Gastroenterology and Hepatology Board Review: Pearls of Wisdom, Third Edition


CHAPTER 43. Clinical Nutrition, Enteral, and Parenteral Nutrition Support

Carol Rees Parrish, MS, RD and Joe Krenitsky, MS, RD

Image Some individuals with achlorhydria may need supplementation of which vitamin? Why?

Vitamin B12. Both acid and intrinsic factor are produced in the gastric parietal cell. In some conditions (eg, pernicious anemia), the parietal cell has diminished, or absent, production of both acid and intrinsic factor leading to achlorhydria and vitamin B12 deficiency.

Image Macrocytic anemia may result from deficiencies of which two B vitamins?

Folate and vitamin B12.

Image What biliary factors may contribute to fat malabsorption?

Any condition that decreases bile flow or excretion, or disrupts the enterohepatic circulation of bile salts in the ileum.

Image True/False: An individual with a more than 100-cm terminal ileal resection is at risk of developing vitamin D deficiency.

True. Disrupted enterohepatic cycling of bile acids in those with more than 100 cm of distal ileum removed may result in bile salt deficiency that can lead to fat malabsorption, including fat-soluble vitamins (A, D, E, and K).

Image What individuals are at risk of developing refeeding syndrome?

Anyone with an unintentional, chronic (> 10 days) inadequate intake.

Image What classical electrolyte disturbances occur with refeeding syndrome?

Hypokalemia, hypophosphatemia, and hypomagnesemia.

Image In patients at nutritional risk, especially alcohol abusers, which vitamin should be given prior to the administration of intravenous glucose? Why?

Thiamine (vitamin B1). Thiamine is a cofactor for several enzymes essential for optimal glucose utilization and metabolism. Thiamine requirements depend on metabolic rate, with the greatest need during periods of high metabolic demand and high glucose intake. This is manifest by the precipitation of Wernicke’s encephalopathy in susceptible patients by administration of intravenous glucose before thiamine supplementation.

Image What conditions are associated with thiamine deficiency and what conditions are they at risk of developing?

Alcoholism, anorexia nervosa, hyperemesis of pregnancy, prolonged fasting or starvation, gastrointestinal surgery (eg, gastric bypass), long-term parenteral nutrition, AIDS, transplantation, and hemodialysis. Thiamine deficiency may be complicated by the development of Wernicke’s encephalopathy (triad of encephalopathy, oculomotor dysfunction, and gait ataxia) and Korsakoff’s psychosis.

Image What endogenous substance initiates the cascade of events that causes refeeding syndrome?


Image True/False: Wet beriberi and dry beriberi are both the result of niacin deficiency.

False. Beriberi results from thiamine deficiency. Wet beriberi refers to the type with prominent cardiac manifestations, whereas dry beriberi refers to the type with prominent neurological manifestations.

Image How much fat is required in the diet to prevent essential fatty acid (EFA) deficiency?

3%–4% of the total calories.

Image How much fat is required in the diet to have adequate absorption of fat-soluble vitamins?


Image Neutropenia may be caused by which trace element deficiency?

Copper. Copper deficiency is an underrecognized cause of anemia, neutropenia, and bone marrow dysplasia. Neuromuscular disturbances may also occur. Zinc toxicity and prior gastric surgery (resection in particular) have been described as the causes of copper deficiency. Cytopenias typically resolve with the correction of the copper deficiency.

Image True/False: Vitamin E is produced in the gut on a daily basis.

False. Vitamin K is produced by intestinal microbes.

Image What is an acceptable gastric residual volume (GRV) for a patient receiving gastric tube feeding?

Up to 500 mL. However, if GRV is used, it should be in addition to abdominal assessment for distention, nausea, and vomiting. Despite its common use, very little data exist to support the practice of checking GRV.

Image Why is it inappropriate to bolus tube feed into the small intestine?

The small intestine is very sensitive to volume/distension.

Image Medium chain triglyceride (MCT) oil is sometimes offered to patients with severe fat malabsorption as a calorie supplement. What are the potential gastrointestinal side effects of excess MCT oil in the diet?

