MKSAP quiz on nutrition

The following cases and commentary, which focus on inpatient nutrition, are excerpted from ACP's Medical Knowledge Self-Assessment Program (MKSAP 16).

Case 1: Nutrition for a burn patient

A 45-year-old woman is admitted to the intensive care unit after a motor vehicle accident in which she sustained significant burns to 70% of her body. She is intubated and sedated.

On physical examination, temperature is 37.9 °C (100.2 °F), blood pressure is 145/85 mm Hg, and her ventilated respiration rate is 15/min. She has extensive burns involving nearly all of the face, neck, and trunk, with notable extravasation of tissue fluid through her dressings.

Which of the following is the most desirable approach to nutritional support in this patient?

A. Enteral nutrition via nasogastric feeding tube
B. Enteral nutrition via percutaneous jejunal feeding tube
C. Parenteral nutrition via central access
D. Parenteral nutrition via peripheral access

View correct answer for Case 1

Case 2: Nutrition after colon resection

A 51-year-old man was admitted to the intensive care unit 3 days ago for septic shock with multisystem organ failure. Septic shock resulted from peritonitis following colon resection for a ruptured colonic diverticulum. He is on mechanical ventilation and had been treated with vasopressor agents, but these are no longer required. He is able to tolerate enteral nutrition with a standard commercial preparation (1 kcal/mL) at 10 mL/h via a soft nasogastric feeding tube.

On physical examination, temperature is 36.4 °C (97.5 °F), blood pressure is 120/70 mm Hg, pulse rate is 88/min, and respiration rate is 16/min. Weight is 80.0 kg (176.4 lb) and height is 177 cm (69.7 in).

Which of the following is the most appropriate next step in the management of this patient's nutrition?

A. Begin supplemental total parenteral nutrition
B. Change to an enhanced preparation of glutamine, arginine, antioxidants, and omega-3 fatty acids
C. Increase the rate of the current nutritional preparation
D. Supplement tube feeds with intravenous lipid formulation

View correct answer for Case 2

Case 3: Diarrhea after small-bowel resection

A 64-year-old man was admitted to the hospital 4 days ago for severe, acute abdominal pain and was found to have acute mesenteric ischemia. He underwent massive small-bowel resection, with 180 cm of small bowel remaining, and his colon was able to be salvaged. Over the past 4 days since surgery, he has been on parenteral nutrition with gradual progression of oral intake. He has significant diarrhea that wakes him up at night. He has been afebrile and has not had recurrent or worsening abdominal pain. His medications are low-dose low-molecular-weight heparin, ciprofloxacin, and metronidazole. He is also taking loperamide four times daily.

On physical examination, temperature is 36.2 °C (97.2 °F), blood pressure is 118/60 mm Hg, pulse rate is 68/min and regular, and respiration rate is 12/min. BMI is 25. Abdominal examination discloses a large scar from his recent surgery that is healing well. Bowel sounds are very active and there is mild tenderness throughout, as is expected postoperatively.

Laboratory studies, including serum electrolyte, glucose, and thyroid-stimulating hormone levels, are normal. Stool cultures and Clostridium difficile polymerase chain reaction are normal.

Which of the following is the most appropriate management?

A. Decrease the lipids in his parenteral nutrition
B. Increase the loperamide
C. Initiate cholestyramine
D. Initiate omeprazole
E. Stop oral intake

View correct answer for Case 3

Case 4: Nutritional status of an alcoholic patient

A 67-year-old man is admitted to the hospital after being found unresponsive and intoxicated at home. Family members report that he has a history of hypertension treated with atenolol and a history of alcoholism. He lives alone and has been resistant to assistance with meals and chores. He takes no other medication.

On physical examination, the patient is lethargic but arousable and smells strongly of alcohol. Vital signs are normal except for a pulse rate of 105/min. Mucous membranes are dry. No pain is elicited on abdominal examination. Chvostek sign and Trousseau phenomenon are noted.

After an electrocardiogram shows tachycardia (heart rate to 105/min) and a prolonged corrected QT interval (0.49 s), the patient is given intravenous fluids with added thiamine and folate. A calcium infusion is initiated.

Laboratory studies (before administration of thiamine, folate, and calcium) show amylase 110 units/L, blood urea nitrogen 33 mg/L (11.8 mmol/L), creatinine 1.4 mg/dL (124 µmol/L), ethanol 249 mg/dL (0.25 g/dL) (normal, <1.0 mg/dL [0.001 g/dL]), ionized calcium 2.9 mg/dL (0.7 mmol/L) (normal, 3.8-5.3 mg/dL [1.0-1.3 mmol/L]), and phosphorus 2.1 mg/dL (0.68 mmol/L).

In addition to the interventions already underway, measurement of which of the following serum levels is the most appropriate next diagnostic test?

