Nutritional Supplements
Objectives
When you reach the end of this chapter, you will be able to do the following:
Drug Profiles
Key Terms
Anabolism Metabolism characterized by the conversion of simple substances into the more complex compounds; tissue building. (p. 889)
Casein The principal protein of milk and the basis for curd and cheese. (p. 892)
Catabolism A complex metabolic process in which energy is liberated for use in work, energy storage, or heat production by the destruction of complex substances to form simple compounds. (p. 894)
Dumping syndrome A complex reaction to the rapid entry of concentrated nutrients into the jejunum of the small intestine. The patient may experience nausea, weakness, sweating, palpitations, syncope, sensations of warmth, and diarrhea. Most commonly occurs with eating following partial gastrectomy or with enteral feedings that are administered too rapidly into the stomach or jejunum via a feeding tube. (p. 891)
Enteral nutrition The provision of food or nutrients via the gastrointestinal tract, either naturally by eating or through a feeding tube in patients who are unable to eat. (p. 889)
Essential amino acids Those amino acids that cannot be manufactured by the body. (p. 894)
Essential fatty acid deficiency A condition that develops if fatty acids that the body cannot produce are not present in dietary or nutritional supplements. (p. 894)
Hyperalimentation An older term for parenteral nutrition; its use is now discouraged because it may be misinterpreted to mean overfeeding; now referred to as total parenteral nutrition (TPN). (p. 894)
Malnutrition Any disorder of undernutrition. (p. 889)
Multivitamin infusion (MVI) A concentrated solution that contains several water- and fat-soluble vitamins and is used as part of an intravenous (parenteral) nutrition source. (p. 895)
Nonessential amino acids Those amino acids that the body can produce without extracting them from dietary intake. (p. 894)
Nutrients Substances that provide nourishment and affect the nutritive and metabolic processes of the body. (p. 889)
Nutritional supplements Oral, enteral, or intravenous nutritional preparations used to provide optimal nutrients to meet the body’s nutritional needs. (p. 889)
Nutritional support The provision of nutrients orally, enterally, or parenterally for therapeutic reasons. (p. 889)
Parenteral nutrition The administration of nutrients by a route other than through the alimentary canal, such as intravenously. (p. 889)
Semiessential amino acids Those amino acids that can be produced by the body but not in sufficient amounts in infants and children. (p. 894)
Total parenteral nutrition (TPN) The intravenous administration of the total nutrient requirements of the patient with gastrointestinal dysfunction, accomplished via peripheral or central venous catheter. (p. 892)
Whey The thin serum of milk remaining after the casein and fat have been removed. It contains proteins, lactose, water-soluble vitamins, and minerals. (p. 892)
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Anatomy, Physiology, and Pathophysiology Overview
Nutrients are dietary products that undergo chemical changes when ingested (and metabolized) that cause tissue to be enhanced and energy to be liberated. Nutrients are required for cell growth and division; enzyme activity; protein, carbohydrate, and fat synthesis; muscle contraction; secretion of hormones (e.g., vasopressin, gastrin); wound repair; immune competence; gut integrity; and numerous other essential cellular functions. Providing for these nutritional needs is known as nutritional support. Adequate nutritional support is needed to prevent the breakdown of tissue proteins for use as an energy supply to sustain essential organ systems, which is what occurs during starvation. Malnutrition can decrease organ size and impair the function of organ systems (e.g., cardiac, respiratory, gastrointestinal, hepatic, renal). Nutritional supplements are a means of providing adequate nutritional support to meet the body’s nutritional needs.
Malnutrition is a condition in which the body’s essential need for nutrients is not met by nutrient intake. The purpose of nutritional support is the successful prevention, recognition, and management of malnutrition. Nutritional supplements are dietary products used to provide nutritional support. Nutritional supplement products can be administered to patients in a variety of ways. They vary in the amount and chemical complexity of the carbohydrates, proteins, fats, electrolytes, vitamins, and minerals that compose them, as well as in their osmolality. These nutrients may be given in a digested form, a partially digested form, or an undigested form. Nutritional supplements can also be tailored for specific disease states.
Patients’ nutrient requirements vary according to age, gender, size or weight, physical activity, preexisting medical conditions, nutritional status, and current medical or surgical treatment. Nutritional supplements are classified according to the method of administration as either enteral or parenteral. Enteral nutrition is the provision of food or nutrients via the gastrointestinal tract. Nutritional supplements may also be administered parenterally. Parenteral nutrition is the intravenous administration of nutrients. Its purpose is to promote anabolism (tissue building), nitrogen balance, and maintenance or improvement of body weight. It is used when the oral or enteral feeding routes cannot be used (e.g., in postoperative patients or patients who are cachectic from advanced cancer or acquired immunodeficiency syndrome [AIDS]). The selection of either enteral nutrition or parenteral nutrition and the specific nutritional composition of the product used depend on the specific patient and the clinical situation. Enteral nutrition is used when the patient has a functioning gastrointestinal tract.