Excess gas, bloating, diarrhea, and anal seepage.

Image True/False: The main advantage of MCTs over long chain triglycerides (LCTs) is their ability to be absorbed directly across the small bowel mucosa.

True. MCT does not require micelle formation for absorption.

Image True/False: MCT does not contain EFAs, so those receiving supplemental MCT will still require a source of EFA.

True. Another disadvantage of MCTs over LCTs is that they provide fewer calories (8 versus 9 kcal/g).

Image True/False: Residual volumes should be checked in a patient receiving nasoduodenal feedings.

False. The small bowel has no reservoir and therefore checking for residuals is unnecessary.

Image True/False: Accumulating evidence supports a preference of parenteral over enteral nutrition support in the critically ill patient with severe acute pancreatitis.

False. Compared to parenteral nutrition support, enteral nutrition support has been shown to result in better outcomes (including a Cochrane Review), particularly when the feeding is administered distal to the ligament of Treitz.

Image What nutritional laboratory parameters need to be monitored closely in a patient with pancreatitis who is receiving parenteral nutrition with lipids?

Serum triglycerides and blood glucose levels. Elevated serum triglyceride level is often a function of hyperglycemia as lipoprotein lipase activity decreases along with clearance of triglycerides from the bloodstream beginning as glucose rises over 150 mg/dL.

Image True/False: A 63-year-old man has been tolerating tube feeding for 3 weeks and suddenly develops a stool output of 950 mL/day. The enteral formula is the most likely cause of the sudden increase in stool output.

False. In this situation, especially if tolerance had been good, an investigation for other causes of diarrhea should be initiated. Potential causes include gut infections, particularly Clostridium difficile, and the use of medications given through the feeding tube that contain sorbitol or other sugar alcohols.

Image With regard to the previous question, what changes could you make to the tube feeding regimen without compromising his/her nutritional status?

Nothing. The problem is rarely related to the tube feeding itself.

Image True/False: Whenever possible, all medications administered through a feeding tube should be given as solutions or elixirs.

True. Crushed medications have the potential to clog the feeding tube. However, elixirs can precipitate diarrhea due to sugar alcohol content.

Image In a patient with severe acute pancreatitis requiring enteral nutritional support, name the jejunal access options.

Nasojejunal, combined nasogastric-jejunal tube (for gastric venting and jejunal feeding), percutaneous endoscopic/radiologic gastrostomy-jejunostomy, direct percutaneous endoscopic/radiologic jejunostomy, and surgical jejunostomy.

Image Skin site infections occur in approximately what percentage of patients following percutaneous endoscopic gastrostomy (PEG) placement?


Image True/False: An overly tight external bolster is the biggest risk factor associated with buried bumper syndrome.


Image A 54-year-old woman is hospitalized 1 year status post Roux-en-Y gastric bypass surgery with severe ataxia, peripheral neuropathy, and myeloneuropathy. What micronutrient deficiency is the most likely cause of these symptoms?


Image True/False: The initial nutritional management for a chyle leak consists of a very low fat diet or enteral formula prior to using parenteral nutrition.

True. Chyle, containing ingested fat and protein, electrolytes, lymphocytes, and other substances, is absorbed from the GI tract into the lymph system where it travels and ultimately is returned to the circulation via the subclavian vein over a period of several hours.

Image True/False: If a patient with a chyle leak requires parenteral nutrition support, intravenous lipids must be withheld.

False. Intravenous lipid emulsions are infused directly into the blood stream and do not enter the lymph system.

Image True/False: EFA deficiency can be determined by checking a triene:tetraene ratio.

True. A triene: tetraene ratio > 0.4 is generally considered to indicate an EFA deficiency.

Image True/False: The EFAs are linoleic acid (omega-6) and linolenic acid (omega-3).

True. Linoleic is the primary EFA. Corn, flaxseed, soybean, and sunflower oils are all high in EFA.

Image True/False: Serum proteins such as albumin or prealbumin are accurate indicators of nutritional status in hospitalized patients.

False. Serum proteins are inverse acute phase reactants and do not correlate with nutrition intake, and should not be used as a marker of nutritional status.

