Enteral Nutrition Support Therapy for Adults
Manual of Clinical Nutrition Management B- 42 Copyright © 2013 Compass Group, Inc.
Method 3: Fluid Balance Method (Grade IV)c
Urine output + 500 mL/dayaHolliday MA, Segar WE. The maintenance need for water in parenteral fluid therapy. Pediatrics. 1957;19:823-832.
bInstitute of Medicine. Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: National Academy
Press; 2004.
cHydration Evidence-Analysis Project. Academy of Nutrition and Dietetics Evidence Analysis Library. Academy of Nutrition and Dietetics;
- Available at: http://www.andevidencelibrary.com. Accessed November 13, 2012.
Approximate Free Watera Content of Nutritional Formulas
Formula mL H 2 O/mL Formula mL H 2 0/kcal
1.0 kcal/mL 0.84 0.84
1.0 kcal/mL with fiber 0.83 0.83
1.5 kcal/mL 0.78 0.52
2.0 kcal/mL 0.71 0.36
aFree water delivered in tube feeding = milliliters of formula delivered milliliters of H 2 O per milliliter of formula
Criteria for Formula Selection (15)
There are a variety of enteral nutrition products on the market, many of which have only subtle differences in
composition. The following criteria should be considered when selecting a formula:
Energy density: An energy density of 1 kcal/mL is considered standard. Additional free water is usually
necessary to meet fluid requirements. Higher energy concentrations (1.5 to 2.0 kcal/mL) may be
indicated when fluid must be restricted or when feeding volumes sufficient to meet energy requirements
cannot be tolerated. Fluid-restricted, energy-dense formulations should be considered for patients with
acute respiratory failure to prevent fluid accumulation and pulmonary edema (5).
Osmolality: Products are available at isotonic osmolalities (300 mOsm/kg), moderate osmolalities (400
mOsm/kg), and high osmolalities (700 mOsm/kg). The main contributors to osmolality are sugars, free
amino acids, and electrolytes. Lipids are isotonic and therefore do not contribute to osmolality. High-
carbohydrate, amino acid–based, or peptide-based formulas have moderate to high osmolality. Formula
osmolality has not been conclusively found to be a direct cause of diarrhea (15).
Protein: Protein sources are intact proteins, peptides, or amino acids. Generally, protein contributes 9%
to 24% of total energy. High-nitrogen formulas may not be well tolerated in patients with certain renal
or hepatic disorders. High-nitrogen concentrations can result in a higher renal solute load and can
predispose elderly patients to dehydration. One gram of nitrogen requires 40 to 60 mL of water for
excretion.
Fat: Fat sources are long-chain triglycerides (LCT) and MCT. The fat content usually ranges from 3% to
35% of energy for amino acid–based or peptide-based formulas and from 25% to 55% of energy for
standard formulas. Fats do not contribute to osmolality. Inclusion of MCT may be beneficial for patients
who experience fat malabsorption or maldigestion, since MCT do not require pancreatic lipase for
absorption, and intraluminal hydrolysis is more rapid and complete than with LCT (15). The MCT do not
supply essential fatty acids, and they may cause complications for cirrhotic patients who have a limited
ability to oxidize MCT. The administration of MCT along with LCT increases the total intestinal
absorption of both types of fats, as compared with the absorption of either fat administered alone.
Carbohydrate: Carbohydrate is the most easily digested and absorbed nutrient. Enzyme digestion is
very efficient, as surface digestion is not rate limiting (except with lactose). The transport process is the
slowest part of carbohydrate metabolism. Carbohydrate sources are monosaccharides, oligosaccharides,
and lactose. The carbohydrate content of formulas ranges from 35% to 90% of energy. Longer
carbohydrate molecules exert less osmotic pressure, taste less sweet, and require more digestion than do
shorter ones. Glucose polymers are better absorbed than free glucose and enhance absorption of
calcium, zinc, and magnesium in the jejunum. Some specialty formulas include fiber, fructose, and/or
fructo-oligosaccharides. Fructo-oligosaccharides occur naturally in a variety of fruits and vegetables and
provide sweetening at a lower cost than sucrose. Fructo-oligosaccharides are poorly absorbed by the
small intestine and fermented in the colon, where they promote the growth of healthy species of bacteria
(15).
Lactose: Lactose is present in milk-based formulas and some blenderized formulas. Most commercial
formulas are lactose free. Due to the presumed high incidence of secondary lactase deficiency in illness,
lactose is not present in most enteral formulas (15).