Short Bowel Syndrome

Short bowel syndrome is a malabsorptive condition most commonly associated with extensive intestinal resection for etiologies such as Crohn’s disease, bowel obstruction, trauma, radiation therapy, and vascular insufficiency. The short length of bowel results in insufficient surface area for fluid and electrolyte absorption. Patients typically present with diarrhea, electrolyte abnormalities, and dehydration. Management options include antimotility agents, antisecretory agents, and total parenteral nutrition for patients who cannot maintain themselves with oral intake. Last-resort options include surgical intestinal lengthening procedures and small bowel transplant.

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Overview

Definition

  • Short bowel syndrome (SBS) is a malabsorptive condition due to the insufficient length of functional small intestine. The condition leads to diarrhea, malnutrition, and dehydration. 
  • Intestinal failure is reduced GI function that cannot meet the minimum requirements for absorption of electrolytes, water, and macronutrients.
    • May be permanent or transient
    • Caused by SBS, intestinal dysmotility, small bowel mucosal disease, mechanical obstruction, or intestinal fistula
    • Results in dependence on supplemental IV nutrition and hydration

Epidemiology

  • Rare condition
  • Incidence and prevalence are difficult to estimate.
  • Approximately 10,000–20,000 individuals in the United States are on total parenteral nutrition (TPN) due to SBS.

Etiology

  • Surgical resection of the small intestine
    • Adults:
      • Mesenteric ischemia
      • Trauma
      • Bowel obstruction
    • Pediatric population:
      • Necrotizing enterocolitis
      • Intestinal atresia
      • Midgut volvulus with ischemia
  • Functional disorder of the intestine
    • Crohn’s disease
    • Radiation enteritis
  • Congenital short bowel (rare)

Pathophysiology

Physiology

  • Jejunum:
    • Primary digestive and absorptive site
    • Contains:
      • ↑ Concentration of transport carrier proteins
      • Concentrated digestive enzymes
      • Long villi with ↑ absorptive surface
  • Distal ileum: 
    • Reabsorbs bile acids 
    • Vitamin B12 absorption
  • Colon:
    • Participates in absorption of water and electrolytes
    • Metabolizes undigested carbohydrates to short-chain fatty acids for absorption

Consequences of bowel resection

Several factors determine the degree of intestinal function loss after bowel resection:

  • The length of remaining small bowel after resection:
    • Normal length of the small intestine is 480 cm (190 in).
    • < 180–200 cm (71–79 in) places a patient at very high risk for SBS
  • Segments of small bowel removed:
    • Jejunocolic anastomosis
      • Resection of the entire ileum and ileocecal valve
      • Most common anatomy in SBS
    • Jejunoileocolonic anastomosis:
      • Resection of a portion of the ileum
      • Maintains the ileocecal calve and entire colon
      • Best prognosis → avoids TPN in many cases
    • End jejunostomy:
      • Resection of ileum, ileocecal valve, and colon (or colon is present but disconnected)
      • Worst prognosis → often results in TPN dependence
  • Loss of the ileocecal valve:
    • ↑ In bile acids entering the colon → stimulates colonic fluid and electrolyte secretion → ↑ diarrhea
    • Malabsorption of vitamin B12
  • Concomitant colon resection:
    • Colon helps mitigate fluid loss.
    • Loss of the colon → ↓ adaptive capabilities
Types of bowel resection

Types of bowel resection

Image by Lecturio.
Radiological examinations demonstrated the short bowel syndrome

Radiological examinations demonstrating short bowel syndrome

Image: “Colectomy and acute renal failure: a case report with unusual presentation” by Sahin OZ, Bilir C, Ayaz T. License: CC BY 3.0, edited by Lecturio.

Phases of SBS

Acute phase:

  • Begins immediately following resection or insult to the bowel
  • Lasts 3‒4 weeks
  • Characteristics:
    • ↓ Inhibitory hormones from the terminal ileum → gastric acid hypersecretion
      • ↑ Fluid volume entering the small bowel
      • ↑ Acid load
    • Significant intestinal fluid losses → dehydration and electrolyte deficiencies
    • Poor absorption of all nutrients

Adaptation phase:

  • Begins 2‒4 days after insult to bowel
  • Lasts 1‒2 years
  • Structural and functional changes to the small bowel and colon occur to maximize absorption.
    • .Jejunum demonstrates some adaptive changes.
      • Functional changes in transport and enzymatic activity
      • Minimal structural changes
    • Ileum is the most capable of adaptation.
      • ↑ In villous length and surface area
      • ↑ Intestinal length and diameter
      • Slowed motility
    • Colonic adaptation
      • ↑ In number of enterocytes
      • Slowed motility
      • ↑ Absorption of fluids → can absorb up to 6 L per day
      • ↑ Carbohydrate reabsorption to maintain approximately 50% of daily energy requirements

Maintenance phase:

  • Permanent
  • Bowel reaches its maximum absorptive capacity.

