Upon completion of the chapter, the reader will be able to:
Discuss how gut structure and function impact choice of feeding route and outcome of feeding.
Estimate kilocalorie and protein requirements of an enteral feeding candidate and design an enteral nutrition (EN) regimen to meet these.
Evaluate patient-specific parameters to determine whether EN is appropriate.
Compare clinical efficacy, complications, and costs of EN versus parenteral nutrition (PN).
Formulate a monitoring plan for an EN patient.
Select appropriate medication administration techniques for an EN patient.
Enteral nutrition (EN) is broadly defined as delivery of nutrients via the gastrointestinal (GI) tract. The terms enteral nutrition and tube feedings are often used synonymously. Formulas for EN usually are delivered in the form of commercially prepared liquid preparations, although some products are produced as powders for reconstitution, and a few patients may be appropriate for delivering specific blenderized foods down their feeding tubes.1 Nonvolitional feedings in patients who cannot meet nutritional requirements by oral intake include EN and parenteral nutrition (PN), which are collectively known as specialized nutrition support (SNS).
Several organizations have issued clinical guidelines on the use of EN. These include the American Society for Parenteral and Enteral Nutrition (ASPEN), European Society for Clinical Nutrition and Metabolism (ESPEN), and a Canadian team known as Critical Care Nutrition.2–5 ASPEN and the Society for Critical Care Medicine (SCCM) have jointly issued guidelines for SNS in critically ill patients.6
GI TRACT STRUCTURE AND FUNCTION
Anatomy and Absorptive Function
With normal volitional feeding, food is ingested via the mouth. There, the process of breaking down complex foodstuffs into simpler forms that can be absorbed by the small bowel begins. Solid food is chewed in the mouth, and enzymes begin digestion. Presence of food in specific regions of the GI tract triggers release for many enzymes and GI hormones. Food is swallowed and passes through the esophagus and the esophageal sphincter to the stomach, where additional digestive enzymes and acids further break it down. The stomach also mixes and grinds.
The food, now in a liquid form known as chyme, passes through the pyloric sphincter into the duodenum, where stomach acid is neutralized. The food then passes from the duodenum into the jejunum, where most absorption of digested carbohydrate and protein occurs. Most fat absorption occurs within the jejunum and ileum, the final segment of the small bowel. In the small bowel, breakdown of carbohydrate, protein, and fat occurs both within the lumen and at the intestinal mucosal membrane surface. The absorptive units on the intestinal mucosal membrane are infoldings known as villi. These villi are made up of epithelial cells called enterocytes. Projections from these enterocytes called microvilli increase surface area of the small bowel and make up the brush-border membrane.