<Li> Interface with a Ventilator (Intensive Care settings): In case the patient is mechanically ventilated, an indirect calorimeter can still measure breath by breath inhaled / exhaled O and CO if interfaced with the ventilator through the endotracheal tube . </Li> <P> Indirect calorimetry provides at least two pieces of information: a measure of energy expenditure or 24 - hour caloric requirements as reflected by the Resting Energy Expenditure (REE) and a measure of substrate utilization as reflected in the Respiratory Quotient (RQ). Knowledge of the many factors that affect these values has led to a much broader range of applications . Studies of indirect calorimetry over the past 20 years have led to the characterization of the hypermetabolic stress response to injury and the design of nutritional regimens whose substrates are most efficiently assimilated in different disease processes and organ failure states . Indirect calorimetry has influenced everyday practices of medical and surgical care, such as the warming of burn unit and surgical suites and the weaning of patients from ventilators . </P>

Indirect calorimetry works based on the principle that