Recovery of labeled CO₂ from acetate in severely burned children

The purpose of this study was to determine the fractional recovery rate of labeled CO₂ in the breath of severely burned children. This information is needed to perform tracer studies of substrate oxidation using carbon-labeled fatty acids. Nine children, ages 4-14 yr with massive burns participated in the study. All experiments were performed 7 days post burn after an overnight fast. A primed (60 μmol/kg), constant (2.0 μmol· kg^-1min^-1) infusion of [1,2-¹³C]acetate was given during a 4-h basal period and during a 4-h hyperinsulinemic euglycemic clamp. A priming dose (150 μmol/kg) of NaH¹³CO₃ was given at the beginning of the study. Breath samples were collected every 10 min during the last 40 min of each period. Indirect calorimetry was performed during the last 30 min of each period. The isotopic enrichment of 13CO2 was determined by isotope ratio-mass spectrometry, and total CO2 excretion was measured by indirect calorimetry. The fractional recovery of acetate label was 0.89 ± 0.05 and 0.88 ± 0.04 during the basal state and clamp, respectively. We conclude that the fractional recovery of labeled acetate in severely burned children is approximately three times the recovery of a nonburned adult and similar to the value in exercising adults. The high recovery rate reflects the rapid turnover of the TCA cycle in burned children relative to the rate of exchange reactions. Minimal correction of expired CO₂ data is needed in this circumstance to quantify fatty acid oxidation using ¹³C- labeled fatty acids.