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Enteral Nutrition - Choice of Enteral Feeds and Substrates Used

The Choice of enteral feeds would depend on GI function, volume restrictions, patient’s bowel habits and specific dietary restrictions or needs. In general with a normally functioning GI tract and no other encumbrances, most patients will tolerate a standard whole protein feed containing soluble fibre. Constipated patients may benefits from feeds containing insoluble fibre. It is also important to remember that the inside diameters of many feeding tubes are small and can be easily blocked. Feeds given by such tubes should therefore be non-viscous and free of non-soluble particles. All feeds should contain optimal macro and micronutrients.


Presently a wide variety of ready-to-use commercially prepared diets are available in the market, which meet the above requirements. However, ready-to-use feeds are expensive and in our country we still prefer to use blenderized home made diets. Homemade diets, of course have their disadvantages; they have a low caloric density requiring large volumes of liquids and are usually thick and likely to clog the tube. Hence, close monitoring of fluid intake and careful rinsing of the tubes with water after every feed is essential. Appendix B- [Table d] lists the common sources of nutrients used in liquid homemade diets.


In selecting commercial feeding formulae, one should be familiar with their characteristics and composition, For instance, patients whose daily energy requirements are high or those who are volume restricted, can be given high caloric density formulae (1.5 to 2 kcal/ml) [Table 1]. In most cases density is determined primarily by the carbohydrate content, which also determines the osmolarity of the compound. Hence, the high caloric density formulae also have the highest osmolarities (>1000 mOsm/L) and are markedly hypertonic to body fluids which can induce diarrhea. Most formulae provide approximately 35 to 40 gm of protein content. Most enteral formulae provide intact proteins (polymeric) that are broken down to aminoacids. Such peptide base formulations can be used in patients with impaired intestinal absorption. These formulae also promote water reabsorption from the bowel and can be beneficial in patients with severe diarrhea [Table 1].


Though lipids provide the maximum calories, excessive fat ingestion is not well tolerated and causes diarrhea. Hence, the lipid content of most formulae is limited to 30% of the total calories. Nonetheless, lipid-rich formulae are available which provides 55% of total calories through fats thereby replacing carbohydrates as the main source of energy. These formulae are used in patients with respiratory failure with CO₂ retention, because in this group of patients, carbohydrates increase further CO₂ production and metabolic load. Certain enriched formulae containing glutamine or dietary fibre are also available [Table 2]. Gultamine supplementation helps in maintaining the functional integrity of bowel mucosa and glutamine stores decline precipitously in acute hypercatabolic states. Hence, glutamine fortified formulae help In providing an essential nutrient in hypermetabolic stressed patients. Dietary fibre in the feed may reduce the tendency to watery diarrhea. However, one should focus on prevention and treatment of the cause of the diarrhea as mentioned in the complications of enteral nutrition.


Table 1

Polymeric and oligometric formulae: Sources of Nutrients and Energy content

Nutrient
Polymeric Formula
Oligomeric Formula
Protein content
30-80 g/l
20-50 g/l
Sources of Protein
Caseinate, sou protein isolate, delactosed lactalbumin, beef, egg albumin, egg white, low fat milk
Casein hydrolysate, soy bean protein hydrolysate, free aminoacids
Carbohydrate Content
90-200 g/l
100-200 g/l
Source of Carbohydrate
Maltodextrin, glucose polymers, sucrose, glucose, fructose
Maltodextrin, glucose polymers, sucrose, glucose, fructose
Fat Content
20-90 g/l
5-20 g/l
Sources of Fat
Soybean oil (LCT*),
Corn Oil, canola oil,
Sunflower oil,
Safflower oil,
Coconut oil (MCT**)
Soybean oil (LCT*),
Corn Oil, canola oil,
Sunflower oil,
Safflower oil,
Coconut oil (MCT**)
Caloric Density
1 to 2 Kcal/l
1 to 1.7 Kcal/l

*LCT: Long Chain Triglycerides, **MCT: Medium Chain Triglycerides


Table 2

Available enteral formulae:

A) Standard formulae
1 Kcal/ml calorie density Approximately 35-40 g/L of protein Average 300-500 mOsmol/L osmolarity
B) Enteral formulae with high calorie density
1.5 to 2 Kcal/ml calorie density Approximately 40-45 g/L of protein Average 600-700 mOsmol/L osmolarity
C) Special Formulae
Benefits
High lipid content, 55%
Limits nutrition induced CO₂ retention in respiratory failure
Containing arginine, RNA and fatty acids derived from fish soil
Enhances immune function
Containing a carotene and fatty acids derived from Fish soil
Limits inflammatory mediated tissue injury
Glutamine enriched feeding formulae
May prevent bacterial translocation and provides mucosal gut integrity
Fiber enriched feeding formulae
Reduce tendency of diarrhea and serves as metabolic support for mucosa of large intestine.

It is worth mentioning that many critically ill patients do not necessarily require expensive and special commercial preparations. For instance, we have fed many of our patients with extensive burns with a simple blenderized diet (Butter Milk Diet – BMD)


BUTTER MILK DIET (BMD)

1000 ml butter milk + 4 eggs + 4 bananas + 10 tablespoons of sugar

Final composition of the above is approximately 1700 ml and it provides 1 kcal/ml of energy, 60 gms of proteins and 350 gms of carbohydrates.

Lastly, not all critically ill patients can be fed by enteral nutrition. There are certain contraindications to enteral nutrition. However, in presence of a partially functioning gastrointestinal tract, enteral nutrition should be supplemented by parenteral nutrition and this is termed as partial parenteral nutrition.


Contraindications to Enteral Nutrition:

Inability to meet entire nutrient needs via enteral route
Intestinal obstruction
Paralytic ileus

Doubt regarding adequacy of gastrointestinal function impaired gastrointestinal function due to fluid sequestration in lumen