? Explain the alterations in energy metabolism in stress and starvation.
? Assess energy requirements of patients during stress and starvation.
? Summarize feeding routes, indications, and risks for patients who cannot eat.
? Describe the consequences of bypassing the gut during feeding.
? Outline the pathophysiology and treatment of refeeding syndrome, and identify
patients at risk.
GI Tract and Metabolism
Normal and Altered Intestine
GI Hormone Response
Glutamine Metabolism in Stress
Sources of Glutamine
Short-Chain Fatty Acids
Importance of Enteral and Parenteral Nutrition
Enteral and Parenteral Feeding
Nutrient Transport with Oral or Enteral Feeding
Nutrient Transport with Parenteral Feeding
Components of Energy Expenditure
Basal Energy Expenditure and Thermic Effect of Food
Growth and Lactation
Body Composition in Non-Obese Individuals
Indirect Calorimetry: Sample Calculation
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Hypermetabolism and Fever Refeeding Syndrome
Pathophysiology of Refeeding Syndrome
Patients at Risk for Refeeding
Preventing Refeeding Syndrome TPN
Complications of Long-Term TPN Enteral Feeding
The Nutrition Plan
Under- or Overfeeding
Integrated Practice (Nutrition Support)
Nutrition Support Handouts 2
Objectives, Key Concepts, and Key Concept Summaries by Topic
Topic: Gut Nutrition
Explain the effect of feeding via the GI tract on metabolism.
Bypassing the gut by feeding intravenously alters the structure and function of the gastrointestinal tract.
Food in the stomach stimulates gastrin secretion and gastric acid production. The presence of food and a low pH in the duodenum causes cholecystokinin (CCK) secretion and secretin stimulation. Parenteral feeding bypasses the GI tract and therefore does not stimulate secretion of intestinal hormones. Absence of CCK secretion can stop bile flow (cholestasis). With parenteral feeding, changes in the intestinal mucosa can occur. Over time, intestinal atrophy may allow bacteria and toxins to enter the bloodstream and may impair nutrient absorption. Glutamine, a conditionally essential amino acid, is an important oxidative fuel for the intestinal mucosa. During stress the demand for glutamine may exceed the supply. Inadequate supplies of glutamine can result in deterioration of the mucosal barrier.
Topic: Feeding Route
Describe feeding routes for patients who cannot eat.
Patients who cannot eat should receive enteral or parenteral nutrition.
Nutrition can be provided through alternate routes, such as enterally (into the stomach or small intestine) or parenterally (into a central or peripheral vein). When the GI tract is not functional, patients should be fed parenterally. In such cases, enteral feeding should begin as soon as ability to digest and absorb nutrients resumes, even if the majority of nutrition is provided parenterally. Patients with normal lower GI function, but who cannot swallow or maintain adequate oral intake should be fed enterally. Appropriate nutrition decreases length of hospital stay, reduces the risk of post-op complications, and improves wound healing. There are metabolic consequences to intravenous feedings because it bypasses the normal absorption and transport processes-- intravenous lipids enter the circulation as droplets without the apoproteins found on chlyomicrons.
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Topic: Energy Expenditure
Describe the components of and factors that influence total energy expenditure.
Basal metabolism, physical activity, and thermic effect of food comprise total energy expenditure in healthy individuals.
Total energy expenditure has three components: basal metabolic rate (BMR), physical activity, and diet-induced thermogenesis (thermic effect of food). BMR represents the energy used by the body in a restful, awake state. This is the energy needed for ion pumping, protein synthesis, and all homeostatic functions. BMR depends mainly on body size and composition. Understanding body composition is important to clinical assessment of nutritional status. In both stress and malnutrition, body composition is altered because of loss of protein mass. Energy expenditure increases in stressed patients; the amount of increase depends upon the degree of illness. Changes in nutritional recommendations are concurrent with changes in body composition. Physical activity is the most variable component of total energy expenditure in healthy individuals.
Specify how indirect calorimetry can be used to estimate energy expenditure.
Indirect calorimetry can be used to estimate energy expenditure by using the respiratory quotient.
Indirect calorimetry is a method of estimating energy expenditure based on CO2 production and O2 uptake. It is often used in a clinical setting to get a reliable estimate of energy expenditure and prevent over- or under-feeding of critically ill, malnourished, or extremely obese patients. A metabolic cart can take the measurements, determine the respiratory quotient (RQ; ratio of CO2 to O2), and convert the RQ into estimated expenditure. The equations for the oxidation of carbohydrates and fats show that known amounts of O2 and CO2 correspond to predictable amounts of energy production. Because glucose and fat are completely oxidized, energy production from glucose or fat oxidation can be predicted by measuring consumption of oxygen and production of carbon dioxide. Protein oxidized can be calculated from urinary nitrogen excretion.
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Topic: Energy Assessment
Describe how energy needs may be estimated in clinical settings.
Standardized prediction equations exist for estimating energy expenditure but have limited usefulness in critically ill patients.
Indirect calorimetry is a reliable method for determining an individual’s energy expenditure, but it is not always feasible in clinical practice. Many standardized formulas exist to estimate energy expenditure based on a patient’s age, height, weight, and physical
activity level. Many of these, however, were developed for healthy people and thus are not appropriate for critically ill patients. Furthermore, during stress, hypermetabolism and fever cause energy needs to increase. Stressed patients have high energy expenditures and increased protein turnover due to the hypermetabolism characteristic of the stress response. Hypermetabolism increases with severity of the trauma. With many diseases and traumas, fever is also present. Each degree rise in temperature above 37 degrees C elevates metabolic rate by about 10%.