Clinical Presentation and Diagnosis

General clinical presentation

  • History of bowel resection, inflammatory bowel disease, or radiation
  • Symptoms:
    • Diarrhea
    • Steatorrhea
    • Weight loss
    • Fatigue
    • Heartburn
    • Lower extremity swelling
  • Physical exam findings
    • Dehydration
    • Temporal wasting
    • Loss of muscle mass

Nutritional deficiencies

  • Essential fatty acid deficiency
    • Growth retardation
    • Dermatitis
    • Alopecia
  • Vitamin A deficiency
    • Xerophthalmia 
      • Abnormal dryness of the conjunctiva and cornea
      • Thickening of the conjunctiva
      • Can lead to corneal ulcerations
      • Eventual night blindness or total blindness
    • Dry, scaly skin
    • Growth delay
    • Immune system impairment
  • Vitamin D deficiency
    • Poor growth
    • Osteomalacia
    • Rickets in children
  • Vitamin E deficiency
    • Ataxia
    • Hemolytic anemia
    • Immunodeficiency
  • Vitamin K deficiency
    • Ecchymoses
    • Bleeding gums
    • Petechia
  • Vitamin B12 deficiency
    • Pernicious anemia
    • Ataxia
    • Paresthesias
  • Mineral deficiencies
    • Copper
    • Zinc
    • Selenium
    • Iron
  • Electrolyte deficiencies
    • Potassium
    • Magnesium
    • Calcium
    • Bicarbonate

Laboratory findings

The following table summarizes possible laboratory findings in SBS that correlate with signs and symptoms of malabsorption.

ManifestationLaboratory findings
Steatorrhea↑ Fecal fat content
Diarrhea↑ Stool osmolality
Bleeding, ecchymosis↑ PT/INR and aPTT
Microcytic anemia↓ Ferritin and iron
Macrocytic anemia↓ Vitamin B12 and folic acid
Bone pain, fractures↓ Calcium and vitamin D
Lactose intoleranceAbnormal lactose tolerance test
Edema↓ Serum albumin and prealbumin

Management

Acute phase

  • Goal: Stabilize fluid and electrolyte losses.
  • IV fluids and electrolyte replacement
  • Gastric acid suppression
    • Histamine blockers (H2 blockers)
    • Proton pump inhibitors (PPIs)
  • TPN
    • Start once patient is stabilized.
    • Helps maintain hydration
    • Requires close monitoring and adjustments for:
      • Electrolytes
      • Fat
      • Carbohydrates
      • Protein
      • Vitamins
      • Minerals
  • Enteral nutrition
    • Can be done through a nasogastric or gastrostomy feeding tube
    • Should be initiated as soon as possible
    • Goal is to facilitate intestinal adaptation and reduce the need for TPN.

Adaptation phase

  • Slow transition to an oral diet
  • Continue gastric acid suppression for the first 6 months.
  • Antimotility agents to prolong transit time
    • Loperamide (Immodium)
    • Diphenoxylate-atropine (Lomotil)
    • Tincture of opium
  • Decrease GI secretions
    • Octreotide (somatostatin analog) inhibits GI secretions. 
    • Cholestyramine to bind bile acids
  • Teduglutide (Gattex)
    • Analog of glucagon-like peptide 2
    • Promotes small bowel adaptation
    • Used in patients with persistent intestinal failure requiring TPN

Surgical interventions

Intestinal lengthening procedures:

  • Most commonly performed in pediatric populations, rarely in adults
  • Indicated in patients with persistent intestinal failure who meet specific criteria:
    • Dilated small bowel
    • Failure of maximal medical therapy
    • Reasonable chance that length of reconstructed bowel will liberate the patient from TPN dependence
    • No preexisting motility disorders
  • Techniques:
    • Longitudinal intestinal lengthening and tailoring (LILT) procedure
      • Dilated small bowel is transected longitudinally between the mesenteric and antimesenteric border to create parallel segments.
      • Requires multiple small bowel anastomoses
    • Serial transverse enteroplasty procedure (STEP)
      • Increases length and absorptive capacity by tapering dilated bowel
      • No small bowel anastomoses

