Short Bowel Syndrome (SBS)

Definition

• Harrison's Principles of Internal Medicine 22E, p. 2591
• Sleisenger and Fordtran's Gastrointestinal and Liver Disease, p. 1720

Etiology

Adults

Pediatric/Congenital

90% of infants now survive the extensive resections required for these conditions, but require long-term follow-up.

• Sabiston Textbook of Surgery, p. 2686
• Schwartz's Principles of Surgery 11th Ed., p. 1282

Incidence & Prevalence

• The incidence of severe SBS requiring long-term PN is estimated at 2-4 cases per million persons per year (multinational European data).
• An estimated 10,000-20,000 patients in the USA follow a home PN regimen for SBS.
• ~50-70% of patients who initially require PN can eventually be weaned from it.
• The incidence of SBS from Crohn's disease is likely decreasing due to biological therapies and bowel-sparing surgical techniques (strictureplasty).
• Sleisenger and Fordtran's, p. 1720

Anatomy and Physiology of Absorption (Why SBS Causes Problems)

• Proximal 100-150 cm (duodenum/jejunum): Absorbs most macronutrients - carbohydrate, fat, nitrogen, and most minerals (calcium, iron, magnesium, folate)
• Jejunum: Site of absorption of most macronutrients and many minerals; contains the ileal brake (GLP-1 mediated) which suppresses gastric secretion and slows emptying
• Terminal ileum: Essential and site-specific for:
  • Bile salt reabsorption (enterohepatic circulation)
  • Vitamin B12 absorption (via intrinsic factor receptors)
  • Fat-soluble vitamins (A, D, E, K)
  • Carbohydrates, proteins, fluids, electrolytes
  • Production of GLP-1 and GLP-2 from L-cells
• Colon: Absorbs water and electrolytes; metabolizes malabsorbed carbohydrates into short-chain fatty acids (SCFAs) via bacterial fermentation - contributing several hundred extra kcal/day

• Sabiston Textbook of Surgery
• Sleisenger and Fordtran's, p. 1722

Pathophysiology

1. Loss of Absorptive Surface Area

• Length of remnant intestine
• Site of resection (ileal > jejunal in severity)
• Presence/absence of the colon
• Ileocecal valve status
• Health of residual bowel (diseased vs. normal)

2. Gastric Acid Hypersecretion

• Inhibits digestive enzymes (which function optimally at alkaline pH)
• Causes diarrhea and mucosal damage
• Overwhelms the buffering capacity of the residual intestine

3. Bile Salt Wasting

• Resection of <100 cm of ileum: Bile salts reach the colon and cause secretory diarrhea (cholerheic diarrhea). Hepatic synthesis can compensate.
• Resection of >100 cm of ileum: Bile salt malabsorption so severe that the liver cannot compensate → fat malabsorption (steatorrhea) due to bile salt insufficiency

4. Loss of Ileal Brake

5. Rapid Transit

6. Bacterial Overgrowth

• Deconjugates bile salts
• Competes for nutrients
• Causes mucosal inflammation and diarrhea

7. Specific Nutrient Deficiencies

• Harrison's Principles, p. 2591
• Schwartz's Principles, p. 1282

Clinical Phases

Phase 1: Early Postoperative (0-3 months)

• Massive diarrhea (may be several liters/day, especially with jejunostomy)
• Severe dehydration
• Electrolyte disturbances (Na+, K+, Mg2+, HCO3- loss)
• Gastric acid hypersecretion peaks
• TPN dependence

Phase 2: Intestinal Adaptation (up to 1-2 years; improvements possible 3-5 years)

• Gradual reduction in stool volume and frequency
• Increasing capacity for enteral nutrition
• Adaptive hyperplasia developing in residual bowel

Phase 3: Stabilization / Chronic Phase

• Ongoing nutritional monitoring required
• Some patients achieve enteral autonomy; others remain PN-dependent
• Long-term complications become the focus of management

Intestinal Adaptation

• Mucosal hyperplasia begins within 48 hours of resection
• Increased crypt cell proliferation → epithelial hyperplasia
• Villous hypertrophy increases surface area
• Bowel dilation and elongation