Pharmacology Overview
Enteral Nutrition
Enteral nutrition is the provision of food or nutrients through the gastrointestinal tract. The most common and least invasive route of administration is oral consumption. A feeding tube is used in the other five enteral routes (Figure 55-1). The six routes of enteral nutrition delivery are listed in Table 55-1.
TABLE 55-1
ROUTES OF ENTERAL NUTRITION DELIVERY
ROUTE | DESCRIPTION |
Esophagostomy | Feeding tube surgically inserted into the esophagus |
Gastrostomy | Feeding tube surgically inserted directly into the stomach |
Jejunostomy | Feeding tube surgically inserted into the jejunum |
Nasoduodenal | Feeding tube placed from the nose to the duodenum |
Nasojejunal | Feeding tube placed from the nose to the jejunum |
Nasogastric | Feeding tube placed from the nose to the stomach |
Oral | Nutritional supplements delivered by mouth |
Patients who may benefit from feeding tube delivery of nutritional supplements include those with abnormal esophageal or stomach peristalsis, altered anatomy secondary to surgery, depressed consciousness, or impaired digestive capacity. The enteral route is considered to be the superior route of administration of nutritional supplements.
Approximately 100 different enteral supplement formulations are available. The enteral supplements have been divided into groups according to the basic characteristics of the individual formulations. The enteral formulation groups are elemental, polymeric, modular, altered amino acid, and impaired glucose tolerance. These are described in Box 55-1.
Mechanism of Action and Drug Effects
The enteral formula groups provide the basic building blocks for anabolism. Different combinations and amounts of these nutrients are used based on the individual patient’s anabolic needs. Enteral nutrition supplies complete dietary needs through the gastrointestinal tract by the normal oral route or by feeding tube.
Indications
Enteral nutrition can be used to supplement an oral diet that is currently insufficient for a patient’s nutrient needs or used alone to meet all of the patient’s nutrient needs. Box 55-2 lists the main types of enteral nutritional supplements and their indications.
Contraindications
The usual contraindication to nutritional supplements of any kind is known allergy to a specific product or genetic disease that renders a patient unable to metabolize certain types of nutrients.
Adverse Effects
The most common adverse effect of nutritional supplements is gastrointestinal intolerance, manifesting as diarrhea. Infant nutritional formulations are most commonly associated with allergies and digestive intolerance. The other nutritional supplements are commonly associated with osmotic diarrhea. Rapid feeding or bolus doses can result in dumping syndrome, which produces intestinal disturbances. In addition, tube feeding places the patient at significant risk for aspiration pneumonia. This is especially true in patients in whom mental status, gag reflexes, and general mobility are compromised.
Interactions
Various nutrients can interact with drugs to produce significant food-drug interactions. With some exceptions, food usually delays the absorption of drugs when administered simultaneously. High gastric acid content or prolonged emptying time can result in decreased effects of certain antibiotics (cephalosporins, erythromycin, and penicillins). An increased absorption rate resulting in increased therapeutic effects can be seen when corticosteroids or vitamins A and D are given with nutritional supplements. The antibiotic effects of tetracyclines and quinolones are decreased when they are given with nutritional supplements as a result of chemical inactivation. These drugs must be given at least 2 hours before or after tube feedings.
Tube feedings can also reduce the absorption of phenytoin, which may result in seizures. It is recommended that tube feedings be held for at least 2 hours before and after the administration of phenytoin. This can be problematic, because the patient may not receive adequate nutrition due to withholding of feedings. This issue is somewhat controversial, and some suggest that the interaction is more theoretical than actual. Thus, some institutions have decided to ignore this possible interaction and to monitor phenytoin levels and patient status, rather than holding the tube feedings, whereas others continue to hold the tube feedings. Often the patient requires intravenous phenytoin when continuous tube feedings are necessary.
Dosages
Because nutrient requirements vary greatly, dosages are individualized according to patient needs.
Drug Profiles
Enteral nutrition can be provided by a variety of supplements. Individual patient characteristics determine the appropriate enteral supplement. The four most commonly used enteral formulations are elemental, polymeric, modular, and altered amino acid.
Elemental Formulations
Elemental formulations are enteral supplements that contain dipeptides, tripeptides, or crystalline amino acids. Minimal digestion is required with elemental formulations. These supplements are indicated for patients with pancreatitis, partial bowel obstruction, irritable bowel disease, radiation enteritis, bowel fistulas, and short bowel syndrome. They are contraindicated in patients who have had hypersensitivity reactions to them. Elemental formulation supplements are available without a prescription and have no pregnancy category.