Transplant:

  • Very rarely performed due to success with medical therapies and lengthening procedures
  • Often done at the same time as solid organ transplant (multivisceral transplantation)
  • Reserved for patients who are dependent on TPN with the following additional complications:
    • Hepatic failure (most common cause of death in SBS)
    • Thrombosis of major central veins prohibiting central line placement
    • Recurrent catheter-related sepsis
    • Recurrent, severe dehydration despite TPN

Differential Diagnosis

  • Crohn’s disease: a chronic, recurring condition that causes patchy, transmural inflammation involving any part of the GI tract (most commonly terminal ileum and colon). Patients present with intermittent, non-bloody diarrhea and crampy abdominal pain. Extraintestinal manifestations may include uveitis, gallstones, erythema nodosum, and arthritis. Diagnosis is established via endoscopy with biopsy, and management includes corticosteroids, azathioprine, antibiotics, and anti-tumor necrosis factor (TNF) agents.
  • Celiac disease: an autoimmune reaction to gliadin, a component of gluten. The immune response is localized to the proximal small intestine and causes the characteristic histologic findings of villous atrophy, crypt hyperplasia, and intraepithelial lymphocytosis. Patients present with diarrhea and symptoms related to malabsorption (steatorrhea, weight loss, and nutritional deficiencies). Diagnosis is made by serological antibody testing and confirmed by small intestine biopsy. Management requires a lifelong gluten-free diet.
  • Necrotizing enterocolitis: most commonly occurs in premature infants who are formula-fed and is characterized by ischemic necrosis of the intestinal mucosa. Individuals present with abdominal distention, vomiting, abdominal tenderness, and rectal bleeding. The diagnosis is primarily made with imaging, such as abdominal X-ray or ultrasound. Treatment options consist of conservative management with bowel rest and antibiotics, or surgery in cases of known or suspected necrosis with perforation.
  • Small intestinal bacterial overgrowth: occurs when aerobic and anaerobic microbes normally present in the colon grow excessively in the small intestine. More than 90% of cases are due to motility disorders and chronic pancreatitis. Patients present with bloating, flatulence, watery diarrhea, and abdominal discomfort. The diagnosis can be made with breath testing. The mainstay of treatment is antibiotics and correction of nutritional deficiencies.

References

  1. DiBaise, J.K. (2020). Management of the short bowel syndrome in adults. In Grover, S. (Ed.), UpToDate. Retrieved February 20, 2021, from https://www.uptodate.com/contents/management-of-the-short-bowel-syndrome-in-adults
  2. Cagir, B. (2021). Short-Bowel Syndrome. In Geibel, J. (Ed.), Medscape. Retrieved February 20, 2021, from https://emedicine.medscape.com/article/193391-overview
  3. DiBaise, J.K. (2020). Pathophysiology of short bowel syndrome. In Hoppin, A.G. (Ed.), UpToDate. Retrieved February 21, 2021, from https://www.uptodate.com/contents/pathophysiology-of-short-bowel-syndrome
  4. Khanm F.A., Selvaggi, G. (2020). Overview of intestinal and multivisceral transplantation. In Robson, K.M. (Ed.), UpToDate. Retrieved February 21, 2021, from https://www.uptodate.com/contents/overview-of-intestinal-and-multivisceral-transplantation
  5. Stamm, D.A., Duggan, C. (2020). Management of short bowel syndrome in children. In Hoppin, A.G. (Ed.), UpToDate. Retrieved February 21, 2021, from https://www.uptodate.com/contents/management-of-short-bowel-syndrome-in-children
  6. Kim, J.H. (2020). Neonatal necrotizing enterocolitis: Clinical features and diagnosis. In Kim, M.S. (Ed.), UpToDate. Retrieved February 21, 20210, from https://www.uptodate.com/contents/neonatal-necrotizing-enterocolitis-clinical-features-and-diagnosis
  7. Pimental, M. (2020). Small intestinal bacterial overgrowth: Management. In Grover, S. (Ed.), UpToDate. Retrieved February 21, 2021, from https://www.uptodate.com/contents/small-intestinal-bacterial-overgrowth-management
  8. Ruiz, Jr., A.R. (2021). Short bowel syndrome. MSD Manual Professional Version. Retrieved February 23, 2021, from https://www.msdmanuals.com/professional/gastrointestinal-disorders/malabsorption-syndromes/short-bowel-syndrome

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