Comparison of Short Term Indirect Calorimetry and Doubly Labeled Water Method for the Assessment of Energy Expenditure in Preterm Infants

Abstract

The accuracy of 8-hour indirect calorimetry (IDC) as an estimate of energy expenditure was investigated in 8 healthy preterm infants (birth weight 1,270 ± 193 g, gestational age 32 ± 3 weeks, mean ± SD) in comparison with an analysis over 5 days using the doubly-labeled water (²H₂¹⁸O) method (DLW). The infants that were fed continuously by nasogastric drip with 120 kcal/kg/day of special infant formula were measured twice under thermoneutral conditions in a closed system indirect calorimeter during 8 h with a 4-day interval; simultaneously isotope decay was measured by isotope ratio mass spectrometry in urine samples collected daily during 5 days from 6 h after an oral dose of 2H2180 on the first day of IDC, all during the 4th postnatal week. The mean differences between carbon dioxide production rate (rCO₂) measured either by single 8-hour IDC or by duplicate 8-hour IDC and the 5-day DLW method, using the two-point analysis or the multipoint analysis were not significantly different from zero. The rCO₂ calculated from the DLW method using the two-point analysis differed ––1.4 ± 1.7% from that measured by the multipoint analysis. The mean differences between the metabolic rate estimated from 8 h of IDC and from the 5-day DLW method based on a measured RQ of 0.90 was ––6.7 ± 6.2% and based on the RQ of the feeding ––4.5 ± 6.0%. These differences were not significantly different from zero. We conclude that IDC over 8 h and two-point DLW measurement over 5 days, both methods that can be applied with relative ease in practice, offer an adequate average estimate of energy expenditure in continuously fed preterm infants under thermoneutral conditions.