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 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 total energy expenditures reach 40–45 kcal/kg. The chronically ill patient with lean tissue loss has reduced basal energy expenditure, and inactivity which results in a total energy expenditure of about 20–25 kcal/kg. About 95% of such patients need <30 kcal/kg to achieve energy balance. Because providing about 50% of measured energy expenditure as SNS is at least equally efficacious for the first 10 days of critical illness, actual measurement of energy expenditure is not generally necessary in the early period of SNS. However, in patients who remain critically ill beyond several weeks, in the severely malnourished for whom estimates of energy expenditure are unreliable, or in those who are difficult to wean from ventilators, it is reasonable to actually measure energy expenditure and to aim for energy balance with SNS. Insulin resistance is associated with increased gluconeogenesis and reduced glucose utilization, predisposing a patient to hyperglycemia. This is aggravated in patients receiving exogenous carbohydrate from SNS. Normalization of blood glucose levels by insulin infusion in critically ill patients receiving SNS reduces morbidity and mortality. In mild or moderately malnourished patients, a reasonable goal is to provide metabolic support to improve protein synthesis and maintain metabolic homeostasis. Hypocaloric nutrition providing only about 1000 kcal/d and 70 g protein for up to 10 days requires less fluid and reduces the likelihood of poor glycemic control. Energy content can be advanced to 20–25 kcal/kg with 1.5 g protein/kg as conditions permit and definitely during the second week of SNS. Patients with multiple trauma, closed head injury, and severe burns often have much higher energy expenditures, but there is little evidence that providing more than 30 kcal/kg has additional benefit, and it risks hyperglycemia. Generally, because glucose is an essential tissue fuel, glucose and amino acids are provided parenterally until the level of resting energy expenditure is reached. At this point, adding fat becomes beneficial, since more parenteral glucose stimulates de novo lipogenesis by the liver—an energy-inefficient process. Polyunsaturated long-chain triglycerides are the chief ingredient in most parenteral fat emulsions and the majority of the fat in enteral feeding formulas. These vegetable oil–based emulsions provide essential fatty acids. Enteral feeding formulas have fat content that ranges from 3% of calories up to as much as 50% of calories, while parenteral fat comes in separate containers as 10, 20, and 30% emulsions that can be infused separately or mixed by the pharmacy under controlled conditions as all-in-one or total nutrient admixture with glucose, amino acids, lipid, electrolytes, vitamins, and minerals. Although parenteral fat is required at only about 3% of energy requirements to meet essential fatty acid requirements, when provided as an all-in-one mixture of carbohydrate, fat, and protein, 2–3% fat in the TPN mixtures, representing about 20–30% of calories as fat, is provided to ensure emulsion stability. If given separately, parenteral fat should not be provided at rates exceeding 0.11 g/kg body weight per h or about 100 g over 12 h—equivalent to 1 L of 10% parenteral fat and 500 mL of 20% parenteral fat. Medium-chain triglycerides, which contain saturated fatty acids with chain lengths of 6, 8, 10, or 12 carbons, are provided in a number of enteral feeding formulas because they are absorbed preferentially. Fish oil contains polyunsaturated fatty acids of the omega 3 family, which have been shown to improve immune function and reduce the inflammatory response. 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 PN formulas. In enteral formulas, glucose is the carbohydrate source in so-called monomeric diets. These diets provide protein as amino acids and fat in minimal amounts (3%) to meet essential fatty acid requirements. Monomeric formulas are designed to optimize absorption in the seriously compromised gut. These formulas, like the immune-enhancing diets, are quite expensive. In polymeric diets, the carbohydrate source is usually an osmotically less active polysaccharide, protein is usually soy or casein protein, and fat is present in amounts from 25 to 50%. Such formulas are usually well tolerated by patients with normal intestinal length, and some are acceptable for oral consumption. . Chapter 073. Enteral and Parenteral Nutrition (Part 6) Energy Requirements Total energy expenditure comprises resting. 0.11 g/kg body weight per h or about 100 g over 12 h—equivalent to 1 L of 10% parenteral fat and 500 mL of 20% parenteral fat. Medium-chain triglycerides, which contain saturated fatty acids. since more parenteral glucose stimulates de novo lipogenesis by the liver—an energy-inefficient process. Polyunsaturated long-chain triglycerides are the chief ingredient in most parenteral fat