Enteral Tube Feeding
When oral feeding is not possible, the preferred method of nutrition support is the infusion of liquid feeding formulas into the stomach or small bowel (enteral tube feedings). This chapter presents the fundamentals of nutrition support with enteral tube feedings, and will demonstrate how to create a tube feeding regimen for individual patients.
I. General Considerations
A. Trophic Effects
The preference for enteral over parenteral nutrition is based on numerous studies showing that enteral nutrition is associated with fewer infections of bowel origin (1,2,3). This is related to the trophic effects of enteral feeding, summarized in the following statements.
The presence of food or tube feedings in the lumen of the bowel has a trophic effect that preserves the structural integrity of the mucosa (4), and supports the immune defenses in the bowel (such as the production of immunoglobulin A, which blocks the attachment of pathogens to the bowel mucosa) (5).
These trophic effects maintain the barrier function of the bowel, which protects against invasion from enteric pathogens; a phenomenon known as translocation (6).
B. Indications & Contraindications
Patients who are unable to eat and have no contraindications are candidates for enteral tube feeding.
Tube feedings should be started within 24–48 hours of admission to the ICU (1) to take advantage of the protective effects of tube feedings just described. There is evidence that early institution of enteral nutrition is associated with fewer septic complications and a shorter hospital stay (8).
The presence of bowel sounds is not required to initiate enteral tube feedings (1).
Absolute contraindications to enteral tube feedings include complete bowel obstruction, bowel ischemia, ileus, and circulatory shock with high-dose vasopressor requirements (1). Tube feedings can be attempted in stable patients on low doses of vasopressors (1), but any signs of intolerance should prompt immediate cessation of feedings.
C. Trophic vs. Full Feedings
Trophic feedings (10–20 kcal/hr, or up to 500 kcal/day) can be used for the first week in patients who are not malnourished, and are not seriously ill (e.g., postop patients) (1).
For patients who are malnourished or seriously ill, full nutritional support should be achieved within hours of starting tube feedings (1).
II. Feeding Formulas
There are at least 200 enteral feeding formulas that are commercially
available, and the following is a brief description of the different types of feeding formulas. Examples are provided in Tables 37.1, 37.2 and 37.3.
available, and the following is a brief description of the different types of feeding formulas. Examples are provided in Tables 37.1, 37.2 and 37.3.
Table 37.1 Standard, Protein-Enriched, and High-Calorie Feeding Formulas | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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A. Caloric Density
Feeding formulas are available with caloric densities of 1 kcal/mL, 1.5 kcal/mL, and 2 kcal/mL (see Table 37.1). Standard tube feeding regimens use formulas with 1 kcal/mL. High-calorie formulas (2 kcal/mL) are intended for patients with severe physiological stress, and are often used when volume restriction is a priority (9).
1. Nonprotein Calories
The caloric density of feeding formulas includes both protein and nonprotein calories, but daily caloric requirements
should be provided by nonprotein calories. In standard feeding formulas, nonprotein calories account for about 85% of the total calories (see Table 37.1).
should be provided by nonprotein calories. In standard feeding formulas, nonprotein calories account for about 85% of the total calories (see Table 37.1).
2. Osmolality
The osmolality of feeding formulas is determined primarily by the caloric density. Standard feeding formulas with 1 kcal/mL have an osmolality similar to plasma (280–300 mosm/kg). Hypertonic feedings can promote diarrhea, but this risk is minimized by intragastric feeding, where the large volume of gastric secretions attenuates the osmolality.
B. Protein Content
Standard feeding formulas provide 35–40 grams of protein per liter. High-protein formulas provide about 20% more protein than the standard formulas (see Table 37.1), and are typically used to promote wound healing (9).
1. Intact vs. Hydrolyzed Protein
Most enteral formulas contain intact proteins that are broken down into amino acids in the upper GI tract. These are called polymeric formulas.
Feeding formulas are also available that contain small peptides (semi-elemental formulas) and individual amino acids (elemental formulas) that are absorbed more readily than intact protein. These formulas promote water reabsorption from the bowel, and could benefit patients with troublesome diarrhea (unproven). Examples of semi-elemental and elemental formulas include Optimental, Peptamen, Perative, and Vivonex T.E.N.
C. Carbohydrate Content
Carbohydrates (usually polysaccharides) provide 40–70% of the total calories in most feeding formulas. Reduced carbohydrate
formulas, in which carbohydrates provide 30–40% of the calories, are available for diabetics (see Table 37.2); these formulas typically contain fiber.
formulas, in which carbohydrates provide 30–40% of the calories, are available for diabetics (see Table 37.2); these formulas typically contain fiber.
Table 37.2 Selected Fiber-Enriched Feeding Formulas | ||||||||||||||||||||||||||||||||||||||||
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D. Fiber
The term fiber refers to polysaccharides from plants that are not digested by humans. There are two types of fiber: fermentable and nonfermentable.
Fermentable fiber is broken down by gut microbes into short-chain fatty acids, which are an important energy source for the large bowel mucosa (13); i.e., fermentable fiber promotes the viability of the mucosa in the large bowel (1). The uptake of these fatty acids promotes sodium and water absorption, and reduces the water content of stool, which reduces the risk of diarrhea (1).
Nonfermentable fiber is not broken down by gut bacteria. This type of fiber draws water into the bowel, and in-creases the risk of diarrhea.
Selected fiber-enriched feeding formulas are shown in Table 37.2. The fiber in most feeding formulas is a mixture
of fermentable and nonfermentable fiber, so it is no surprise that the effects of mixed-fiber formulas on diarrhea have been inconsistent (1).
The current guidelines on nutrition support recommends the following (1):Related posts:
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