Short Bowel Syndrome
(Gut 2006;55:1-12. Gastroenterology 2003;124:1105-10 & 1111-34)
DEFINITION:
A malabsorptive state that often follows massive resection of the small intestine
The definition is a functional one: the extent or location of resection is independent of the degree of malabsorption
In general- patients develop symptoms when <200 cm of functional bowel remains
Intestinal failure: describes the state when GI function is inadequate to maintain the nutrient and hydration status of a person without intravenous or enteral supplementation
ETIOLOGIES:
Most common causes:
Adults: Crohn’s, Malignancy, Radiation enteritis, Vascular insufficiency, Trauma
Children: Crohn’s, Intestinal tumors, Radiation enteritis
Infants: Necrotizing enterocolitis, Intestinal atresia, Volvulus, Meconium ileus, Hirschsprung’s
PATHOPHYSIOLOGY:
Small bowel: Total length 390-690 cm (13-23 ft); 30 cm equals ˜1 ft
Duodenum (5%) 50 cm (1.5 ft); Jejunum (35%) 160-280 cm (4-9 ft); Ileum (60%) 240-420 cm (8-14 ft)
Colon 150-180 cm (5-6 ft)
Small bowel: absorbs about 10 L/day of ingested and secreted liquids
In general, patients develop symptoms when <200 cm of functional bowel remains
Majority of nutrient digestion/absorption is complete within first 100 cm of jejunum
Most will be able to maintain nutrient balance using oral feeds if 100 cm of jejunum is intact
Jejunal epithelium: relatively porous, allowing free and rapid flux of water and electrolytes – primary digestive and absorptive site
Characteristic long villi create a large absorptive area
Most carbohydrate, protein, water-soluble vitamins are absorbed in upper 200 cm of jejunum; Fat absorption occurs over a larger area
Ileum epithelium: site of significant reabsorption of fluid and electrolytes
Much less porous, hence potential for back diffusion of fluids and electrolytes is lower; shorter villi and reduced surface area
Adaptation: able to undergo massive adaptation via lengthening and function of villi – dependant on enteral nutrition!
Glucagon-like peptide II is major hormone involved in stimulating adaptation – stimulated primarily by fat
Ulcer disease initially due to hypergastrinemia: intestinal negative feedback for inhibiting gastrin secretion and reducing acid is interrupted
PUD and esophagitis are common
B12 intrinsic factor absorbed in ileum, therefore can result in B12 deficiency especially if >60 cm resected
Bile salts absorbed in ileum, therefore can result in bile acid malabsorption/decreased bile salts with malabsorption of fat-soluble vitamins
More than 100 cm of resected ileum results in disruption of the enterohepatic circulation (bile salt deficiency and fat malabsorption)
The delivery of unabsorbed bile acids to the colon can lead to secretory diarrhea (Cholerheic enteropathy); Also leads to hyperabsorption of oxalate, leading to hyperoxaluria and kidney stone formation
The jejunum secretes a large amount of fluid in response to any hypertonic feeds – this is reabsorbed primarily by the ileum
If a substantial portion of ileum (>100 cm) is resected, fluid and electrolyte loss will occur
This results in intolerance to large bolus feeds or feeds containing high concentrations of simple carbohydrates
Ileocecal valve: major barrier to reflux of colonic material from the colon to small intestine; regulator of ileal contents exiting to colon
Resection is associated with bacterial overgrowth-a major feature of short bowel syndrome
Colon is important too:
The presence of a colon is clearly a benefit in a patient with short bowel syndrome because of its ability to absorb water, electrolytes, short chain fatty acids
Colonic brake: signals small bowel to slow down; If no colon, no colonic break
Those without a colon and <100 cm of jejunum are likely to require life-long TPN
CLINICAL MANIFESTATIONS/PHYSICAL EXAM:
Symptoms associated with bowel resection are highly dependant upon the physiology of the remaining small bowel
See Pathophysiology above
Diarrhea: a major cause is the osmotic load generated by malabsorbed carbohydrates; especially true with simple carbohydratesRelated posts:
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