Course of measured energy expenditure over the first 10 days of critical illness: A nested prospective study in an adult surgical ICU.

Background & Aims: Various factors may cause significant daily variations in energy expenditure in and between critically patients. This nested, prospective study (ClinicalTrials.gov Identifier: NCT04099108) in a predominantly trauma surgical ICU, aimed to determine the course of measured energy expenditure over the first 10 days of critical illness, and to identify factors contributing to energy expenditure.

Methods: Indirect calorimetry was performed on alternate days from ICU Day 3 ± 1 until Day 10 ± 1. The mean daily measured energy expenditure, respiratory quotient and total energy delivery as a percentage of measured energy expenditure were modelled using linear mixed regression with two fractional polynomial terms to accommodate non-linear responses over time.

Results: Fifty ICU patients (mean age 36.9 ± 11.8 years, Acute Physiology and Chronic Health Evaluation (APACHE II) 13.5 ± 6.6, Sequential Organ Failure Assessment (SOFA) 4.5 ± 3.2) were included. Mean body mass index (BMI) was 24.8 ± 4.0 kg/m and mean ventilation duration 7.7 ± 2.7 days. Mean daily measured energy expenditure showed a significant non-linear response (p = 0.006) increasing over the first 4 days peaking on day 5 and then plateauing. Mean daily respiratory quotient increased over the first 7 days, thereafter plateauing with a slight downward trend from day 8 despite a progressive increase in total energy delivery as a percentage of measured energy expenditure. Mean daily measured energy expenditure was significantly lower in the early than in the late acute phases (p = 0.024), whereas the late- and post-acute phases were similar. Age, sex and BMI significantly influenced measured energy expenditure.

Conclusion: Measured energy expenditure showed a significant non-linear response over the first 10 days in ICU, increasing over the first 4 days peaking on day 5 then plateauing. The observed variability highlights the complexity of managing critically ill patients and the importance of personalised nutrition therapy. Additionally, the observed trend with a peak in measured energy expenditure around day five could inform timing and strategies for nutritional intervention in this patient cohort.