Topic: Refeeding Syndrome
Outline the pathophysiology and treatment of refeeding syndrome, and identify patients at risk.
Refeeding syndrome is characterized by metabolic events that occur upon feeding severely malnourished patients.
Refeeding syndrome can occur with any type of feeding following a period of nutritional deprivation. Glucose moves into cells, and along with it, phosphorous, potassium, and magnesium, causing the serum concentrations of these minerals to drop abruptly. The severe mineral and fluid imbalances that occur with refeeding can lead to cardiac arrest, neuromuscular complications, or respiratory dysfunction. Malnourished patients with poor nutritional stores due to limited intake (i.e. anorexia nervosa, elderly patients with depression or dementia, cancer cachexia, malnutrition due to hunger, stress, or fasting) are at-risk. Refeeding syndrome can be prevented by avoiding sudden overfeeding, avoiding excess glucose, replacing phosphorus, magnesium, and potassium, restricting fluid intake, initiating sodium administration slowly, and providing thiamin.
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List three complications that can occur from long-term parenteral feeding.
Complications can occur from long-term parenteral feeding.
When nutrition is provided directly into the bloodstream, determining the patient’s
nutritional needs as accurately as possible becomes critically important. Short-bowel
syndrome is one condition that may require long-term parenteral feeding. Parenteral
feeding is not without risk. Catheter-related infection, metabolic bone disease, liver
disease, and micronutrient deficiencies are serious risks of long-term parenteral feeding.
Topic: Enteral Feeding
Describe complications that can occur with enteral feeding.
Enteral feeding is not without risks..
When nutrition is provided directly into the GI tract, determining the patient’s nutritional
needs as accurately as possible becomes critically important. Enteral feeding can lead to
reflux of stomach contents into the lungs, which can lead to aspiration pneumonia.
Diarrhea can be a common problem in enterally fed patients. Other serious problems may
include refeeding syndrome, or altered glucose, lipid, or acid-base balance.
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Topic: Nutrition Plan
Characterize the factors considered in formulating a nutrition plan.
Formulating a nutrition plan is essential in the care of critically ill patients.
Nutrition assessment provides a picture of the patient’s nutritional risk. This requires
collecting and evaluating information obtained from the patient’s history, physical exam,
anthropometric measurements, and labs. From the information obtained in the nutritional
assessment, a plan for the patient is formulated. The plan must be individualized to meet
the patient’s requirements for protein, energy, and other nutrients. It should also include
the goals for nutritional intake, and the most appropriate route of feeding and formula
composition to achieve those goals. In the stressed patient, the goal is usually to prevent
further depletion of lean body mass. Underfeeding can result in poor wound healing,
weakness, and malnutrition as protein is used as an energy source. Overfeeding can result
in hyperglycemia, carbon dioxide retention, and fatty liver.
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American Dietetic Association’s Nutrition Care Manual,
http://www.nutritioncaremanual.org, accessed 10 October, 2006.
ASPEN Board of Directors and the Clinical Guidelines Task Force. Guidelines for the use of parenteral and enteral nutrition in adult and pediatric patients.JPEN J Parenter Enteral Nutr. 2002 Jan-Feb;26(1 Suppl):1SA-138SA.
Berger MM, Spertinini F, Shenkin A, Wardle C, Wiesner L, Schindler C, Chiolero RL. Trace element supplementation modulates pulmonary infection rates after major burns: a double-blind, placebo-controlled trial. Am J Clin Nutr 1998;68:365-371
Biffl WL, Moore EE, Haenel JB. Nutrition support of the trauma patient. Nutrition 2002;18:960-965
Boitano, M. Hypocaloric feeding of the critically ill. Nutr Clin Pract. 2006 Dec;21(6):617-22.
Brehm BJ, Spang SE, Lattin BL, Seeley RJ, Daniels SR, D’Alessio DA. The role of energy expenditure in the differential weight loss in obese women on low-fat and low-carbohydrate diets. J Clin Endocrinol Metab. 2005 Mar;90(3):175-82. Epub 2004 Dec 14.
Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride.Institute of Medicine, National Academy Press, Washington, DC. 1997. Available at.www.nap.edu
Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients).Institute of Medicine, National Academy Press, Washington, DC. 2005. Available at.www.nap.edu
Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Institute of Medicine, National Academy Press, Washington, DC. 2005. Available
Ehrlich HP, Tarver H, Hunt TK. Effects of vitamin A and glucocorticoids upon inflammation and collagen synthesis. Ann Surg 1973;177:222-227
Hoffer LJ. Protein and energy provision in critical illness. Am J Clin Nutr 2003;78:906-11.
Levine JA. Nonexercise activity themogenesis(NEAT): environment and biology. AM J Physiol Endocrinol Metab 2004;286:E675-E685.
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Kattlemann et al, Preliminary evidence for a medical nutrition therapy protocol: enteral feedings for critically ill patients. J Am Diet Assoc. 2006 Aug;106(8):1226-41. Review.
McClain CJ, Twyman DL, Ott LG, Rapp RP, Tibbs PA, Norton JA, Karsakis EJ, Dempsey RJ, Young B. Zinc supplementation is associated with improved neurologic recovery rate and visceral protein levels of patients with severe closed head injury. J Neurotrauma 1996;13:25-34
McCray S, Walker S, Parrish CR. Much Ado About Refeeding. Practical
Gastroenterology January 2005; series #23:26-44.
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