• GLP-2 (from L-cells in terminal ileum/colon) - most potent known stimulant; mediates trophic effects on villous heights and crypt depths
• EGF (epidermal growth factor)
• IGF-1 (insulin-like growth factor-1)
• TGF-α (transforming growth factor-alpha)
• IL-11
• VEGF, CCK, gastrin, insulin, neurotensin, PDGF-α
• Polyamine synthesis in crypt cells
• Luminal nutrients and biliary/pancreatic secretions (essential - adaptation fails with PN-only feeding)

• Elemental/enteral diet
• Presence of food in the lumen (early oral feeding)
• Presence of bile and pancreatic secretions
• Colonic flora changes (increased Lactobacillus species)

• Sleisenger and Fordtran's, p. 2108
• Goldman-Cecil Medicine International Edition

Long-Term Complications

1. Gallstones

2. TPN-associated Liver Disease

• Cholestasis, hepatic steatosis → cirrhosis
• Significant source of morbidity; can require combined liver + small bowel transplantation

3. Calcium Oxalate Kidney Stones

• Occurs in patients with an intact colon
• Mechanism: Fat malabsorption → fatty acids bind calcium in the lumen (saponification) → oxalate not bound → free oxalate absorbed in colon → hyperoxaluria → calcium oxalate stones

4. Osteoporosis

• Fat malabsorption → vitamin D deficiency (very difficult to treat even with high-dose oral vitamin D)
• Calcium malabsorption
• Monitor with DEXA scans

5. D-Lactic Acidosis

• Colonic bacteria ferment malabsorbed carbohydrates to D-lactate (not metabolized by mammalian lactate dehydrogenase)
• Presents with: encephalopathy, ataxia, slurred speech, high anion gap metabolic acidosis

6. Bacterial Overgrowth

• Multiple surgeries → adhesions → abnormal motility and strictures → recurrent SIBO

7. TPN-specific complications

• Catheter-related bloodstream infections (CRBSI)
• Central venous thrombosis
• Renal failure
• 5-year survival on long-term TPN: 50-75%
• Harrison's Principles, p. 2591-2592
• Schwartz's Principles, p. 1282

Management

Immediate / Perioperative

1. Hemodynamic stabilization and aggressive fluid/electrolyte resuscitation
2. TPN initiation - almost universally required initially
3. High-dose IV H2 antagonists or PPIs - to suppress hypergastrinemia-driven acid hypersecretion
4. Measure losses - weigh patient, measure stoma/fecal outputs, urinary losses of water, Na+, K+ daily
5. Second-look laparotomy at 24-48 hours for extensive resections to assess anastomotic healing

Medical Management

Antidiarrheal / Antimotility Agents

• Loperamide: 2-8 mg PO up to 4 times daily (first-line)
• Diphenoxylate/atropine: 1-2 tablets PO up to 4 times daily
• Codeine: 15-60 mg PO up to 4 times daily
• Tincture of opium: 0.3-1 mL PO 4 times daily (severe cases)
• Liquid morphine 20 mg/mL: 1 mL PO 4 times daily (severe cases)

Acid Suppression (first 1-2 years post-resection)

• PPI: Omeprazole 40 mg daily, or lansoprazole 30 mg daily
• H2RA: IV initially, then oral

Antisecretory Therapy

• Octreotide: 100-250 mcg SC three times daily for high-volume outputs (>3 L/day); if effective, convert to long-acting monthly formulation
• Caution: Octreotide inhibits intestinal adaptation and impairs pancreatic enzyme secretion - so benefit may be offset

Oral Rehydration

• ORS with sodium concentration 75-90 mmol/L (absorbed best)
• High-salt, nutrient-dense diet in small frequent meals
• Patients with <100 cm jejunum and no colon often require IV fluids or PN to survive

Antibiotic Therapy for SIBO

• Rifaximin, metronidazole, or rotating antibiotics when SIBO is suspected

Bile Acid Resins

• Cholestyramine: Only for ileal resection <100 cm (cholerheic diarrhea); contraindicated if >100 cm resected (worsens fat malabsorption)

