Loss of carbon dioxide from serum samples exposed to air. Effect on blood gas parameters and strong ions.
BACKGROUND
The acid-base status of patients is frequently inferred from the concentration of total carbon dioxide in a venous blood sample. Prior studies of hemodialysis patients have reported lower values for tCO(2) when blood is shipped to a distant central laboratory compared to samples assayed at a local laboratory. Loss of tCO(2) from the sample after exposure of the blood to room air was postulated as the predominant factor.


METHODS
Serum samples were assayed on-site before and at varying intervals after removing the tube stopper on an AVL OPTI Critical care Analyzer using E-Cl cuvettes.


RESULTS
A rapid and progressive decline in pCO(2) and increase in pH was documented over a 2 h period. However, the change in tCO(2) during this time period was small and not significant. There were no changes in the concentrations of strong ions.


CONCLUSIONS
The discrepancy in tCO(2) reported previously cannot be attributed solely to rapid loss of CO(2) unless assay conditions greatly enhance the rate of loss compared to the experimental conditions used in this study.
Kirschbaum
Barry
B
Department of Medicine, Division of Nephrology, Medical College of Virginia, Virginia Commonwealth University, P.O. Box 980160, Richmond, VA 23298, USA. bkirschb@hsc.vcu.edu
D000136:Acid-Base Equilibrium; D000138:Acidosis / Q000097:blood; D001784:Blood Gas Analysis; D002138:Calibration; D002245:Carbon Dioxide / Q000097:blood*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006435:Renal Dialysis
D002245:Carbon Dioxide