Maintaining mucosal immunity during parenteral feeding with surrogates to enteral nutrition

Pneumonia and intra-abdominal abscesses are significantly lower in trauma patients receiving enteral feeding compared with those receiving parenteral feeding. Extensive experimental evidence suggests that this is related to maintenance of the mucosal-associated lymphoid tissue, which provides immunologic protection for both the gastrointestinal and respiratory tracts against microbial flora and infectious pathogens. This system is exquisitely sensitive to the route and type of nutrition delivery that affects its functional effectiveness. Although parenteral nutrition decreases the effectiveness of this extraintestinal mucosal immunity, specialty nutrients like glutamine and neuropeptides such as gastrin-releasing peptide and cholecystokinin are capable of preventing some of the immune defects associated with parenteral nutrition. This review examines the mechanisms associated with the mucosal immunity and role of both glutamine and neuropeptides in normalizing defects induced by parenteral feeding. Based upon evolving data, specific nutrients and products of the enteric nervous system show promise as adjuncts to parenteral feeding that are capable of maintaining immune function in patients unable to be fed via the gastrointestinal tract.