Feeding critically ill patients: what is the optimal amount of energy?

Hypermetabolism and malnourishment are common in the intensive care unit. Malnutrition is associated with increased morbidity and mortality, and most intensive care unit patients receive specialized nutrition therapy to attenuate the effects of malnourishment. However, the optimal amount of energy to deliver is unknown, with some studies suggesting that full calorie feeding improves clinical outcomes but other studies concluding that caloric intake may not be important in determining outcome. In this narrative review, we discuss the studies of critically ill patients that examine the relationship between dose of nutrition and clinically important outcomes. Observational studies suggest that achieving targeted caloric intake might not be necessary since provision of approximately 25% to 66% of goal calories may be sufficient. Randomized controlled trials comparing early aggressive use of enteral nutrition compared with delayed, less aggressive use of enteral nutrition suggest that providing increased calories with early, aggressive enteral nutrition is associated with improved clinical outcomes. However, energy provision with parenteral nutrition, either instead of or supplemental to enteral nutrition, does not offer additional benefits. In summary, the optimal amount of calories to provide critically ill patients is unclear given the limitations of the existing data. However, evidence suggests that improving adequacy of enteral nutrition by moving intake closer to goal calories might be associated with a clinical benefit. There is no role for supplemental parenteral nutrition to increase caloric delivery in the early phase of critical illness. Further high-quality evidence from randomized trials investigating the optimal amount of energy intake in intensive care unit patients is needed.