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Very little evidence guides nutrition in critical illness. Because of critically ill patients' catabolic state, and probably influenced by the normalization fallacy, nutrition practices often include efforts to provide daily calories in the 1,800 - 2,000 range.
However, anorexia may be adaptive during illness (since it is common to multiple disease states); greater enterally infused volumes could precipitate gastric aspiration; and excess calories could generate oxidative stress.
Randomized trials have suggested that giving far fewer calories than "normal" is appropriate and safe for most patients with severe critical illness. A huge new trial from ANZICS in Australasia further bolsters this paradigm.
Investigators in Australia and New Zealand randomized almost 4,000 patients receiving mechanical ventilation to either 1 kcal/mL or 1.5 kcal/ml enteral feedings. Target infusion rate was 1 mL/kg ideal body weight / hour (i.e., 60-70 ml/hour on average). Most patients received enteral nutrition within one day of enrollment, for about one week total, at 80% of their target rates. Patients with significant burns were excluded.
Because of the difference in caloric density, the standard 1 kcal/ml group received only 1,262 calories/day, while the high-calorie 1.5 kcal/ml group received 1,863 calories/day.
There were no differences in the primary outcome (death within 90 days), nor other endpoints (ventilator days, time in the ICU and hospital, organ failure, or infections).
However, the group receiving high-density feedings did worse on clinically important parameters, experiencing:
- Higher need for insulin
- More emesis
- Higher gastric residuals
- Receipt of more promotility drugs
Since volumes infused were roughly equal between groups, the hyperglycemia and reduced gut motility were apparently directly caused by the higher caloric content of the feedings. It would be hard to imagine a clearer message to us from the gut brain telling us not to overfeed critically ill patients.
The TARGET trial joins the EDEN trial, along with a randomized trial in 2011 and one in 2015 in an enlarging canon of research strongly suggesting that targeting "normal" caloric goals in severely critically ill patients should not be considered normal at all.