Lorin Jbara 4th year Medical student Shaare Zedek medical center short bowel syndrome Lorin Jbara 4th year Medical student Shaare Zedek medical center

short bowel syndrome (SBS) The short bowel syndrome results from a total bowel length that is inadequate to support nutrition. 75% of cases occur from massive intestinal resection. SBS is the most common cause of intestinal failure.

causes Adults: mesenteric occlusion ,midgut volvulus, Traumatic disruption of the superior mesenteric vessels. Multiple sequential resections, most commonly associated with recurrent Crohn’s disease, account for 25% of patients. Infants and children: bowel resection secondary to necrotizing enterocolitis and congenital intestinal anomalies such as atresias or gastroschisis are the most common causes of SBS.

Signs and symptoms Abdominal pain Diarrhea and steatorrhea Fluid depletion Weight loss and malnutrition Fatigue

pathophysiology Several factors contribute to determining intestinal function including: 1) small intestine length 2) the site of intestinal resection 3) the presence or absence of the ileocecal valve 4) whether the colon is present 5) the gradual process of intestinal adaptation after surgical resection 6) intestinal motility.

Small intestinal length - The length of the small intestine is an important determinant of intestinal function. In infants: the normal length of the small intestine is approximately 125 cm . Infants with residual small intestine length of less than 75 cm are at risk for developing SBS. In adults: the normal length of the small intestine is approximately 480 cm. Adults with residual small intestine of less than 180 cm are at risk for developing SBS.

The site of intestinal resection- Jejunal resection:   The jejunum is the primary digestive and absorptive site for most nutrients. Thus, when the jejunum is resected, a temporary reduction in absorption of most nutrients occurs.

Ileal resection: Having residual ileum is advantageous because of its specialized functions: 1) Vitamin B12 absorption In adults, vitamin B12 malabsorption tends to occur if more than 60 cm of ileum is resected. 2) Bile acid absorption. * The diminished bile acid pool can further exacerbate malabsorption of fat and fat-soluble vitamins. * In addition, the increased passage of bile acids into the colon may induce a colonic secretory diarrhea. * Malabsorption of bile acids also causes excessive absorption of oxalate, leading to hyperoxaluria and possible kidney stone formation.

3) Ileal brake – Unabsorbed lipids reaching the ileum cause delay in gastric emptying (the “ileal brake”), which is beneficial because it facilitates absorption of nutrients within the small intestine. It is mediated by hormones secreted by the ileum including peptide YY. 4) Fluid absorption – The ileum normally reabsorbs a large portion of the fluid secreted by the jejunum during the digestive process. 5) Intestinal adaptation – The ileum has a greater capacity for intestinal adaptation as compared to the jejunum.

Loss of the ileocecal valve — The ileocecal valve is an important barrier to reflux of colonic material from the colon into the small intestine. It also helps to regulate the passage of fluid and nutrients from the ileum into the colon. Loss of the ileocecal valve can cause : 1) Reduction of small intestinal transit time, which impairs nutrient absorption. 2) Promotion of small bacterial overgrowth, which may cause malabsorption of vitamin B12, fats, and bile salts, causing diarrhea.

Loss of the colon : The colon has an important role in absorption of water, electrolytes and short chain fatty acids . Loss of the colon in combination with extensive small bowel resection is poorly tolerated and is likely to lead to dehydration and electrolyte depletion.

ILEAL ADAPTATION — The ileum has shorter villi and reduced surface area as compared to the jejunum. However, it is capable of undergoing marked adaptation after small bowel resection, with significant growth in villus surface area, as well as increases in intestinal length, diameter, and motor function . The mechanisms underlying intestinal adaptation are not fully understood, but it is clear that adaptation is strongly enhanced by the presence of nutrients in the gut lumen.

