Estimating energy expenditure in critically ill adults and children

Designing effective nutrition support regimens for critically ill patients requires an understanding of the energy needs of each patient. Many disease processes result in elevated caloric requirements, whereas some clinical procedures and medications may diminish the metabolic response. Experienced clinicians are unable to predict the extent to which trauma or injury will affect energy requirements for an individual. Both under- and overfeeding a critically ill patient may prolong hospitalization and increase morbidity and mortality. Applying equations that were originally developed for healthy nonhospitalized individuals to predict the energy requirements of critically ill patients will often result in significant errors and may lead to provision of inappropriate nutritional support. The measurement of resting energy expenditure by indirect calorimetry is a valuable tool and can be used to predict energy requirements for most spontaneously breathing critically ill patients, but may lead to spurious results in mechanically ventilated pediatric patients. In the complex and rapidly changing context of critical illness, individualized assessment of energy requirements is crucial. Whichever technique is used initially to assess energy requirements, sequential monitoring and constant reassessment of each patient is essential to provide the appropriate nutritional care regimen. The purpose of this article is to review the equations for estimating and the techniques, practical aspects, and interpretation of measuring energy expenditure in critically ill patients.