Image What conditions, other than malnutrition, may result in decreased serum albumin and prealbumin?

Renal disease, liver disease, hydration, chemotherapy, blood loss, or any physiologic stress such as a surgical procedure or infection that results in an acute phase response.

Image What clinical factors are most likely to indicate compromised nutrition status?

Unplanned weight loss and decreased oral intake (below 50%–75% of normal) for 1 week or greater.

Image True/False: Obese patients are rarely malnourished.

False. Obese patients may have poor oral intake for a prolonged period with significant weight loss that is not initially apparent because they remain obese. Considering the increasing incidence of obesity in the United States, it is likely that the incidence of malnourished obese patients seen in practice will increase.

Image True/False: All patients receiving mechanical ventilation require a specialized pulmonary enteral formula.

False. Use of specialized pulmonary formulas has not been demonstrated to decrease time requiring mechanical ventilation or improve other outcomes in randomized, controlled studies.

Image What are the macronutrient characteristics that make a pulmonary enteral formula unique and theoretically beneficial to the mechanically ventilated patient?

High fat and low carbohydrate. This theoretically results in reduced carbon dioxide levels and a reduced work of breathing, thereby facilitating weaning from the ventilator. These benefits have not been borne out in clinical practice.

Image List factors that may contribute to aspiration in a gastrostomy tube-fed patient.

Head of bed elevation less than 30 degrees during formula infusion, delayed gastric motility, depressed cough reflex, and a rapid infusion of large bolus feeding.

Image What are clinical implications of providing excess parenteral dextrose?

Exacerbation of hyperglycemia, which may cause hypertriglyceridemia and increase the risk of infection, and hepatic steatosis with elevated liver tests.

Image How many days after the initiation of parenteral nutrition support will a rise in liver tests typically occur?

Ten to twelve days.

Image True/False: Critically ill patients who do not tolerate full enteral nutrition support within 2–3 days should be started on parenteral nutrition to prevent malnutrition.

False. An early start of parenteral nutrition support has recently been shown to result in increased complications without apparent benefit.

Image List the mechanisms through which hyperglycemia can impair or negate efforts to improve nutrition status.

Increased catabolism and muscle breakdown, decreased gastric motility with impaired food intake or impaired enteral feeding tolerance, and calories lost through glucosuria.

Image True/False: Only long-term hyperglycemia affects gastric motility.

False. Acute hyperglycemia decreases motility in the stomach, duodenum, and jejunum.

Image How long does it take to develop biochemical evidence of an EFA deficiency on a fat-free diet?

Three weeks.

Image What two organs are storage sites for vitamin A?

Adipose tissue and liver.

Image Name one complication that can result from megadoses of vitamin D.

Soft tissue calcium deposition.

Image True/False: Patients with end-stage kidney disease receiving maintenance hemodialysis or peritoneal dialysis should receive a reduced-protein feeding formula.

False. Patients receiving maintenance hemodialysis have increased losses of amino acids, peptides, and proteins during the dialysis process and thus have increased protein needs of 1.3–1.4 g protein/kg compared to the healthy adult protein requirements of 0.8–1.0 g protein/kg.

Image What specific nutritional characteristics of a renal enteral formula make it clinically useful in a patient with end-stage renal disease?

Lower amounts of potassium, magnesium, and phosphorus, and increased caloric density to provide more calories in less volume. All patients on dialysis should receive increased protein.

Image Why is the total amount of calcium and phosphorus limited in a parenteral nutrition solution?

An excess in the total calcium/phosphate product will cause precipitate formation in the solution.

Image List the advantages of continuous enteral feeding into the jejunum compared to the stomach.

Potentially lower risk of aspiration, particularly for those patients with poor gastric motility.

Image What are feeding restrictions of jejunal feedings?

Very rapid infusions (> 150 mL/h) or very hyperosmolar (> 750 mOsm/L) formulas may not be well tolerated initially. Most standard polymeric, nutrient-dense, or fiber-containing feedings are well tolerated in patients with a normal GI anatomy and function when the formulas are started at reduced rates and then increased. High fiber, nutrient-dense formulas can clog very small caliber tubes (< 8 French) used for jejunal feeds.

