P Nutr Soc
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Review Meta Analysis
Glutamine in critical care: current evidence from systematic reviews.
Glutamine, the most abundant amino acid in the body, is thought to become conditionally essential in critical illness. Some of the important roles for glutamine are as a carrier for inter-organ N, a preferred fuel for enterocytes and cells of the immune system, a substrate for renal NH3 formation and a precursor for glutathione. ⋯ Trials of parenteral nutrition containing glutamine with patients after elective surgery also suggest reduction of infection, but it is unlikely that glutamine-containing parenteral nutrition would be used for such patients. The evidence base is limited by the quality of the reported trials and the suggestion that there is publication bias, with trials suggesting reduced infection being more likely to be published.
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Critically-ill patients experience an extent of hyperinflammation, cellular immune dysfunction, oxidative stress and mitochondrial dysfunction. Supplementation with key nutrients, such as glutamine and antioxidants, is most likely to have a favourable effect on these physiological derangements, leading to an improvement in clinical outcomes. The results of two meta-analyses suggest that glutamine and antioxidants may be associated with improved survival. ⋯ A novel design feature is the combined use of parenteral and enteral study nutrients dissociated from the nutrition support. The therapeutic strategies tested in the randomized trial may lead to less morbidity and improved survival in critically-ill patients. The trial will be conducted in approximately twenty tertiary-care ICU in Canada and the first results are expected in 2009.
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During critical illness free radical production may increase as a result of, for example, sepsis or tissue trauma. In addition, because of a potential for increased losses, and the possibility of inadequate nutrition, the antioxidant defences of the body may become compromised. ⋯ Various nutritional and pharmacological strategies to enhance antioxidant defences have been proposed, which aim either to maintain or enhance endogenous antioxidant stores or to provide alternative antioxidant agents. Trace elements and amino acids are particularly important, and their synergistic role in the maintenance of the body's antioxidant defence network will be discussed.
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Excessive or inappropriate inflammation and immunosuppression are components of the response to surgery, trauma, injury and infection in some individuals and can lead, progressively, to sepsis and septic shock. The hyperinflammation is characterised by the production of inflammatory cytokines, arachidonic acid-derived eicosanoids and other inflammatory mediators, while the immunosuppression is characterised by impairment of antigen presentation and of T-helper lymphocyte type-1 responses. Long-chain n-3 fatty acids from fish oil decrease the production of inflammatory cytokines and eicosanoids. ⋯ As a consequence, an emerging application for n-3 fatty acids, in which they may be added to parenteral (or enteral) formulas, is in surgical or critically-ill patients. Parenteral nutrition that includes n-3 fatty acids appears to preserve immune function better than standard formulas and appears to diminish the extent of the inflammatory response. Studies to date are suggestive of clinical benefits from these approaches, especially in patients post surgery, although evidence of clinical benefit in patients with sepsis is emerging.