Reconciling divergent results of the latest parenteral nutrition studies in the ICU.

PURPOSE OF REVIEW: Recent studies on the optimal modalities to feed patients during the ICU stay show divergent results. The level and the timing of energy provision is a critical issue, associated with the clinical outcome. These results questioned the clinical relevance of the recent guidelines issued by American, Canadian and European academic societies.

RECENT FINDINGS: Four recent prospective randomized studies enrolled critically ill patients who received various nutritional regimens and tested the effect of nutritional support on outcome. The Tight Calorie balance Control Study (TICACOS) targeted on calorie administration according to measured energy expenditure and found increased ICU morbidity but improved hospital mortality. The large EpaNIC study compared 'early' with 'late' (parenteral nutrition) nutrition, mostly in patients after cardiac surgery, and found an increased morbidity associated with early parenteral nutrition. The supplemental parenteral nutrition (SPN) study randomized the patients after 3 days and targeted the calories administered by parenteral nutrition as a complement to unsuccessful enteral nutrition using indirect calorimetry. The SPN resulted in less nosocomial infections and shorter duration of mechanical ventilation. Finally, a recent Australian study enrolled patients unable to be early fed enterally to receive, or not, parenteral nutrition targeted at 1500 kcal. No complications were noted in the parenteral nutrition group. Lessons from all these studies are summarized and should help in designing better studies and guidelines.

SUMMARY: The critical analysis of recent prospective studies comparing various levels of calorie administration, enteral versus parenteral nutrition and enteral versus SPN confirms the recommendations to avoid underfeeding and overfeeding. Parenteral nutrition, required if enteral feeding is failing, and if adjusted up to a measured optimal level, may improve outcome. More studies on the optimal level of energy and protein administration to optimize the clinical outcome are required to fine tune current guidelines.