29-29: Enteral Nutritional Support Solutions

Patients who require enteral nutritional support in an acute care setting receive commercially prepared enteral formulas (Table 29–3). Most enteral formulations have been designed to provide adequate proportions of water, energy, protein, and micronutrients. Some formulas contain less free water for patients who require fluid restrictions. Modular products are also available to provide specific macronutrients (eg, protein, carbohydrate, and fat) to supplement commercially available formulas for patients with unique nutrition requirements.

Enteral formulas can generally be classified as standard (polymeric), peptide-based (elemental or semi-elemental) or disease-specific. The classification is generally based on the overall composition of the formula and its contained macronutrients. Most enteral formulas are lactose-free.

Standard polymeric formulas are generally isotonic, have moderate amounts of intact macronutrients and may contain fiber. Normal digestive and absorptive capacity are needed for the use of polymeric formulas. Isotonic formulas contain 1 kcal/mL, whereas concentrated formulas contain 1.2–2 kcal/mL. Standard polymeric formulas are well tolerated in most patients.

Semi-elemental and elemental formulas are designed for patients with impaired GI function who have demonstrated malabsorption and maldigestion with standard polymeric formulas. Elemental formulas contain free amino acids, whereas semi-elemental formulas contain partially hydrolyzed oligopeptides. Elemental formulas contain minimal amounts of fat, typically in the form of medium chain triglycerides, which can increase the risk of EFAD when used long term in patients. Elemental formulas are hypertonic and can result in severe diarrhea.

Disease-specific enteral formulas have been designed for patients with diabetes, kidney disease, hepatic encephalopathy, and respiratory failure. However, they have not been shown to be superior to standard polymeric formulas for most patients.