Energy expenditure and oxygen consumption under general anaesthesia: a single-center observational study using indirect calorimetry in patients having elective non-cardiac surgery.

Abstract

Perioperative hemodynamic goal-directed therapy is an important tool to optimise perioperative end organ oxygen delivery and prevent perioperative morbidity, especially in high-risk patients. To improve hemodynamic goal-directed therapy, there is a need for an individualised, patient centred approach. Most protocols of perioperative hemodynamic goal-directed therapy focus on the monitoring and optimisation of oxygen delivery and cardiac output. However, at times in the perioperative period, cellular metabolic needs cannot be fulfilled even if oxygen delivery is adequate. Cellular metabolic needs are reflected by energy expenditure. Thus, perioperative energy expenditure could give better guidance about the actual individual cellular metabolic needs of the patient. By monitoring perioperative energy expenditure, unfulfilled cellular metabolic needs could be detected where actual hemodynamic monitoring would not detect a need for intervention. Still, perioperative energy expenditure has yet scarcely been described. In this single-center observational study, we measured perioperative energy expenditure and oxygen consumption, which is mathematically and physiologically coupled with energy expenditure, in 60 patients undergoing elective non-cardiac surgery. Our patient population includes patients of different age and surgical intervention, representing our modern patient population. We measured energy expenditure and oxygen consumption using the gold standard, indirect calorimetry. All patients were measured preoperatively while awake, under general anaesthesia, and postoperatively within the first 24 hours after the end of surgery. Additionally, on an exploratory basis, we measured intraoperative energy expenditure and oxygen consumption in 20 patients undergoing abdominal surgery. In our study, energy expenditure decreased by 26% and oxygen consumption by 27% under general anaesthesia, compared to preoperative awake values. Postoperative values showed no difference to preoperative awake values. Overall intraoperative energy expenditure and oxygen consumption in the abdominal surgery group did not exceed preoperative values. Perioperative measuring of energy expenditure using indirect calorimetry is feasible. It remains to understand how perioperative energy expenditure should be interpreted and which interventions should be used to respond to the measured values. Further studies are needed with set hemodynamic monitoring and goal-directed therapy protocols to expand today’s knowledge about perioperative energy expenditure.