COMPARISON OF MEASURED CARBON-DIOXIDE PRODUCTION WITH THAT OBTAINED BY THE ISOTOPE-DILUTION TECHNIQUE IN NEONATAL PIGS - OBSERVATIONS ONSITE OF INFUSION

Fifteen newborn pigs (1.5 kg) were used to estimate CO2 "production" over a 5-h experiment. In each piglet, the average expired air CO2 irreversible loss rate measured over 15-min intervals was compared with an estimate Of CO2 "produced" by a continuous infusion of (NaHCO3)-C-14 into either the aortic artery (seven pigs) or the portal vein (eight pigs). The specific radioactivity (Bq/mumol) of the expired CO2 taken over consecutive 15-min intervals during the 5-h period was fitted to an exponential model to predict the specific radioactivity at steady state. This specific radioactivity was used to calculate the total CO2 irreversible loss rate and to correct for the difference in tracer infused in relation to tracer excreted at 5 h (76 to 78%). The estimated CO2 "produced" tended to be higher (P < 0.12) when the aortal rather than the portal infusion site was used [571 vs. 498 mumol/(min.kg0.75)]. The isotope dilution technique significantly (P < 0.05) overestimated the expired air CO2 regardless of whether the aortal 1571 vs. 469 mumol/min kg0.75)] or portal 1498 vs. 447 mumol/(min.kg0.75)] routes of infusion were used.