Energy Expenditure Measurements in Ventilated Critically III Children: Within‐ and Between‐Day Variability

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Abstract
Background: Energy expenditure measurement (EEM) by indirect calorimetry is used as a research and clinical tool in pediatric intensive care units. The aims of the study were to determine if a 30‐minute EEM is representative of a 24‐hour EEM (within‐day variation); to determine if there is any diurnal variation during the 24‐hour period of EEM; and to determine if there is a clinically significant between day variation of EEMs. Methods: To determine within‐day variation, energy expenditure was measured for a period of 24 hours for each subject (n = 11). The 24‐hour period was then divided into 30‐minute periods. The 30‐minute means were compared with the 24‐hour means. To determine between‐day variation, EEMs were made daily for 30 minutes. Results: In the within‐day study, the overall mean percent coefficient of variation of the 30‐minute measurements was 7.2% ± 4.5%. There was no significant difference between the 30‐minute means and the 24‐hour means for each patient (p <.691). In 8 subjects the 30‐minute means did not differ from the 24‐hour mean by more than 20%. No diurnal variation was observed. The mean percent variation of between day EEM was 21% ± 16%; the range was 1% to 69%. Conclusion: In critically ill ventilated children, clinically relevant within‐day variations in EEM are uncommon and a single 30‐minute EEM gives an acceptable guide to the level of nutrition support required. Between‐day variations can, however, be large and daily EEMs are required. (Journal of Parenteral and Enteral Nutrition 23:300–304, 1999)