Chapter 073. Enteral and Parenteral Nutrition (Part 6)

Energy RequirementsTotal energy expenditure comprises resting energy expenditure (two-thirds) plus activity energy expenditure (one-third) (Chap. 72). Resting energy expenditure includes the calories necessary for basal metabolism at bed rest. Activity energy expenditure represents one-fourth to one-third of the total, and the thermal effect of feeding is about 10% of the total energy expenditure. For normally nourished healthy individuals, the total energy expenditure is about 30– 35 kcal/kg. Although critical illness increases resting energy expenditure, only in initially well-nourished individuals with the highest systemic inflammatory response, such as that from severe multiple trauma, burns, closed head injury, or sepsis, do...
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Chapter 073. Enteral and Parenteral Nutrition (Part 6) Chapter 073. Enteral and Parenteral Nutrition (Part 6) Energy Requirements Total energy expenditure comprises resting energy expenditure (two-thirds)plus activity energy expenditure (one-third) (Chap. 72). Resting energyexpenditure includes the calories necessary for basal metabolism at bed rest.Activity energy expenditure represents one-fourth to one-third of the total, and thethermal effect of feeding is about 10% of the total energy expenditure. Fornormally nourished healthy individuals, the total energy expenditure is about 30–35 kcal/kg. Although critical illness increases resting energy expenditure, only ininitially well-nourished individuals with the highest systemic inflammatoryresponse, such as that from severe multiple trauma, burns, closed head injury, orsepsis, do total energy expenditures reach 40–45 kcal/kg. The chronically illpatient with lean tissue loss has reduced basal energy expenditure, and inactivitywhich results in a total energy expenditure of about 20–25 kcal/kg. About 95% ofsuch patients need often have much higher energy expenditures, but there is little evidence thatproviding more than 30 kcal/kg has additional benefit, and it risks hyperglycemia. Generally, because glucose is an essential tissue fuel, glucose and aminoacids are provided parenterally until the level of resting energy expenditure isreached. At this point, adding fat becomes beneficial, since more parenteralglucose stimulates de novo lipogenesis by the liver—an energy-inefficient process. Polyunsaturated long-chain triglycerides are the chief ingredient in mostparenteral fat emulsions and the majority of the fat in enteral feeding formulas.These vegetable oil–based emulsions provide essential fatty acids. Enteral feedingformulas have fat content that ranges from 3% of calories up to as much as 50% ofcalories, while parenteral fat comes in separate containers as 10, 20, and 30%emulsions that can be infused separately or mixed by the pharmacy undercontrolled conditions as all-in-one or total nutrient admixture with glucose, aminoacids, lipid, electrolytes, vitamins, and minerals. Although parenteral fat is required at only about 3% of energy requirementsto meet essential fatty acid requirements, when provided as an all-in-one mixtureof carbohydrate, fat, and protein, 2–3% fat in the TPN mixtures, representingabout 20–30% of calories as fat, is provided to ensure emulsion stability. If givenseparately, parenteral fat should not be provided at rates exceeding 0.11 g/kg bodyweight per h or about 100 g over 12 h—equivalent to 1 L of 10% parenteral fatand 500 mL of 20% parenteral fat. Medium-chain triglycerides, which contain saturated fatty acids with chainlengths of 6, 8, 10, or 12 carbons, are provided in a number of enteral feedingformulas because they are absorbed preferentially. Fish oil contains polyunsaturated fatty acids of the omega 3 family, whichhave been shown to improve immune function and reduce the inflammatoryresponse. Parenteral emulsions containing medium-chain triglycerides, olive oil,and fish oil are available in Europe and Japan but not yet in the United States. Carbohydrates are provided as hydrous glucose providing 3.4 kcal/g in PNformulas. In enteral formulas, glucose is the carbohydrate source in so-calledmonomeric diets. These diets provide protein as amino acids and fat in minimalamounts (3%) to meet essential fatty acid requirements. Monomeric formulas are designed to optimize absorption in the seriouslycompromised gut. These formulas, like the immune-enhancing diets, are quiteexpensive. In polymeric diets, the carbohydrate source is usually an osmoticallyless active polysaccharide, protein is usually soy or casein protein, and fat ispresent in amounts from 25 to 50%. Such formulas are usually well tolerated bypatients with normal intestinal length, and some are acceptable for oralconsumption.