Effect of tracer infusion site on measurement of bicarbonate-carbon dioxide metabolism in dogs

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Abstract
Ten dogs were given a primed infusion of H13CO3- for 220 min while under general anesthesia. Isotopic steady state was reached within 60 min in exhaled CO2, femoral arterial blood HCO3- and femoral venous blood HCO3-. Halfway through each infusion study, the site of tracer infusion was changed either from the central aorta to a peripheral vein, or vice versa. The mean HCO3--CO2 flux measured from blood HCO3- enrichments was 15.7 .+-. 2.1 (SD) mmol .cntdot. kg-1 .cntdot. h-1. The mean fraction of tracer recovered in exhaled CO2 was 79 .+-. 7% (SD) of the infused dose. No significant difference in either HCO3- flux or recovery of tracer was found between the venous and arterial infusions of tracer. These results indicate that when venous administration of HCO3- tracer is compared with central arterial infusion, the initial loss of tracer into expired CO2 is an unimportant consideration in experiments measuring HCO3- kinetics.