasma and crystalloids to an Hb ≈ 10 g/dL. The suspensions were adjusted to give a pH of 7.40, 7.10, 6.80 or 6.30 and equilibrated with different gas mixtures to SO2 0, 25, 50, 75 and 100%. Measurements of the PO2/SO2 pairs at each pH were used to calculate the position of the HbO2 curve and its P50 value. Results. A significant leftward shift in the HbO2 curve was established after 1 week of storage; after 2.5 weeks only minor further changes were observed. Acidification right-shifted the HbO2 curve, after 2.5 weeks of storage the curve at pH 7.10 was similar to that for fresh blood at pH 7.40. Calculations of extractable O2 showed that the left-shifted HbO2 curve of stored EC could be advantageous at a low arterial PO2. Conclusions. The rightward shift of the HbO2 curve due to acidosis is well maintained in stored erythrocytes, a moderate pH decrease offsets the storage-induced increased HbO2 affinity.