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Keywords:

  • pH;
  • PCO2;
  • PO2;
  • bicarbonate;
  • total CO2

Summary

Reasons for performing study: Plastic heparinised vacutainer tubes are used for blood gas analysis in horses. This collection method may not be ideal because influx of atmospheric O2 through the permeable plastic wall of the vacutainer tube and loss of CO2 into the gas phase above the blood sample should increase blood PO2 and decrease PCO2, respectively.

Objectives: To determine the effects of collecting blood into plastic vacutainer tubes and storage conditions on blood gas analysis values.

Methods: Blood was obtained from 6 healthy horses and tonometered at 37°C with 12% O2 and 5% CO2. Three ml aliquots of tonometered blood were collected using a glass syringe or vacutainer tube and stored in iced water or at room temperature for 0, 5, 15, 30, 60 and 120 min. Blood samples from vacutainer tubes were collected aerobically (tube opened for 5 s) or anaerobically (tube remained closed). Blood gas analysis was performed in duplicate using a Radiometer ABL5. Data was analysed using repeated measures analysis of variance and P<0.05 was significant.

Results: Compared to the glass syringe, tonometered blood collected in vacutainer tubes had an immediate, significant, sustained and marked increase in PO2 and an immediate, significant, transient but small decrease in PCO2. Blood PO2 and PCO2 were higher when vacutainer tubes were stored in iced water instead of at room temperature. Measured blood pH and calculated values for plasma bicarbonate and total CO2 concentration and base excess of extracellular fluid were similar when blood was collected in glass syringes or vacutainer tubes and values were not altered by storage temperature or time.

Conclusions: Plastic heparinised vacutainer tubes should not be used to collect samples for measurement of blood PCO2 and PO2. Vacutainer tubes provide an accurate method for measuring plasma bicarbonate concentration, total CO2 concentration and base excess.