A. Calcitonin
B. 1,25-Dihydroxyvitamin D
C. Magnesium
D. Parathyroid hormone

View correct answer for Case 4

Case 5: Paresthesia with history of malabsorption

A 54-year-old man is evaluated for a 9-month history of progressively worsening paresthesia in the legs that has recently spread to the hands and a 6-month history of an ataxic gait. The patient developed a malabsorption syndrome 3 years ago after gastric bypass surgery. He takes a daily multivitamin, iron, ascorbic acid, calcium, and vitamins D, B6, and B12.

On physical examination, temperature is 37.2 °C (99.0 °F), blood pressure is 110/60 mm Hg, and pulse rate is 70/min; BMI is 31. Neurologic examination shows decreased vibratory sensation in the hands and feet and decreased position sense in the feet. Hip flexion strength is 4/5 bilaterally, and reflexes are 3+ throughout with upgoing toes.

Laboratory studies show hemoglobin 12.9 g/dL (129 g/L), mean corpuscular volume 102 fL, vitamin B12 590 pg/mL (435 pmol/L) and rapid plasma reagin is nonreactive. T2-weighted MRIs of the cervical and thoracic spines show slight hyperintensity in the posterior columns from approximately C4 through T9 with no contrast enhancement.

Which of the following serum levels should be measured next?

A. Copper
B. Folate
C. 25-Hydroxyvitamin D
D. Thiamine
E. Vitamin A

View correct answer for Case 5

Answers and commentary

Case 1

Correct answer: A. Enteral nutrition via nasogastric feeding tube.

The most desired approach to nutritional support in this patient is to place a nasogastric feeding tube and initiate enteral nutrition. Patients with burns require many special nutritional considerations that are intended to supply the needs of their hypermetabolic state, prevent mucosal breakdown and infection in the gut, prevent the loss of lean body mass, and assist in wound healing. Enteral feeding through the stomach is preferred if it can be tolerated, as it maintains the integrity of the entire gastrointestinal tract by avoiding disuse atrophy. It is typically amenable to long-term use, which may be required during recovery from a severe burn injury. Most patients with burns, and even those with airway injury, can tolerate placement of an enteral feeding tube.

Although this patient's nutritional needs could likely be met with the use of a jejunal feeding tube, there is no clear indication for this intervention because the upper gastrointestinal system is not impaired, and this patient would benefit from continuing its use. Jejunal feeding systems are sometimes used in patients in whom there is concern about possible reflux and aspiration of gastric contents. However, no clear benefit of postpyloric tube placement has been shown in terms of either nutritional or reflux and aspiration outcomes. A percutaneous feeding tube carries a high risk of infection in a patient whose abdominal skin is not intact.

Total parenteral nutrition through central venous access is associated with high risk for infection, particularly in patients with extensive burn injuries. Other potential issues associated with central parenteral nutrition include maintenance of access, atrophy of the gastrointestinal tract, trace element deficiency, and high costs and maintenance requirements, particularly for long-term treatment. Thus, parenteral nutrition should only be given if enteral options have been tried and failed or were not tolerated.

Parenteral nutrition through peripheral access is limited in its nutritional value because of the difficulty in providing an adequate volume of high-concentration fluids through a noncentral catheter. In addition to access issues, infection risk, and costs, peripheral parenteral nutrition would likely not be adequate to meet this patient's increased nutritional needs associated with her burn injury.

Key Points

  • Enteral feeding is the desired means of nutritional support if it can be tolerated in most patients with critical illness; most patients with burns, and even those with airway injury, can tolerate placement of an enteral feeding tube.

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Case 2

Correct answer: C. Increase the rate of the current nutritional preparation.

The most appropriate next step in management is to increase the rate of the current nutritional preparation. The enteral route is generally well tolerated with a low complication rate. Because this patient has not demonstrated intolerance of enteral nutrition, the best management is to advance his enteral nutrition to goal. Enteral feeding should be initiated at an infusion rate of 15 to 30 mL/h and incrementally increased. Reasonable goals are 25 kcal/kg/d for calories and 2 g/kg/d for protein. The enteral feeding rate should be titrated to meet these needs given his increased metabolic requirements. There is consensus that nutritional support improves nutritional outcomes, such as body weight and mid-arm muscle mass. However, there is disagreement regarding whether nutrition improves important clinical outcomes, such as duration of mechanical ventilation, length of stay, and mortality rates. The goals of nutritional support include combating the adverse effects of malnutrition and modulating the underlying disease.

Parenteral nutrition is associated with more complications, particularly infectious complications, and has not been proved superior to enteral nutrition. Parenteral nutrition is indicated for patients in whom an enteral feeding trial fails or who have contraindications to enteral feeding.

Several nutrients, including glutamine, arginine, and omega-3 fatty acids (known as immunonutrition), influence immunologic responses. Use of immunonutrition is controversial, has not shown clear benefit, and is generally not recommended.

Use of a lipid suspension would increase calories delivered but would not be favorable to the nitrogen balance.

Key Points

  • When possible, enteral feeding is preferred over parenteral routes in critically ill patients.

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Case 3

Correct answer: D. Initiate omeprazole.

