Short Bowel Syndrome

Etiology

SBS can result from extensive surgical resection or congenital intestinal diseases. The most common pathologies that lead to SBS in adults are Crohn disease, mesenteric ischemia, radiation enteritis, post-surgical adhesions, and post-operative complications. In children, the most common pathologies include volvulus, intestinal malformations, and necrotizing enterocolitis.[1]

Epidemiology

The epidemiology of SBS is not well-delineated as there are no data on the frequency of intestinal failure secondary to SBS.

Pathophysiology

SBS can be classified by anatomical, pathophysiological, and postoperative criteria. Anatomically, there are three types of SBS: end-jejunostomy, jejunocolonic anastomosis where the jejunum is in continuity, most commonly, with the left colon, and jejunoileal anastomosis. The pathophysiological criteria can also be subdivided into categories where the colon is in continuity and those where it is not.

The primary pathophysiological mechanism of chronic intestinal failure secondary to SBS is intestinal malabsorption due to the loss of intestinal absorptive surface and more rapid intestinal transit. The successful rehabilitation of a patient with SBS depends upon the management of the three phases of SBS: acute phase, adaptation phase, and maintenance phase.

The acute phase of SBS lasts 3 to 4 weeks and involves metabolic derangement and significant intestinal losses as well as gastric hypersecretion due to the lack of inhibitory hormones that are normally released from the terminal ileum. It requires close monitoring in the hospital setting to avoid sequelae such as dehydration with acute kidney failure, acid-base abnormalities, and electrolyte deficiencies.

The adaptation phase of SBS lasts 1 to 2 years and involves adaptive changes of remaining small bowel to increase the area of bowel available for nutrient absorption, slow down intestinal transit to maximize the time available for absorption, and adaptive hyperphagia. These processes are promoted by the presence of nutrients in the bowel, pancreatic and biliary secretions, and hormones released by the ileum and colon. Chronic intestinal failure – the condition that exists when the adaptation phase fails to occur – is more likely to be reversible in the following situations:

• When there are more than 35 centimeters of small bowel along with a jejunoileal anastomosis and an intact ileocecal valve and colon
• When there are more than 60 centimeters of small bowel with a jejunocolonic anastomosis
• When there is more than 115 centimeters of small bowel with an end jejunostomy

The third and final phase of SBS is the maintenance phase. This phase is managed with special diets, oral or intramuscular supplementation of nutrients, and pharmacological treatments.[1]

Histopathology

Intestinal failure-associated liver disease is a complication of SBS. Histopathological findings include cholestasis, steatosis, steatohepatitis, ductopenia, and perivenular and portal fibrosis.

History and Physical

The primary adverse outcome of SBS is malabsorption secondary to decreased intestinal absorptive surface area and rapid intestinal transit. The most common signs, symptoms, and findings include malnutrition, weight loss, diarrhea, steatorrhea, dehydration, vitamin deficiencies, and electrolyte imbalance. The individual with SBS will likely have undergone extensive small bowel resection related to one of the underlying pathologies listed above.[1]

Treatment / Management

Initial management of SBS involves maintaining good nutritional status, maximizing the absorptive surface area of the remaining intestine, and preventing complications. This involves early postoperative parenteral nutrition as well as enteral nutrition once the patient's ileus has resolved. This promotes intestinal adaptation which improves absorption of nutrients over time.

Those patients in whom intestinal failure is irreversible will require either lifelong home parenteral nutrition or intestinal transplantation if a life-threatening complication of either SBS or home parenteral nutrition arises. Treatment of SBS, therefore, largely consists of managing and preventing complications that arise as a direct result of SBS or secondarily to home parenteral nutrition. The management of SBS and the prevention of its complications share many of the same treatments.

