Dynamic Metabolic Changes Measured by Indirect Calorimetry

The energy expenditure (EE) of critically ill patients varies throughout the course of the disease. It is influenced by numerous individual and iatrogenic factors, as well as different metabolic phases. Therefore, measuring EE may be beneficial in mitigating the detrimental effects of undernutrition or overnutrition. Consequently, all recent societal guidelines recommend the use of Indirect Calorimetry (IC) to determine energy needs in mechanically ventilated patients. IC allows for the measurement of the actual energy expenditure of the patient, facilitating individualized metabolic support and preventing side effects associated with artificial nutrition in the three phases: early acute phase, late acute phase, and recovery phase, during which metabolism undergoes significant variations. The present chapter will explore the dynamic nature of energy expenditure (EE) in critically ill patients and its correlation with the progression of the disease. The focus is on how IC enables the precise measurement of the patient’s actual energy expenditure, facilitating the implementation of tailored metabolic support.