Early Enteral Feeding Improves Outcome
The constant supply of nutrients to cells is essential for their optimal function and survival. Nutrients supply substrates required for the replication of cells, generation of second messengers, maintenance of cellular barriers, destruction of invading p
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Introduction The constant supply of nutrients to cells is essential for their optimal function and survival. Nutrients supply substrates required for the replication of cells, generation of second messengers, maintenance of cellular barriers, destruction of invading pathogens, and detoxification of oxidants. As such, nutrients are important for wound healing, immune response, muscle contraction, and many other organ functions. It is clear that deprivation of nutrient intake for weeks leads to impaired organ function and death. On the other hand, the effects of short-term nutrient deprivation (lasting a few days) is less clear. Thus, some clinicians routinely starve patients for 5-10 days while others feel that immediate feeding is essential. In this chapter, we review the results of early enteral nutrition (EN) in animal models and human subjects. We summarize with a statement which we believe reflects the current status of early EN.
Experimental Studies Experimental models allow one to evaluate cellular and organ effects of nutrients. These effects provide part of the rationale for early EN.
Gut Blood Flow Postprandial intestinal hyperemia is a locally mediated vasodilatory response to the presence of nutrients in the gut lumen. This vasodilatory response had been known for years [1-5]. In 1910, Brodie et al. [1] demonstrated that the placement of a peptide solution into the lumen of the isolated jejunum resulted in an increase in blood flow and oxygen consumption. Chou et al. [5] studied the effects of various constituents of chyme on intestinal blood flow using isolated loops of canine small intestine. These authors demonstrated that intraluminal placement of digested food resulted in significant increases en jejunal blood flow, whereas instillation of undigested food or pancreatic enzymes alone had no effect. The vasoactive properties of digested food resulted from factors present in the liquid phase (solid and liquid phases of digested food were separated by centrifugation). Addition of bile to diJ.-L. Vincent (ed.), Yearbook of Intensive Care and Emergency Medicine 1997 © Springer-Verlag Berlin Heidelberg 1997
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gested food enhanced its hyperemic effect, while bile alone had no effect. These results indicate that it is the water soluble endproducts of food digestion that are responsible for increasing intestinal blood flow. Bile serves to solubilize the lipid nutrients. When individual nutrients were studied for their vasoactive properties, it was found that glucose increased jejunal blood flow [5-7]. The long chain fatty acid, oleic acid, and the monoglyceride mono-olein had no effect on intestinal blood flow. However, solubilization of these lipids by increasing pH, adding bile or sodium taurocholate resulted in increased intestinal blood flow by 20-30% [5-8]. It appears that micellar lipids are very potent dilators of the intestinal vasculature. The triglyceride triolein had no effect on intestinal blood flow, even when bile was present. At physiologic concentrations,
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