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Short Bowel Syndrome
Short bowel syndrome is malabsorption resulting from extensive resection of the small bowel (usually more than two thirds the length of the small intestine). Symptoms depend on the length and function of the remaining small bowel, but diarrhea can be severe, and nutritional deficiencies are common. Treatment is with small feedings, antidiarrheals, and sometimes TPN or intestinal transplantation.
Common reasons for extensive resection are Crohn disease, mesenteric infarction, radiation enteritis, cancer, volvulus, and congenital anomalies.
Because the jejunum is the primary digestive and absorptive site for most nutrients, jejunal resection leads to loss of absorptive area and significantly reduces nutrient absorption. In response, the ileum adapts by increasing the length and absorptive function of its villi, resulting in gradual improvement of nutrient absorption.
The ileum is the site of vitamin B 12 and bile acid absorption. Severe diarrhea and bile acid malabsorption result when > 100 cm of the ileum is resected. Notably, there is no compensatory adaptation of the remaining jejunum (unlike that of the ileum in jejunal resection). Consequently, malabsorption of fat, fat-soluble vitamins, and vitamin B 12 occurs. In addition, unabsorbed bile acids in the colon result in secretory diarrhea. Preservation of the colon can significantly reduce water and electrolyte losses. Resection of the terminal ileum and ileocecal valve can predispose to bacterial overgrowth.
In the immediate postoperative period, diarrhea is typically severe, with significant electrolyte losses. Patients typically require TPN and intensive monitoring of fluid and electrolytes (including Ca and Mg). An oral iso-osmotic solution of Na and glucose (similar to WHO oral rehydration formula—see Practical Example : Solutions) is slowly introduced in the postoperative phase once the patient stabilizes and stool output is < 2 L/day.
Patients with extensive resection (< 100 cm of remaining jejunum) and those with excessive fluid and electrolyte losses require TPN for life.
Patients with > 100 cm of remaining jejunum can achieve adequate nutrition through oral feeding. Fat and protein in the diet are usually well tolerated, unlike carbohydrates, which contribute a significant osmotic load. Small feedings reduce the osmotic load. Ideally, 40% of calories should consist of fat.
Patients who have diarrhea after meals should take antidiarrheals (eg, loperamide) 1 h before eating. Cholestyramine 2 to 4 g taken with meals reduces diarrhea associated with bile acid malabsorption due to ileal resection. Monthly IM injections of vitamin B 12 should be given to patients with a documented deficiency. Most patients should take supplemental vitamins, Ca, and Mg.
Gastric acid hypersecretion can develop, which can deactivate pancreatic enzymes; thus, most patients are given H 2 blockers or proton pump inhibitors.
Small-bowel transplantation is advocated for patients who are not candidates for long-term TPN and in whom adaptation does not occur.
Extensive resection or loss of small bowel can cause significant diarrhea and malabsorption.
Patients with < 1 m of jejunum require lifelong TPN; patients with > 1 m of jejunum may survive on small feedings that are high in fat and protein and low in carbohydrate.
Antidiarrheals, cholestyramine, proton pump inhibitors, and vitamin supplements are needed.
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