PLATELET METABOLISM DURING STORAGE OF PLATELET CONCENTRATES AT 22-DEGREES-C

Abstract

The development of methods for storing [human] platelet concentrates (PC) at 22.degree. C for transfusion was predominantly empiric, with minimal knowledge of metabolic events occurring during storage. A decrease in pH due to accelerated production of lactic acid in hypoxic conditions apparently is a major cause for loss of platelet viability. Metabolic parameters such as O2 and glucose consumption rates and CO2 and lactic acid production rates were measured. The O2 and CO2 transport capacities of various containers and the buffering capacity of plasma were measured. The O2 consumption rate was 1.10 .+-. 0.16 (SD) nmol/min per 109 platelets. In well-oxygenated systems, lactic acid formation was 1.74 .+-. 0.12 nmol/min per ml PC for PC with a platelet count of 1 to 2 .times. 109/ml; and 0.52 mol of glucose was consumed/1 mol lactic acid produced. In a completely O2-free system, lactic acid production increased 5- to 8-fold. Of energy generation, 85% is derived through oxidative metabolism and glucose may not be the primary substrate for this metabolism. Bicarbonate concentration, initially 22.1 .+-. 1.6 meq/l, decreased 1.41 .+-. 0.18 meq/min per ml PC for PC with counts 1 to 2 .times. 109 platelets/ml. The loss of bicarbonate was caused by displacement by lactic acid and as a consequence of spontaneous CO2 efflux from the container. CO2 production, 2.3 .+-. 0.4 nmol/min per 109 platelets, was derived from O2 consumption and the CO2 liberated from bicarbonate as it was consumed. A rapid fall in pH to levels below 7.0 (22.degree. C) took place when the bicarbonate concentration fell below 5 meq/l as lactate concentrations reached 20-25 mmol/l. A further increase in lactate concentration from 25 mmol/l-40 mmol/l correlated with a further fall in pH to 5.8. The ultimate storage life of a PC is determined by continuous lactate production and the fixed buffering capacity of plasma and by the glucose concentration of the PC. With knowledge of these parameters, methods for predicting pH as a function of time, platelet count, and O2 and CO2 transport capability of the container were developed as guidelines for future work.