A simple method to calculate oxygen consumption (VO2) and CO2 production (VCO2) over a 24-h period is described. VO2 and VCO2 were measured using flow-through technique and the total VO2 and VCO2 over a given period of time were determined from the area under the O2 and CO2 concentration-time curve of the mixed expired gas. The system was tested in vitro by burning 100% ethyl alcohol. The average error between measured and theoretical values for VO2 was 4.9% and for VCO2 was 4.7%. With a flow rate greater than 5340 ml/min through the system, the correlation coefficient between theoretical VO2 or VCO2 and measured VO2 or VCO2 was 0.99. The method was tested in vivo in 5 premature infants who were nursed under neutral thermal environment and received routine medical care. The results indicate that this simple method can be used to study the total and interim changes of daily VO2 and VCO2 in infants during their ongoing nursery care.
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