title: Energy expenditure measurements in ventilated critically ill children: within- and between-day variability.
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%.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Children's Nutrition Research Centre, Royal Children's Hospital, Department of Paediatrics and Child Health, University of Queensland, Herston, QLD, Australia.
authors.forename: M S
authors.initials: MS
authors.lastname: White
authors.forename: R W
authors.initials: RW
authors.lastname: Shepherd
authors.forename: J A
authors.initials: JA
authors.lastname: McEniery
mesh_terms: D000293:Adolescent; D002153:Calorimetry, Indirect; D002648:Child; D002675:Child, Preschool; D002940:Circadian Rhythm; D016638:Critical Illness; D002149:Energy Intake; D004734:Energy Metabolism; D004750:Enteral Nutrition; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D010288:Parenteral Nutrition; D012121:Respiration, Artificial