24-Hour Indirect Calorimetry in Mechanically Ventilated Critically Ill Patients

Background: Energy imbalance in critically ill, mechanically ventilated patients may lead to medical complications. The nutrition care team needs accurate, noninvasive, rapid methods to estimate energy requirements. We investigated whether brief measurements of indirect calorimetry at any time of the day would give valid estimates of 24-hour energy expenditure (EE). Methods: EE of 12 mechanically ventilated critically ill patients (6 men, 6 women, mean ± SD age 67 ± 18 years, weight 70.2 ± 8.8 kg) was recorded every minute during 24 hours by indirect calorimetry. All patients were continuously fed enteral nutrition. Results: Mean± SD EE was 1658 ± 279 kcal/d (6941 ± 1167 kJ/d). Within patients, EE during the day fluctuated by 234 kcal in the most constant patient to 1190 kcal in the least constant patient, with a mean fluctuation of 521 kcal (12 patients). No statistically significant difference (p = .53) in mean EE between morning (6–12 hours, 1676 kcal), afternoon (12–18 hours, 1642 kcal), evening (18–24 hours, 1658 kcal), and night (0–6 hours, 1655 kcal) was found. A 2-hour instead of a 24-hour measurement resulted in a maximal error of 128 kcal (536 kJ), which was<10% of the average EE. The maximal error decreased with longer time intervals. Conclusions: In mechanically ventilated critically ill patients, 24-hour indirect calorimetry measurements can be replaced by shorter (≥2 hours) measurements. Time of day did not affect EE.