Vitamin and Micronutrient Supplementation

• High-potency daily multivitamin
• Vitamin B12: 500-1000 mcg IM or SC monthly (parenteral route mandatory with ileal resection)
• Magnesium: liquid preparation sipped throughout day in ORS (IV if severe)
• Fat-soluble vitamins, folic acid, iron, zinc
• Monitor copper, selenium, chromium in TPN-dependent patients
• Periodic DEXA scans, vitamin D levels, and calcium

Pharmacologic Enhancement of Bowel Adaptation

Teduglutide (GLP-2 analogue) - FDA Approved

• Mechanism: Enhances crypt cell proliferation and villus hyperplasia; increases nutrient, fluid, and electrolyte absorption; improves intestinal barrier function; reduces gastric secretions; improves intestinal blood flow
• Efficacy: Average 20% reduction in PN requirements; greater efficacy in patients without a residual colon (lower endogenous GLP-2 levels)
• Indication: PN/IV fluid-dependent adult patients with SBS

GLP-1 Agonists (e.g., Exenatide)

• GLP-1 delays gastric emptying and slows small bowel motility
• Showing promising results in reducing TPN need

Growth Hormone + Glutamine

• Combination with dietary adjustment has shown promise in reducing or eliminating TPN
• However, trials are short and patients often return to baseline undernourishment after stopping
• Current evidence is inconclusive; not routinely recommended

Nutritional/Dietary Therapy

Surgical Management (Non-Transplant)

Procedures to Slow Transit (mostly historical/rarely used)

• Reversed intestinal segment
• Recirculating loop
• Artificial intestinal valve
• Colon interposition
• Intestinal pacing
• Outcome: Poor efficacy, high risk of obstruction - largely abandoned

Intestinal Lengthening Procedures (for dilated residual bowel)

• Mesenteric vascular bed separated into two systems
• Dilated small intestine split longitudinally into two parallel segments, each with its own blood supply
• Ends anastomosed isoperistaltically
• Result: 50% decrease in diameter, 100% increase in length
• Technically demanding; risk of ischemia if blood supply compromised

• Dilated bowel stapled serially in a transverse V-shape on alternating sides
• Decreases width and increases length without separating mesenteric vasculature
• International registry of 111 patients: 47% achieved enteral autonomy at median 21 months
• Can be repeated if bowel re-dilates

FIGURE: Bowel-lengthening procedures. (A) Bianchi technique. (B) Serial transverse enteroplasty (STEP). Source: Sabiston Textbook of Surgery.

• Sabiston Textbook of Surgery, p. 2686

Restoration of Intestinal Continuity

• Among patients with stomas, restore continuity whenever possible to maximize absorptive surface

Intestinal Transplantation

1. Impending or overt liver failure (TPN-associated cholestasis/cirrhosis)
2. Thrombosis of major central veins (loss of venous access)
3. Frequent catheter-related sepsis (recurrent CRBSI)
4. Frequent episodes of severe dehydration

• Intestine-alone: 37%
• Intestine + liver + pancreas: 30%
• Intestine + liver: 24%

• Schwartz's Principles, p. 1282

Summary of Anatomic Outcomes and TPN Dependence

Key Points Summary

• SBS = malabsorption from <200 cm residual small bowel; intestinal failure = PN dependence, typically <100 cm without colon
• Most common adult cause: Crohn's disease; pediatric: NEC
• Severity determined by: length, site of resection (ileum > jejunum), colon presence, ileocecal valve, bowel health
• Ileal resection is uniquely devastating (B12, bile salts, GLP-2 loss)
• Colon salvages fluid and calories (SCFAs); its presence significantly changes management
• Intestinal adaptation takes 1-2 years (up to 5 years); requires luminal nutrients - early oral/enteral feeding is mandatory
• Citrulline >20 μmol/L predicts nutritional autonomy
• Teduglutide (GLP-2 analogue) is the only FDA-approved SBS-specific pharmacotherapy; averages 20% PN reduction
• Bowel-lengthening procedures (STEP/Bianchi) used for dilated bowel in pediatric patients
• Transplantation reserved for life-threatening TPN complications