Dec 222012

Where should we set the dial for caloric delivery to our patients with acute lung injury and acute respiratory distress syndrome (ARDS)? Weak observational trials suggest low caloric intake might be associated with poor outcomes [ref1, 2]. On the other hand, other observational data suggests just the opposite: restricting calories early on may reduce ventilator days or even mortality.[ref3] Full-calorie feedings might increase the risk for aspiration, but underfeeding could result in infections or muscular weakness, as mechanistic examples.

Trophic (trickle) feedings continually stimulate the gut, keeping it healthy and reducing the risk for infection by bacterial translocation. The ARDS Net gang, this time led by Todd Rice of Vanderbilt, asked in the EDEN trial whether trophic feedings or full enteral feedings are preferable for people with ARDS/ALI.

They randomized 1000 patients newly diagnosed with ALI or ARDS, without obvious malnutrition, to receive either trophic feedings (20 kcal/hour) or full enteric feedings (full caloric goal, or ~80 kcal/hour) for 6 days. After that, they all received full enteric feedings, if they were still ventilated.

Despite the full enteric feeding group receiving many more calories (1300 kcal/day vs 400), there were no differences in important clinical outcomes (ventilator-free days at 28 days, 60 day mortality, or infections).

Those receiving full enteric feedings had more gastrointestinal intolerance (vomiting, "high gastric residual volumes," and constipation), although these each occurred on < 5% of feeding days.

A side story: Many of the patients in the trophic feeding group were simultaneously enrolled in the OMEGA trial, testing omega-3 fatty acids vs. control tube feeds in people with ALI/ARDS. Midway through the trial it was clear the omega-3s weren't helping, and might be harming people. The patients receiving omega-3's had more ventilator days, and a strong trend toward a significantly higher mortality. The omega-3 tube feeds were replaced with an isocaloric substitute, and any harmful effects of those omega-3s didn't show up here -- unless, for example, trophic feeds are superior to full enterics, and the harmful omega-3s dragged them down to parity; they don't comment on that possibility here.

Richard Griffith's associated editorial voices the usual reasonable concerns that there weren't enough patients, followed for long enough, to definitively prove there were no adverse sequelae from this short period of trophic feedings for ALI/ARDS patients. He calls for a larger, longer trial, which of course would always be nice. But if there's no effect detectable in 1,000 total patients after 28 days, in a well-conducted trial by the premier U.S. research group in critical illness, how much harder do we have to look before drawing some conclusions?

Clinical Takeaway: Trophic feeding for six days appears likely to be safe and appropriate for people with ARDS/ALI who are not malnourished at baseline. The current recommendations from SCCM and the Canadian Critical Care Society advise full enteric feedings over trophic feedings "whenever feasible" -- we'll watch to see if these recs are revised, in response.

Rice TE and the ARDS Net gang. Initial Trophic vs Full Enteral Feeding in Patients With Acute Lung Injury. JAMA 2012; published online Feb 5, 2012.

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Trophic feeding equal to full enteric feeding in acute lung injury (EDEN trial)