Image What are potential complications of a surgical jejunostomy?

Infection, bowel obstruction, bowel torsion, dislodgement, leakage, bowel necrosis, and the general risks of surgery and anesthesia.

Image A 45-year-old woman on long-term home parenteral nutrition for short bowel syndrome has a total bilirubin of 17.8 mg/dL and is receiving a standard multiple trace element additive (eg, MTE-5). What two trace elements should be monitored to avoid toxicity?

Copper and manganese. Both are excreted via the biliary tract. Copper and manganese levels should be monitored and these trace elements should be removed from the parenteral nutrition formula if serum or whole blood levels are increased. Copper and manganese should not empirically be removed from the parenteral nutrition solution because severe copper deficiencies have been reported when trace elements were removed without first checking for toxicity.

Image A 37-year-old man with newly diagnosed chronic intestinal pseudo-obstruction is sent home from the hospital on long-term parenteral nutrition. The parenteral nutrition provides a standard multivitamin additive and multiple trace element additive that provides zinc, copper, chromium, and manganese. Why is the patient at risk for cardiomyopathy?

Patients receiving long-term parenteral nutrition are at risk for selenium deficiency if selenium is not provided. Fatal cases of cardiomyopathy related to selenium deficiency have been reported in patients that did not receive selenium in the parenteral nutrition.

Image What trace mineral may be required in increased amounts when patients have persistent loss of small bowel fluids related to a fistula, short gut, or new ileostomy?

Zinc. Zinc losses in small bowel fluids are approximately 12 mg/L of small bowel fluid lost and can exceed the amount of zinc provided in a normal diet, tube feeding, or parenteral nutrition in patients with large volume losses.

Image What macromineral may need to be supplemented to standard tube feedings or parenteral nutrition if a patient has persistent large volume small bowel fluid losses related to a fistula or new ileostomy?

Sodium. All tube feedings and most standard parenteral nutrition solutions provide a limited amount of sodium, while jejunal and ileal fluid losses contain 100–120 mEq/L of sodium. Persistent large volume small bowel fluid losses can result in greater sodium loss than is provided with standard parenteral nutrition or enteral feeding formulas.

Image A 27-year-old woman with idiopathic gastoparesis who has been receiving jejunostomy feedings as the primary source of nutrition for 1 year begins to develop significant alopecia. What nutrient deficiencies should be suspected?

Iron and zinc are primarily absorbed in the proximal small bowel and patients on long-term enteral nutrition who bypasses the duodenum are at increased risk of deficiencies, which can result in alopecia. Iron and zinc compete for absorption; therefore, care should be taken to prevent iatrogenic deficiencies if supplemental doses of one or the other mineral are provided.

Image What macromineral deficiency can be anticipated in patient with a gastric outlet obstruction receiving jejunostomy feedings while continuously venting endogenous gastric secretions from a gastostomy?

Chloride. In a complete gastric outlet obstruction, patients will lose more chloride as hydrochloric acid than is provided with tube feedings, even while receiving a proton-pump inhibitor, due to the modest chloride provision in enteral nutrition formulas. Failure to provide additional chloride (generally as sodium chloride) with the feedings in the setting of persistent high-volume gastric fluid losses will result in metabolic alkalosis.

Image How many calories are there in a 500-mL container of 20% lipids? How much protein is in the bottle?

1000 calories. There is no protein.

Image True/False: A 20% lipid emulsion can be given through a peripheral intravenous line.

True. All intravenous lipids are isotonic.

Image What food allergies may serve as a contraindication to the use of parenteral lipid emulsions?

Severe egg or soy allergies.


Practical Gastroenterology Nutrition Series. Available at the University of Virginia Health System GI Nutrition Website:

Gottschlich MM, ed. The A.S.P.E.N. Nutrition Support Core Curriculum: A Case Based Approach—The Adult Patient. Silver Spring, MD: American Society for Parenteral and Enteral Nutrition; 2007.

Buchman AL, ed. Clinical Nutrition in Gastrointestinal Disease. Thorofare, NJ: SLACK Incorporated; 2006.