Indirect calorimetry: methodology, instruments and clinical application.
OBJECTIVE
This review aims to identify the basic methods for accurately measuring a patient's energy expenditure in clinical nutrition practice by indirect calorimetry, and the impact upon a disease state of applying the results obtained.


RESULTS
The open-circuit method is the most widely used in the majority of classical instruments for measuring energy consumption. Advances in gas exchange measurement have made this technique readily and precisely available at the bedside. Nevertheless, it is important to understand its intricate primary methodology for safe and correct application. The stress and activity factors should be carefully and specifically applied, and the respiratory quotient abandoned, for tailoring a patient's daily nutrition regimens. Caloric expenditure measured by indirect calorimetry coupled with the doubly labeled water technique introduced the concept of physical activity energy expenditure, which added to resting energy expenditure results in total daily energy expenditure. Compact modular and handheld devices have been introduced into the market, together with similar technology for evaluating exercise energy expenditure, making utilization easier, safer and precise. In the critically ill population, which is exposed to medical and surgical interventions, indirect calorimetry has greatly changed the practice of caloric administration, significantly reducing the total daily amount.


CONCLUSIONS
In conclusion, one has to be careful when choosing devices, and understanding and clinically applying the results obtained by indirect calorimetry, bearing in mind that measured resting energy expenditure should be the daily caloric goal in order to diminish clinical morbidity.
da Rocha
Eduardo E Moreira
EE
NUTROCLIN, Clínica São Vicente/Gávea, Rio de Janeiro, Brazil. edurocha46@globo.com
Alves
Valéria Girard F
VG
da Fonseca
Rosana Barcellos V
RB
D002153:Calorimetry, Indirect / Q000295:instrumentation* / Q000379:methods* / Q000592:standards; D016638:Critical Illness; D002149:Energy Intake / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology*; D006801:Humans; D009751:Nutritional Requirements; D011659:Pulmonary Gas Exchange; D012449:Safety; D012680:Sensitivity and Specificity