Stability of PO2, PCO2, and pH in fresh blood samples stored in a plastic syringe with low heparin in relation to various blood-gas and hematological parameters.

Objective: To assess the stability of PO2, PCO2 and pH in fresh individual blood samples drawn in a plastic syringe with low heparin and stored at 22 degrees C or on ice in relation to various biochemical and hematological parameters of the samples.
Methods: PO2, PCO2, and pH were measured at determined times in samples kept at 22 degrees C or on ice. The magnitude of change in blood-gas parameters over time for each group of samples was determined. The change in PO2 was examined according to its initial value, the oxygen content (CaO2), the hemoglobin concentration, the leukocyte and platelet counts of each sample.
Results: The changes in PO2, PCO2, and pH over time were about three times lower in samples stored on ice than in the ones at 22 degrees C. Nevertheless, rapid increases in PO2 were observed for samples stored on ice with an initial PO2 between 50 and 250 mm Hg. Samples with PO2 over 250 mmHg exhibited a decrease in PO2 over time. No correlation was observed between the change in PO2 and the oxygen content, the hemoglobin concentration or the leukocyte and platelet counts for both groups of samples stored at 22 degrees C or on ice.
Conclusion: PO2 in samples with an initial PO2 between 50 and 250 mm Hg stored on ice should be analyzed within 30 min. However, PCO2 and pH didn't exhibit clinically significant changes within 60 min under similar conditions. The magnitude of change in PO2 for samples kept on ice was dependent on their hemoglobin capacity for buffering oxygen, which is in converse relation with the oxygen saturation level of hemoglobin (SatHbO2). It is believed that the alteration in PO2 for samples stored on ice is produced predominantly by diffusion of oxygen through the plastic wall of the syringe, whereas it would be mainly of metabolic origin in samples at room temperature.