Characterization of HCO3−/CO2 Pool Sizes and Kinetics in Infants

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Abstract
The 1st bicarbonate pool sizes and kinetic data necessary for the interpretation of substrate oxidation studies were determined in 6 fed, nonacidotic infants, ages 2.5-5 mo. Following an i.v. bolus of NaH13CO3 (50 .mu.mol/kg), breath samples were collected over 240 min for the analysis of breath 13CO2. Each breath 13CO2 disappearance curve was fitted to a multicompartmental bicarbonate model previously derived in adults. The mean sizes of the 3 bicarbonate pools were: 7.4 .+-. 0.8 mmol/kg (central pool), 15.1 .+-. 4.8 mmol/kg (rapidly exchanging peripheral pool) and 8.8 .+-. 3.5 mmol/kg (slowly exchanging peripheral pool). The mean percentage dose recovery was 57 .+-. 10%. The pool sizes suggested that extensive metabolic exchange of carbon between HCO3- and organic metabolites occurred in the infant.