Polymeric Formulations
Polymeric formulations are enteral supplements that contain complex nutrients derived from proteins, carbohydrates, and fat. The polymeric formulations are some of the most commonly used enteral formulations because they most closely resemble normal dietary intake. They are preferred over elemental formulations in patients who have fully functional gastrointestinal tracts and have no specialized nutrient needs. Polymeric formulations are less hyperosmolar than elemental formulations and therefore cause fewer gastrointestinal problems. They are contraindicated in patients who have had hypersensitivity reactions to them. They are available without a prescription and have no pregnancy category classification.
The most commonly used enteral supplement in the polymeric formulation category of enteral nutrition products is Ensure. It is lactose free and is also available in a higher-calorie formula called Ensure Plus. Other polymeric formulations are listed in Box 55-1. These drugs contain complex nutrients such as casein and soy protein for protein, corn syrup, and maltodextrins for carbohydrates, and vegetable oil or milk fat for fat. They are available in liquid formulations only.
Modular Formulations
carbohydrate formulation
Moducal and Polycose are examples of commonly used enteral supplements in the carbohydrate modular formulation category. Both are carbohydrate supplements that supply carbohydrates only. They are intended to be used in addition to monomeric or polymeric formulations to provide a more individual specialized nutrient mix. They are available in liquid formulations only. These products are obtainable without a prescription, have no pregnancy category classification, and are contraindicated only in patients who have had hypersensitivity reactions to them.
fat formulation
Microlipid and MCT Oil are the formulations available in the fat category. Microlipid is a fat supplement supplying only fats. It is a concentrated source of calories and contains 4.5 kcal/mL. These drugs are given to help individualize nutrient formulations. They may be used in patients with malabsorption and other gastrointestinal disorders and in patients with pancreatitis. They are available in liquid formulations only. These products are obtainable without a prescription, have no pregnancy category classification, and are contraindicated only in patients who have had hypersensitivity reactions to them.
protein formulation
Casec, ProMod, and Propac are examples of protein modular formulations. They are used to increase patients’ protein intake and provide additional proteins. They are derived from a variety of sources such as whey, casein, egg whites, and amino acids. All of the available products are dried powders that must be reconstituted with water. They may sometimes be reconstituted by placing them in enteral feedings that are already in liquid form. They are indicated for patients with increased protein needs. They are contraindicated in patients who have had hypersensitivity reactions to them. Protein formulation supplements are available without a prescription and have no pregnancy category classification.
Altered Amino Acid Formulations
Amin-Aid is one of the many amino acid formulation nutritional supplements available. Many of the nutritional supplements in this category are also listed as modular formulations because they can be used as both single-nutrient formulas and as nutritional formulations for patients with genetic errors of metabolism. Specialized amino acid formulations are used most commonly in patients who have metabolic disorders such as phenylketonuria, homocystinuria, and maple syrup urine disease. They are also used to supply nutritional support to patients with illnesses such as renal impairment, eclampsia, heart failure, or liver failure.
Parenteral Nutrition
Parenteral nutritional supplementation (intravenous administration) is the preferred method for patients who are unable to tolerate and/or maintain adequate enteral or oral intake. Instead of administration of partially digested nutrients into the gastrointestinal tract (as in enteral nutrition), vitamins, minerals, amino acids, dextrose, and lipids are administered intravenously directly into the circulatory system. This effectively bypasses the entire gastrointestinal system, which eliminates the need for absorption, metabolism, and excretion. Parenteral nutrition is also called total parenteral nutrition (TPN) or hyperalimentation.
TPN can supply all of the calories, carbohydrates, amino acids, fats, trace elements, vitamins, and minerals needed for growth, weight gain, wound healing, convalescence, immunocompetence, and other health-sustaining functions.
TPN can be administered through either a peripheral vein or a central vein. Each route of delivery of TPN has specific requirements and limitations. It is generally accepted that TPN is used only when oral or enteral support is impossible or when the gastrointestinal absorptive or functional capacity is not sufficient to meet the nutritional needs of the patient. Some of the factors that must be considered in deciding whether to use peripheral or central TPN for a given patient are listed in Table 55-2.
TABLE 55-2
PERIPHERAL AND CENTRAL PARENTERAL NUTRITION: CHARACTERISTICS
CHARACTERISTIC | PERIPHERAL | CENTRAL |
Goal of nutritional therapy (total versus supplemental) | Supplemental (total if moderate to low needs) | Total |
Length of therapy | Short (fewer than 14 days) | Long (7 days or longer) |
Osmolarity | Hyperosmolar (600-900 mOsm/L) | Hyperosmolar (600-900 mOsm/L) |
Fluid tolerance | Must be high | Can be fluid restricted |
Dextrose | Less than 10%∗ | 10%-35% |
Amino acids | Less than 3% | More than 3%-7% |
Fats | 10%-20% | 10%-20% |
Calories per day | Less than 2000 kcal/day | More than 2000 kcal/day |