This patient should receive a proton pump inhibitor (PPI) such as omeprazole. In patients who have undergone massive resection of the small intestine and are left with short-bowel syndrome, there is a tremendous surge of gastric acid in the postoperative period. The increased acid can inactivate pancreatic lipase, leading to significant diarrhea and possible ulceration in the remaining bowel. Therefore, all patients who have undergone significant bowel resection should receive acid suppression therapy in the postoperative period with a PPI.

Decreasing the lipids in this patient's diet, rather than in his parenteral nutrition, may provide some clinical improvement, because oral long-chain triglycerides may not be handled well in the state of bile-salt deficiency and may result in diarrhea.

Although increasing the loperamide may help with diarrhea control, it will not target the underlying pathophysiology of the increased acid production and will not prevent small-bowel ulceration. Overlooking that point may lead to adverse consequences for this patient if his acid hypersecretion is not controlled.

Because this patient has had resection of such a large amount of small intestine, there is likely significant disruption of the enterohepatic circulation of bile with resulting bile salt deficiency. Giving this patient cholestyramine will bind the remaining bile salts that are present and worsen the diarrhea.

Stopping this patient's oral intake may lead to some improvement of his diarrhea; however, it is often not recommended if the patient is otherwise tolerating oral intake, because continued oral intake will allow for bowel adaptation over time.

Key Points

  • Patients who have undergone significant bowel resection should receive acid suppression therapy in the postoperative period owing to the acid hypersecretion that occurs.

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Case 4

Correct answer: C. Magnesium.

This patient should next have his serum magnesium level measured. He has a history of chronic alcohol abuse and serum chemistry results that are notable for hypocalcemia. Evidence of tetany and a corrected QT interval prolongation are indications for aggressive intravenous repletion of calcium. In this patient with alcohol abuse and symptomatic hypocalcemia, hypomagnesemia should be suspected. Hypomagnesemia in the setting of severe hypocalcemia should be treated promptly with intravenous magnesium to help increase serum calcium levels and prevent ventricular arrhythmias. In addition, hypomagnesemia can impair the ability to increase serum calcium levels because low levels of magnesium inhibit parathyroid hormone (PTH) secretion and induce resistance to PTH. Therefore, in addition to increasing the patient's serum calcium level, treatment of his hypomagnesemia is essential to restore normal parathyroid function.

Measurement of the serum calcitonin level is typically not helpful in the assessment of hypocalcemia because calcitonin plays only a minor role in calcium homeostasis in humans.

This patient most likely is vitamin D deficient because of poor nutrition associated with his alcohol abuse. Measurement of the serum 1,25-dihydroxyvitamin D level is unlikely to provide useful information regarding the exact cause of his hypocalcemia, and, in any case, measurement of the serum 25-hydroxyvitamin D level would be the more appropriate test.

The serum PTH level most likely would be inappropriately low in this patient as a result of his chronic alcohol abuse and hypomagnesemia. Measuring this level is thus unnecessary.

Key Points

  • Hypomagnesemia in the setting of severe hypocalcemia should be treated promptly with intravenous magnesium to help increase serum calcium levels and prevent ventricular arrhythmias.

Return to the next case

Case 5

Correct answer: A. Copper.

This patient's serum copper level should be measured next to detect copper deficiency. The Roux-en-Y gastric bypass is a dual-mechanism bariatric surgery combining a small gastric reservoir, which restricts oral intake, with a small-bowel bypass, which induces mild malabsorption. Nutritional deficiencies of vitamin B12, iron, calcium, folate, and 25-hydroxyvitamin D are common in patients after gastric bypass. Less frequently, deficiencies of magnesium, copper, zinc, vitamin A, other B-complex vitamins, and vitamin C may occur. This patient has a myelopathy (as evidenced by the hyperreflexia and upgoing toes) localizing to the posterior columns and bilateral corticospinal tracts. Common entities that cause dysfunction in this pattern are vitamin B12 deficiency, neurosyphilis, and copper deficiency. Copper deficiency causes a chronic syndrome similar to subacute combined degeneration and is also associated with macrocytic anemia. Therefore, this deficiency can be difficult to differentiate from vitamin B12 deficiency. Common causes are zinc toxicity, nutritional deficiency, or malabsorption syndrome, which is the likely cause in this patient.

Folate deficiency is not associated with myelopathy, and thus measuring the serum folate level in this patient would not be diagnostic.

Although low vitamin D levels have been associated with several conditions, including elevated risks for autoimmune disease, vitamin D deficiency itself is not causative of myelopathy.

Thiamine deficiency is associated with Wernicke-Korsakoff syndrome and not myelopathy. Therefore, obtaining the serum thiamine level would not help diagnose myelopathy.

Vitamin A deficiency can cause blindness, and hypervitaminosis A has been associated with benign idiopathic intracranial hypertension. However, alterations in the serum vitamin A level are not associated with myelopathy.

Key Points

  • Copper deficiency, which can be caused by zinc toxicity, nutritional deficiency, or malabsorption syndrome, can result in a myelopathy localizing to the posterior columns and bilateral corticospinal tracts.