• Intestinal failure-associated liver disease and liver cholestasis are treated with maintaining some oral feeding, promptly treating infection or inflammation, optimizing home parenteral nutrition, decreasing dependence on soy-based lipid emulsions or switching them to fish oil-based emulsions and non-transplant surgical procedures.
• SBS patients with less than 180 centimeters of small bowel or an absent ileocecal valve are at increased risk of developing gallstones, frequently composed of calcium bilirubinate. These gallstones can be prevented or reversed by maintaining enteral feeding and limiting periods of oral fasting and by limiting the use of narcotic and anticholinergic medications.
• Dehydration, hyponatremia, chronic renal failure, and nephrolithiasis secondary to SBS are managed with intravenous supplementation of fluids to maintain normal hydration and urinary flow. More specifically, the treatment of dehydration and hyponatremia in patients with SBS should maintain normal hydration with a urine output of 800 milliliters per day and urine sodium greater than 20 millimoles/liter.
• Hypomagnesemia can be caused by malabsorption of magnesium due to loss of the distal ileum and right colon as well as chelation with fatty acids. Treatment consists of appropriate hydration as delineated above and magnesium supplementation to a level greater than 1.5 milligrams/deciliter.
• D-lactic acidosis with an increased anion gap can occur in patients with SBS due to the fermentation of unabsorbed carbohydrates by colon microbiota. This can lead to a D-lactate encephalopathy that presents with slurred speech, ataxia, altered mental status, psychosis, and sometimes coma. D-lactic acidosis is primarily a clinical diagnosis. Treatment includes cessation of enteral feeds with carbohydrates, administration of an antibiotic active against D-lactate forming bacteria, appropriate hydration, and thiamine supplementation. Antibiotics include metronidazole, vancomycin, clindamycin, neomycin, and tetracyclines.
• Almost all patients on long-term home parenteral nutrition have metabolic bone disease that manifests as osteopenia, osteomalacia, or osteoporosis. Diagnosis and evaluation are done with mineral bone density, serum and urine mineral levels, vitamin D, PTH, and markers of bone turnover. Management includes lifestyle and dietary changes, treatment of underlying disease, optimization of vitamin D status and parenteral nutrition, and sometimes bisphosphonates.

Surgical management is another important treatment strategy available to patients with SBS. Patients on parenteral nutrition who suffer from rapid transit may benefit from reversing intestinal segments or interposing segments of colon into the small bowel. Those with less than 60 centimeters of small bowel and parenteral nutrition-related complications may be candidates for intestinal transplantation. Patients with dilated bowel secondary to obstruction can sometimes be treated with intestinal tapering or strictureplasty if they have a bowel remnant greater than 120 centimeters or tapering with lengthening if the remnant is less 90 centimeters in adults or less than 30 centimeters in children.[1][3][4]

Differential Diagnosis

• Antral G Cells Hyperplasia

• Atrophic Gastritis

• Gastric Outlet Obstruction

• Gastrinoma

• Previous Vagotomy

• Renal Failure

• Retained Antrum Syndrome

• Short Gut Syndrome

Prognosis

Those with greater than 180 cm of small bowel generally require no parenteral nutrition. Those with greater than 90 cm will usually require it for less than 1 year. And those with less than 60 cm will likely require lifetime parenteral nutrition.

Complications

The primary complications of malabsorption are malnutrition, weight loss, steatorrhea, diarrhea, electrolyte imbalance, and vitamin deficiencies. Other complications include nephrolithiasis due to hyperoxaluria, cholelithiasis, transient gastric hypersecretion, bacterial overgrowth, dehydration, hyponatremia, potassium deficiency, magnesium deficiency, renal failure, calcium oxalate kidney stones, cholestasis secondary to intestinal failure-associated liver disease, gallstones, and d-lactic acidosis.

In adults and older children, steatosis is more common, whereas in infants cholestasis and rapid progression to liver fibrosis is the more common progression. Intestinal failure-associated liver disease deaths are seen in between 16% and 60% of deaths in infants on home parenteral nutrition.[1]