The indirect calorimetry in very low birth weight preterm infants: An easier and reliable procedure

Objectives: Preterm infants are at increased risk of developing extrauterine growth restriction, which is associated with worse health outcomes. The energy needs are not well known, as the measurement of resting energy expenditure (REE) using indirect calorimetry has critical issues when applied to infants. One of the main issues is the time required to obtain reliable data owing to the difficulty in keeping infants quiet during the entire examination. Thus, the aim of this study was to define the minimum duration of calorimetry to obtain reliable data. Methods: The volume of oxygen consumption (VO₂) and the volume of carbon dioxide production (VCO₂) were recorded for a mean duration of 90 consecutive minutes. REE was calculated using a neonatal prototype calculator. We extracted data regarding VO₂, VCO₂, and REE at 10(T1), 20(T2), 30(T3), 40(T4), and 50(T5) minutes of steady state and compared these data to those of entire steady state period. Results: Twenty-six very low birth weight preterm infants were evaluated at 36.58 ± 0.99 wk corrected age. Infants were appropriate for gestational age and clinically stable without comorbidities. There were no significant differences between mean VO₂ and REE at T1 (8.26 ± 1.45 mL/kg to 57.80 ± 10.51 kcal/kg), T2 (8.15 ± 1.41 mL/kg to 56.87 ± 10.05 kcal/kg), T3 (8.04 ± 1.41 mL/kg to 56.32 ± 9.73 kcal/kg), T4 (8.05 ± 1.41 mL/kg to 56.07 ± 10.28 kcal/kg), and T5 (8.06 ± 1.55 mL/kg to 57.17 ± 11.62 kcal/kg), respectively, compared to steady state (8.13 ± 1.33 mL/kg to 56.77 ± 9.34 kcal/kg). The median values of VCO₂ were significantly different only when T1 data were compared with other time slots (7.02 ± 1.02 mL/kg at steady state; 7.26 ± 1.23 mL/kg at T1; 7.13 ± 1.20 mL/kg at T2; 7.02 ± 1.19 mL/kg at T3; 6.85 ± 1.16 mL/kg at T4; 6.91 ± 1.24 mL/kg at T5). Conclusion: Twenty consecutive minutes in steady state condition are sufficient to obtain reliable data on REE in stable, very low birth weight infants.