Energy Expenditure Under General Anesthesia - An Observational Study Using Indirect Calorimetry in Patients Having Noncardiac Surgery

BACKGROUND: Perioperative hemodynamic management aims to optimize organ perfusion pressure and blood flow-assuming this ensures that oxygen delivery meets cellular metabolic needs. Cellular metabolic needs are reflected by energy expenditure. A better understanding of energy expenditure under general anesthesia could help tailor perioperative hemodynamic management to actual demands. We thus sought to assess energy expenditure under general anesthesia. Our primary hypothesis was that energy expenditure under general anesthesia is lower than preoperative awake resting energy expenditure.

METHODS: We conducted an observational study on patients having elective noncardiac surgery at the University Medical Center Hamburg-Eppendorf (Germany) between September 2019 and March 2020. We assessed preoperative awake resting energy expenditure, energy expenditure under general anesthesia, and energy expenditure after surgery using indirect calorimetry. We compared energy expenditure under general anesthesia at incision to preoperative awake resting energy expenditure using a Wilcoxon signed-rank test for paired measurements.

RESULTS: We analyzed 60 patients. Median (95% confidence interval [CI]) preoperative awake resting energy expenditure was 953 (95% CI, 906-962) kcal d-1 m-2. Median energy expenditure under general anesthesia was 680 (95% CI, 642-711) kcal d-1 m-2-and thus 263 (95% CI, 223-307) kcal d-1 m-2 or 27% (95% CI, 23%-30%) lower than preoperative awake resting energy expenditure (P < .001).

CONCLUSIONS: Median energy expenditure under general anesthesia is about one-quarter lower than preoperative awake resting energy expenditure in patients having noncardiac surgery.