HEALTHY ADULTS HAVE A CLOSELY INTERRELATED NUtritional, metabolic, and immune system that regulates food requirements and responds well to short-term nutritional deprivation but not to nutrient excess. However, when critically ill, patients no longer have control over their food intake, and clinicians may administer nutritional support with little understanding of individual patient needs in the light of inflammatory demands, injury responses, and the underlying influences of genotype and age. Because robust evidence about the nutritional requirements for critically ill patients at the various stages of their illness is lacking, particularly when they are acutely ill, clinicians often base nutritional support on “requirements” based on averages and guesswork. Nutritional support in excess of actual requirements may contribute to metabolic stress. In the intensive care unit (ICU), parenteral nutrition can facilitate excessive early provision of nutrients during a period of considerable uncertainty about requirements. This was illustrated in the study by Casaer et al, in which very early targeting of full feeding requirements with parenteral nutrition in the first few days was not beneficial. The authors of that study suggested the possibility that nutrition might suppress the normal activation of acute mechanisms necessary to remove cellular damage. In patients receiving mechanical ventilation, enteral feeding rarely delivers consistently more than 80% of the target full feeding, but it is still reasonable to question whether further restriction of enteral nutrition would be preferable during the early stages of an acute illness. Inthis issueof JAMA,Riceandcolleagues,writingfor theNational Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome (ARDS) Clinical Trials Network, report findings examining whether there is any advantage to restricting the amount of initial enteral intake among mechanically ventilated patients with acute lung injury (ALI). The EDEN study was a large, unblinded trial from 44 sites that recruited 1000 patientssoonafterstartingventilationanddevelopingALI(about 80% of which was attributable to primary pneumonias or sepsis). The study hypothesis was that administration of considerably reduced, trophic feeding (about 25% of the target full feeding) during the first 6 days would increase ventilator-free days(VFDs)comparedwithamoreactivelyadvancedconventional full enteral nutrition regimen achieving a target target intakeof80%.Thishypothesiswasnot supportedby thestudy findings: there was no difference between trophic feedings vs full enteral feedings in VFDs or any important secondary end points, includingICUstay,organfailure–freedays,28-daymortality, and 60-day mortality. Nonetheless, this study highlights several important practical points. The majority of these patients can be fed nasogastrically; the majority tolerate gastric residual volumes of 400 mL, measured at 6-hour intervals, without high rates of aspiration or increased ventilator-associated pneumonia; and using a protocolized approach for feeding allows clinicians to deliver a greater volume of the target feeding amounts than prior groups have reported. One potentially confounding factor was that the study was initially combined in a factorial design with another study, the OMEGA trial, which randomized patients to receive a supplement containing omega-3 fatty acids, -linolenic acid, and antioxidants until stopped for futility after 272 patients (27%) had been recruited. The results of the trial by Rice et al cannot be used to conclude that trophic feeding is equivalent to full feeding in critically ill patients. This study was not designed or powered as an equivalence study and does not provide definitive data to informcliniciansabouthowmuchnutritionalsupportisenough, how early it should be started, or even if there should be “no nutritionprovision”intheinitialphaseofcritical illness—acase that has been persistently argued and remains to be tested. The effect of nutrition on an end point such as VFDs does not simply depend on dose and duration but on several other factors. These may include a complex interaction of prior nutritional reserves; the effects of any initial or evolving nutritional deficiency; the extent and severity of the underlying illnesses; the processes of recovery interacting with the metabolic signaling and stress from the nutrients; and the burdens imposed by the complications of providing nutritional support. These factors suggest that not all patients may benefit equally. An important challenge is identifying patients at increased nutritional risk.
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Feb 7, 2012
Julie A Bastarache + 4
Open Access
