Energy Needs Are Poorly Predicted in Critically Ill Elderly

Changes in energy expenditure with age have been described, but this physiology is not routinely considered when managing critically ill elderly patients. To allow us to avoid the potential problems associated with underfeeding or overfeeding the critically ill elderly population, with approval of the human studies committee and appropriate consent from legal guardians, 25 critically ill patients over 65 years of age requiring mechanical ventilation underwent expired gas indirect calorimetry. If they had a pulmonary artery catheter in place for clinical reasons, reverse-Fick indirect calorimetry was also performed. Data obtained by indirect calorimetry was compared with commonly applied equations for predicting energy expenditure by statistical methods of correlation and limits of agreement. These 25 patients had an average age of 74 ± 1.23 (standard error of the mean) and an average APACHE II score of 15. Predictive equations correlated poorly with measured resting energy expenditure, and although they showed reasonable bias, they were imprecise in their estimation of resting energy expenditure. These data suggest that energy expenditure in critically ill, mechanically ventilated elderly patients is highly variable. Although generally overestimating energy needs, currently available equations for predicting energy expenditure in this population are associated with significant bias and imprecision, which may lead to both overfeeding and underfeeding. Although these equations may be suitable as a basis of initiating nutritional support, energy provisions should ideally be guided by indirect calorimetry.