Effects of Syringe Material, Sample Storage Time, and Temperature on Blood Gases and Oxygen Saturation in Arterialized Human Blood Samples

BACKGROUND: The practice of on-ice storage of arterial-blood samples in plastic syringes for delayed analysis continues, and the effects of storage time and temperature on the measurement of blood-oxygen-saturation values (S_aO2) have not been adequately described.

OBJECTIVE: To determine the effects of syringe material, storage time, and storage temperature on normal arterialized blood gas and S_aO2 values.

METHODS: We used a temperature-controlled extracorporeal circuit to “arterialize” 500 mL of fresh, whole human blood at 37°C, and we used certified calibration gases of 12% O₂ and 5% CO₂ to produce normal blood-gas values. From that arterialized blood we took 90 samples and randomly assigned them to 6 groups, until there were 15 samples in each group. The groups were (1) plastic syringe, analyzed immediately, (2) plastic syringe, stored 30 min at 0-4°C, (3) plastic syringe, stored 30 min at 22°C, (4) glass syringe, analyzed immediately, (5) glass syringe, stored 30 min at 0-4°C, and (6) glass syringe, stored 30 min at 22°C.

RESULTS: Compared to the samples that were analyzed immediately, the P_O2 of the samples stored in plastic syringes for 30 min at 22°C and at 0–4°C was significantly higher, with a clinically important magnitude of 11.9-13.7 mm Hg. The P_CO2 of blood stored in glass for 30 min at 0-4°C was significantly lower, although the magnitude of the difference (1.5 mm Hg) was not clinically important. There were no statistically significant differences in pH or oxygen saturation among the 6 groups.

CONCLUSION: For accurate arterial-blood-gas results, samples drawn in plastic syringes should be analyzed immediately. If the analysis is going to be delayed, the samples should be drawn and stored in glass.