What is short bowel syndrome?

Short Bowel Syndrome Definition

Short bowel syndrome (SBS) is a devastating clinical pathological syndrome resulting from the loss of intestinal length due to disease or surgical resection, generally defined as a residual small intestinal length of 200 cm or less. 1

Definition and Diagnostic Criteria

• SBS occurs when, after surgery or congenitally, a patient is left with insufficient functional small intestine, leading to malabsorption of nutrients, fluids, and electrolytes 1
• While 200 cm is the generally accepted threshold, some reports suggest that a residual length of 150 cm or less may be more appropriate for diagnosis 1
• The measurement of bowel length should be taken from the duodenojejunal flexure to the ileocecal junction, the site of any small bowel-colon anastomosis, or to the end-ostomy 1
• Normal human small intestinal length varies from approximately 275 cm to 850 cm, and tends to be shorter in women 1

Anatomical Classification

SBS patients can be classified into three distinct anatomical groups:

• Group 1: End-jejunostomy - patients with jejunoileal resection, colectomy, and formation of a stoma (most severe phenotype) 1
• Group 2: Jejunocolonic anastomosis - patients with jejunoileal resection and jejunocolic anastomosis (partial colon) 1
• Group 3: Jejuno-ileo-colic anastomosis - patients with jejunal resection but intact ileum and colon (most favorable phenotype) 1

Clinical Manifestations

• General consequences include diarrhea, dehydration, electrolyte abnormalities, and weight loss due to loss of digestive and absorptive surface area 1, 2
• Specific consequences relate to the regions of gastrointestinal tract missing:
  • Terminal ileum loss: vitamin B12 deficiency, bile acid-induced diarrhea 1
  • Colon loss: increased fluid and electrolyte losses 1
• Patients at greatest nutritional risk generally have:
  • Duodenostomy or jejunoileal anastomosis with ≤35 cm of residual small intestine 1
  • Jejunocolic or ileocolic anastomosis with ≤60 cm of residual small intestine 1
  • End jejunostomy with ≤115 cm of residual small intestine 1

Relationship to Intestinal Failure

• While SBS and intestinal failure (IF) are often used interchangeably, they represent distinct concepts 1
• IF is defined as the reduction of gut function below the minimum necessary for absorption of macronutrients or water and electrolytes, requiring intravenous supplementation 1
• SBS is the most common cause of IF, but IF can also result from other disorders like chronic intestinal pseudo-obstruction 1
• IF severity is classified as:
  • Severe: requiring parenteral nutrition
  • Moderate: requiring enteral nutrition
  • Mild: requiring oral nutritional supplements 1

Prognostic Factors

• The remaining anatomy and length of bowel after intestinal resection have important prognostic implications 3
• Presence of the ileocecal valve and functional colon significantly improves prognosis 1, 4
• Patients with jejunum-colon anatomy may need parenteral nutrition if less than 50 cm small intestine remains 1
• Patients with jejunostomy may need:
  • Parenteral saline if less than 100 cm of jejunum remains
  • Parenteral nutrition and saline if less than 75 cm remains 1
• The probability of weaning from parenteral nutrition becomes less than 10% if not achieved within the first 2 years following the last bowel resection 5

Clinical Complications

• Fluid and electrolyte imbalances, particularly hypomagnesemia 1, 4
• Malnutrition and specific nutrient deficiencies (vitamins, minerals, trace elements) 2
• D-lactic acidosis from bacterial fermentation of unabsorbed carbohydrates 4
• Renal oxalate stones (25% risk in patients with preserved colon) 4
• Gallstone formation (45% in short bowel patients) 4
• Small intestinal bacterial overgrowth, especially when the ileocecal valve has been resected 4, 2

SBS represents a spectrum of disease severity requiring individualized management by an experienced multidisciplinary team, with treatment approaches varying based on the remaining bowel anatomy, length, and function 3.