Test yourself: Nutrition

The following cases and commentary, which address nutrition, are excerpted from ACP's Medical Knowledge Self-Assessment Program (MKSAP14).

Case 1: Acute respiratory failure

A 79-year-old man who lives in a nursing home is admitted to the intensive care unit with acute respiratory failure. Chest radiograph shows a right lower lobe infiltrate. He is intubated emergently and placed on mechanical ventilation. His temperature on admission to the ICU is 39.6°C (103.4°F); the leukocyte count is 18,000/µL (18.9 × 109/L), and the serum albumin is 2.2 g/dL. The decision is made to place a duodenal feeding tube and initiate enteral tube feedings. The patient weighs 70 kg (154 lb) and is 157 cm (62 in) tall.

Which of the following is the most appropriate daily nutritional support for this patient?

A. 2500 kcal and 140 g protein.
B. 1800 kcal and 100 g protein.
C. 1200 kcal and 140 g protein.
D. 1200 kcal and 120 g protein.

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Case 2: Severe upper abdominal pain

A 54-year-old woman is hospitalized because of acute severe upper abdominal pain and vomiting. Studies confirm acute pancreatitis, most likely gallstone-related. Twelve hours after admission, the patient develops respiratory distress and is transferred to the ICU for mechanical ventilation. Laboratory studies in the ICU show the following: leukocyte count, 8500/µL (8.5 × 109/L); serum calcium, 7.6 mg/dL (1.9 mmol/L); serum creatinine, 1.9 mg/dL (168 µmol/L); serum total bilirubin, 0.9 mg/dL (15.39 µmol/L); serum aspartate aminotransferase, 438 U/L; serum alkaline phosphatase, 120 U/L; serum lactate dehydrogenase, 410 U/L.

Nasogastric suction is initiated, and imipenem is begun. An abdominal CT scan with contrast shows that approximately 50% of the pancreas is necrotic. Gallstones are also seen. There is no bile duct dilatation.

After three days, the patient is extubated and transferred from the ICU. She continues to have a low-grade fever. Laboratory values return to normal except for a leukocyte count of 11,600/µL (11.6 × 109/L) with a normal differential. Although her nasogastric tube is not removed, the patient continues to have abdominal pain and nausea. She has been receiving only intravenous fluids since admission.

Which of the following is the most appropriate form of nutrition for this patient at this time?

A. Nasogastric tube feedings as tolerated.
B. Complete total parenteral nutrition.
C. Total parenteral nutrition; withhold lipids.
D. Enteral hyperalimentation via the jejunum.

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Case 3: Postprandial abdominal pain and diarrhea

A 52-year-old man has a several-year history of postprandial abdominal pain and diarrhea that have recently increased. The patient describes the pain as a crampy sensation in the upper abdomen that occurs approximately 15 to 20 minutes after meals, is accompanied by nausea, and is followed by loose stools, lightheadedness and diaphoresis. He has not had fever or chills. Over-the-counter antacids are ineffective. The patient underwent partial gastrectomy with vagotomy and a Billroth II anastomosis 15 years ago for severe peptic ulcer disease. He is otherwise healthy, and his only medication is a daily multivitamin.

On physical examination, the patient is thin and has a well-healed midline abdominal scar. Abdominal examination discloses slight epigastric tenderness to palpation. The remainder of the examination is normal.

Which of the following is the most appropriate treatment at this time?

A. Enteral supplements.
B. A gluten-free diet.
C. A proton pump inhibitor.
D. Metoclopramide.
E. Six small meals daily.

View correct answer for Case 3

Answers and commentary

Case 1

Correct answer: B. 1800 kcal and 100 g protein.

Malnutrition impairs wound healing and immunologic function, and increases infection and mortality rates. Patients in the intensive care unit generally require 25 to 30 nonprotein kcal/kg/d and 1.0 to 1.5 protein kcal/kg/d to meet the energy expenditures associated with critical illness. This patient should receive approximately 1800 kcal (25 nonprotein kcal/kg/d) and 100 g protein (1.5 protein kcal/kg/day). The oral or enteral route of feeding is preferred. If there is an aspiration risk, a feeding tube should be placed in the small intestine. Continuous enteral feedings decrease the risk of aspiration.

Albumin and prealbumin levels are indicators of visceral protein status. Albumin has a half-life of approximately 20 days. When albumin values are below normal levels, a sizable amount of the serum pool has been lost. Generally, albumin is considered a late indicator of malnutrition. Prealbumin's short half-life of two days and small serum pool allow small changes in nutritional status to be identified in a short time frame. Low prealbumin levels result from either inadequate nutrition or inflammatory stress. Prealbumin levels <5 mg/dL indicate severe protein and calorie malnutrition. Prealbumin should be used as an indicator of nutritional improvement and as a measure of how well nutritional interventions are working. Prealbumin can be measured once or twice per week and used as a sensitive monitor of nutritional progress.

Key points

  • Patients in the intensive care unit generally require 25 to 30 nonprotein kcal/kg/d and 1.0 to 1.5 protein kcal/kg/d to meet the energy expenditures associated with critical illness.

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Case 2

Correct answer: D. Enteral hyperalimentation via the jejunum.

This patient presents with severe acute pancreatitis, presumably gallstone-related. She also has multisystem disease as evidenced by respiratory failure and mildly impaired renal function. A CT scan shows significant pancreatic necrosis, which is a poor prognostic sign. Enteral alimentation is the most appropriate form of nutrition for this patient. In addition, feedings into the proximal small bowel through a jejunal feeding tube have been shown to decrease the rate of infections in patients with severe acute pancreatitis without exacerbating the pancreatitis.

Because of her nausea and severe pancreatitis, she is unlikely to tolerate nasogastric tube feedings, but this route would be a reasonable option in the absence of persistent nausea and vomiting. Parenteral nutrition may be required if enteral feedings are poorly tolerated, but the enteral route is preferred initially. Although hypertriglyceridemia may occur in patients with acute pancreatitis, intravenous lipids can be provided when using total parenteral nutrition.

Key points

  • Patients with severe, acute pancreatitis require enteral, rather than parenteral, nutrition.

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Case 3

Correct answer: E. Six small meals daily.

The patient's clinical presentation is consistent with dumping syndrome, which can occur in up to 20% of patients who have undergone partial gastrectomy with vagotomy. Dumping may be classified as either early phase or late phase. Early-phase dumping occurs shortly after eating and is associated with abdominal pain caused by rapid emptying of gastric contents into the duodenum. This leads to acute distention and nausea followed by diarrhea. Late-phase dumping is due to a vasomotor complex consisting of lightheadedness and diaphoresis that may start 90 minutes to three hours after eating. Patients with dumping syndrome should initially be treated conservatively with a diet consisting of six small meals daily. They should not eat meals rich in simple carbohydrates and should avoid drinking liquids for 10 to 15 minutes after eating solid foods.

Enteral supplements may lead to worsening symptoms because of the concentrated carbohydrates contained in these supplements. A gluten-free diet is used for treating celiac sprue, which this patient does not have. Proton pump inhibitors will be ineffective because the patient does not have dyspepsia. His symptoms are not consistent with gastroparesis; therefore, a promotility agent such as metoclopramide is not indicated.

Key points

  • Patients who have undergone gastrectomy may develop dumping syndrome, which is characterized by nausea, abdominal pain and distention, lightheadedness and diaphoresis.
  • Patients with dumping syndrome should initially be treated conservatively with a diet consisting of six small meals daily.