Local and systemic factors lead to an increase in inflammatory cell infiltration of the burn wound with removal of damaged tissue in preparation for epithelialization and wound healing. The cytokine cascade precipitated by stress hormones in response to injury involves tumor necrosis factor-a (TNF-a), which subsequently activates leucocyte production of IL-1, IL-6, platelet-derived growth factor, and eicosanoids (prostaglandins, thromboxanes, and leu-kotrienes). These in turn amplify the cellular and cytokine responses by release of chemotactic factors. TNF-a and the cytokines are also mediators of the increased metabolic and catabolic response seen in burns patients. TNF-a will increase acute-phase protein synthesis and increase loss of amino acids from skeletal muscle. However, it is also associated with the healing process in that wound healing is stimulated as a result of vascular proliferation and collagen synthesis. Excessive release of TNF-a can be harmful and is associated with muscle wasting, excessive weight loss, increased nitrogen loss, systemic inflammatory response syndrome, and debility.
These early immune reactions give way, in the second and third week postburn, to injury immuno-suppression. This takes the form of reduced responsiveness of lymphocytes, impaired production of IL-2, and changes in immune cell phenotypes. Burn injury inhibits the T-helper 1 response but promotes a T-helper 2 response. As a result, IL-2 and interferon^ (IFN-7) production is reduced, which increases the risk of infection. Membrane lipid composition also influences lymphocyte and macrophage functions in terms of signaling and eicosaniod production. There is a reduction in n-6 (mainly arachi-donic) fatty acids and an increase in PGE2, which can lead to immunosuppression. Dietary replacement of n-6 by n-3 polyunsaturated fatty acids (PUFAs) reduces immunosuppression by altering membrane composition and eicosanoid series production. Nutritional studies have focused on the influence that enteral feed composition has on immune function—so-called immune-enhancing diets. The theoretical elements of interest are n-3 PUFAs and the amino acids arginine and glutamine. The evidence base for a clinically measurable advantage of such immune-enhancing preparations is yet to be fully established. Small studies have shown a reduction in wound infection rate and a possible reduction in length of stay per percentage total body surface area burned.
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