Nutritional influence on the recovery of 14CO2 in critically ill trauma patients

Several factors, including age, nutritional and metabolic status, and underlying pathological conditions, should be considered in estimating the correction factor for labeled CO2 retention. We have evaluated the nutritional influence of this correction factor in a group of severely injured (injury severity score = 33 +/- 5), hypermetabolic, and highly catabolic adult trauma patients. Primed-constant infusion of NaH14CO3 was used, and the breath 14CO2 radioactivity was measured. The experiment was conducted once in the fasting condition during the early catabolic "flow" phase of injury and again during and after a week of intravenous feeding. The mean value of the 14CO2 recovery (85.2 +/- 2.7%) in the basal fasting condition was higher than the value of 81% commonly used in normal subjects. During intravenous nutritional support the recovery was 100.8 +/- 1.7%. Recovery of tracer increased linearly with O2 uptake and CO2 production. The linear expression obtained between recovery and CO2 production could estimate the recovery within 3% in trauma patients, and that obtained by multiple regression with CO2 production and O2 uptake would predict the recovery within 1.5%.