Background: Platelets (PLT) at room temperature are stored in a gas-permeable PVC bag because of extensive platelet metabolic activity based mainly on O2-dependent mitochondrial oxidative phosphorylation. During cold storage, metabolic activity of PLT is slowed, and lactate production continues at reduced rate. However, the rate of O2 consumption at 4°C, as well as its change over 3 weeks of cold storage, have not been quantified. The minimal O2 concentration necessary to sustain PLT O2 uptake at 4°C is also unknown. We investigated O2 consumption rate of cold-stored PLT by examining an optimized mixture of red blood cells (RBC) and PLT stored in a compatible storage bag that does not allow any gas transmission, using RBC as an O2 reservoir as well as an O2 indicator.
Study
Design/Methods:
Methods:
We obtained PLT apheresis donations on day zero and stored at 4 °C in gas-impermeable bags with polyethylene (PE) blood contact surface. Compatible unit of fresh RBC leukoreduced in AS-1 was made hypoxic/hypocapnic using Hemanext ONE (Hemanext Inc.), O2 content titrated by O2 addition, and then mixed with PLT concentrate at ~1:1 ratio (cell counts). Three starting SO2 values were examined, representing three levels of starting pO2/ total O2 contents. Mixtures were sampled periodically for SO2, pO2, pCO2, pH, total hemoglobin (tHb), and lactate using a cooximeter (measured at 37°C, ABL90 Radiometer). O2 uptake rate was derived from observed net decrease in SO2 between each sampling point and tHb.
Results/Findings:
Results: We accurately quantified O2 consumption rates during cold storage by measuring hemoglobin as an O2 indicator stored at an optimal ratio of RBC to PLT in an O2-impermeable bag. As shown in the Table, PLTs continuously consumed O2 during cold storage as evidenced by steady decrease in RBC’s SO2 down to ~5%SO2. O2 consumption rates were moderately dependent on the starting O2 concentrations (i.e. SO2), and they declined slowly over the storage time. O2 uptake stopped around pO2 ~5mmHg (measured at 37°C). Although the rate decreased gradually over time, it retained ~50% of the initial rate after 3 weeks, suggesting longer survival of mitochondria in PLTs.
Conclusions:
Conclusion: The cold-stored PLTs continued to consume O2 well over 21 days of 4°C storage at a rate over 50% of day 1. Since whole blood has ~20 times higher RBC to PLT ratio compared to the mixture in this study, the results demonstrated unequivocally that the whole blood storage under a typical hypoxic storage condition, while providing known benefits of hypoxically stored RBC, would not limit O2-dependent survival of PLT.
