Short Bowel Syndrome
Short bowel syndrome is a malabsorption disorder.
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 B12 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 B12 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 calcium and magnesium). An oral iso-osmotic solution of sodium and glucose (similar to the World Health Organization's oral rehydration formula—see Oral Rehydration) 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 hour 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 B12 should be given to patients with a documented deficiency. Most patients should take supplemental vitamins, calcium, and magnesium.
Gastric acid hypersecretion can develop, which can deactivate pancreatic enzymes; thus, most patients are given H2 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.
Adult patients who require parenteral support may benefit from teduglutide (a glucagon-like peptide-2 [GLP-2] analog). The recommended dosage is 0.05 mg/kg body weight subcutaneously once/day.
Extensive resection or loss of small bowel can cause significant diarrhea and malabsorption.
Patients with < 100 cm of remaining jejunum require lifelong total parenteral nutrition; patients with > 100 cm of remaining 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.