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Everyone agrees that providing adequate nutrition in critical illness is vitally important. The problem is, no one knows for sure what “adequate” means.
Caloric targets are not based on evidence from randomized trials with meaningful clinical outcomes. They emerge as consensus from educated guesses by researchers conducting physiology studies. One camp believes that extra calories should be provided to counteract catabolism; another argues that illness-induced anorexia is adaptive and that a normal caloric load represents overfeeding.
When caloric goals during critical illness have been tested in randomized trials, no advantage has been shown for providing a “normal" calorie diet vs. restricting calories:
- In ARDS, trophic (trickle) tube feedings appeared equal to full enteric feedings, in EDEN and this trial;
- Early parenteral nutrition to achieve "normal" caloric goals resulted in greater morbidity than underfeeding for 7 days in patients unable to take enteral feedings;
- In severe acute pancreatitis, providing nutrition within 24 hours brought no advantage over providing no nutrition for 3 days.
Most experts agree that protein should be provided in abundant amounts (>1 g/kg/day) to counteract catabolism of critical illness, regardless of the total calories delivered. There are experimental data and observational studies to support this belief.
Add to this thicket of equipoise the new PermiT trial in the New England Journal of Medicine.
Investigators at 7 centers in Saudi Arabia, Canada, and Lebanon randomized 894 critically ill patients requiring mechanical ventilation with diverse diagnoses to receive enteral feedings totaling either 40-60% of calculated caloric needs, or 70-100%. All patients were targeted to receive 1.2-1.5 g/kg of protein. Parenteral nutrition was rarely used (<1% of total calories in the study).
Patients were on-protocol for their entire ICU stay up to 14 days (or until they could eat), after which their physicians could provide nutrition ad hoc. Patients in the restricted-calories group received 46% of their caloric targets, on average, compared to 71% of goal for the full-calorie arm.
There was no difference in mortality at 90 days (27% vs 29%), or any other outcome (organ failure, ventilator-free days, infections, dialysis need, mortality in the hospital, at 28 days, or at 6 months).
Clinical Takeaway: This study echoes the consistent signal shown by numerous randomized trials testing nutrition in the early phase of critical illness: total calories provided does not affect clinical outcome. Early initiation of parenteral nutrition (before 7 days) might be harmful compared to permissive underfeeding. This new trial further supports the overall safety of a low-calorie approach to nutrition in critical illness, as long as adequate protein (a target >1.2 g/kg/day here) is provided.
Arabi YM et al. Permissive Underfeeding or Standard Enteral Feeding in Critically Ill Adults. N Engl J Med 2015; published online.