Nutrient effects: This effect is mediated by growth factors produced by the intestine as well as by functional and hormonal biliary and pancreatic secretions. The effects of various nutrients on intestinal adaptation have been studied in animals and humans. Arginine or citrulline: Studies in animal models suggest that supplementing citrulline in total parenteral nutrition can enhance intestinal adaptation. Glutamine – Parenteral supplementation of glutamine reversed intestinal hypoplasia in an animal model .

Triglycerides – In animal models, enteral supplementation with long-chain triglycerides appears to be more beneficial than medium-chain triglycerides in promoting overall intestinal adaptation, although medium chain triglycerides may be more easily absorbed .Human data is limited. Omega-3 fatty acids – Dietary fish oil, which is rich in omega- 3 fatty acids, appears to be beneficial in inducing adaptation in the small intestine and colon.

Gut hormones glucagon-like peptide 2 (GLP-2): a growth factor produced by the enteroendocrine L cells of the ileum and colon. Plasma concentrations of GLP-2 increase rapidly, and this induces adaptation in the remaining intestine . Exogenous administration of GLP-2 promotes adaptation and nutrient absorption in animal models of SBS. Studies in humans suggest that a teduglutide, a GLP-2 analog, promotes intestinal adaptation and absorption and has modest benefits in the treatment of SBS .

complicaTIONS Anemia Bacterial overgrowth in the small intestine Nervous system problems caused by a lack of vitamin B12 metabolic acidosis due to diarrhea Weakened bones (osteomalacia) Weight loss Increased incidence of gallstone due to disruption of the enterohepatic circulation and of nephrolithiasis from hyperoxaluria. Nutrient deficiency: Iron, magnesium, zinc, copper and vitamins - A,D,E,K,B12

Laporatory tests Blood chemistry tests Complete blood count (CBC) Vitamin levels in the blood Fecal fat test Small intestine x-ray CT

TREATMENT Prevention: Preventing unnecessary extensive resection of the bowel. After massive small bowel resection, the treatment course may be divided into early and late phases. Early phase: treatment is primarily directed at the control of diarrhea, replacement of fluid and electrolytes and prompt institution of TPN.(fluid replacement protocols with sodium, potassium chloride, and magnesium).

Late phase: enteral nutrition- the most common types of enteral diets are elemental(vivonex, flexical) or polymeric(Isocal, Ensure). Oxalate restriction is important in those with an intact colon. Oral electrolyte solutions Vitamins, especially fat soluble vitamins, as well as calcium, magnesium and zinc supplementation should be provided. The important elements of chronic enteral nutrition are: * Small frequent feedings (every two to three hours in adults). * A reasonable mixture of protein, carbohydrates and fats. * Avoidance of hypertonic beverages (eg, sodas and fruit juices). * Avoidance of high carbohydrate feedings.

Pharmacologic therapy : H2 blockers, proton pump inhibitors, and octreotide inhibit excessive gastric or pancreatic secretion with varying success. - Loperamide often results in a decrease in stool output and may be useful in patients without small bowel bacterial overgrowth. Growth factors — Growth factors have been tried to hasten adaptation and to enhance mucosal growth beyond the normal limits of adaptation: *Glucagon-like peptide-2 *Teduglutide *Glutamine and growth hormone

Surgical procedures: *Procedures designed to slow small intestinal transit include reversed segments of bowel or colon interpositioned to slow the delivery of nutrients through the small intestine, and creation of valves that produce a partial obstruction to disrupt the normal flow of contents. Procedures to slow transit are contraindicated in small children and patients with small bowel bacterial overgrowth.

Surgical procedures to lengthen dilated bowel include : Bianchi procedure : the bowel is cut in half and one end is sewn to the other.

Serial transverse enteroplasty (STEP): where the bowel is cut and stapled in a zigzag pattern: * transecting the bowel longitudinally. * preserving the blood supply to both sides of the small intestine. * creating a segment of bowel twice the length and half the diameter of the original segment.

Small bowel transplantation Small bowel transplantation has been advocated for certain patients with short bowel syndrome : - who have developed complications from long-term parenteral nutrition . - whom adequate adaptation cannot occur.

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