Can 2-hour Indirect Calorimetry Measurement Accurately Predict 24-hour Energy Expenditure in Critically Ill Surgical Patients?

Abstract Background Measuring energy expenditure (EE) by indirect calorimetry (IC) has become the gold standard tool for critically ill patients in order to define energy targets and tailor nutrition. Debate remains as to the optimal duration of measurements, or the optimal time of day in which to perform IC. Methods In this retrospective observational study, we analyzed results of daily continuous IC in 270 mechanically ventilated, critically ill patients, admitted to the surgical intensive care unit (SICU) in a tertiary medical center, and compared measurements performed at different hours of the day. Results A total of 51,448 IC hours was recorded, with an average 24-hour EE of 1523 ± 443 kcal/day. Night shift (00:00–8:00) was found to have a significantly lower EE measurements (mean 1498 kcal/day, 95% CI 1445–1551), than afternoon (16:00–00:00, mean 1526 kcal/day 95% CI 1473–1577) and morning (8:00–16:00, mean 1539 kcal/day, 95% CI 1483–1594) measurements (p < 0.001 for all). The bihourly time frame which most closely resembled the daily mean was 18:00–19:59, with a mean of 1523 ± 434 kcal/day. Daily EE measurements of the continuous IC at days 3–7 of admission showed a trend towards a daily increase in 24-hour EE, but the difference was not statistically significant (p = 0.077). Conclusions Periodic measurements of EE can differ slightly when performed in various hours of the day, but the error range is small and may not necessarily have a clinical impact. When continuous IC is not available, a 2-hour EE measurement between 18:00–19:59 can serve as a reasonable alternative.