Small bowel and nutrition

See separate topic under 'small bowel' - which is more focused on the surgical aspect of things

Physiology

• Majority of fluid and electrolytes are reabsorbed in the ileum
  • Only site of absorption of B12 and bile salts
• >90% of water and salt in colon is reabsorbed

Effects of bowel resection

• Up to 50% of small bowel can removed or bypassed.
  • Resection of proximal jejunum - no significant alteration in fluid and electrolyte absorption, as ileum and colon can pick up the slack entirely
  • Resection of ileum
    • Clinically generally leads to diarrhoea and deficiencies
      • B12 malabsorption - macrocytic anaemia and peripheral neuropathy
      • Bile salt malabsorption - steatorrhoea, oxalate renal stones, gallstones
        • Loss of fat-soluble vitamins ADEK - poor wound healing, impaired calcium homeostasis, coagulopathy
    • Accelerated intestinal transit which leads to gradual undernutrition
    • Depletion of bile salt pool cannot be replaced by synthesis in absence of ileum
    • Loss of bile salts into colon also affects colonic mucosa, causing an additional reduction in level of absorptive capacity
    • Loss of 100cm of ileum causes steatorrhoea, which may necessitate the administration of oral cholestyramine. Sometimes restriction of oral fat intake will be necessary. Regular B12 IV will be necessary.
    • May need parenteral nutrition if <50cm small bowel remains
    • Need a high carbohydrate/low oxalate diet
    • May adapt over time to rely on artificial nutrition less
  • Resection of >2m of small bowel and colon +/- end jejunostomy
    • Short gut syndrome - very challenging
    • See separate topic on 'short gut syndrome' under 'small bowel'
    • Adaptation does not occur
    • Net absorbers
      • >100cm of residual jejunum and they absorb more water and sodium from diet than passes through the stoma
      • Can usually be managed without supplemental IV fluids
    • Net secretors
      • <100cm of residual jejunum and lose more water and sodium from their stoma than they take by mouth
      • Require supplemental IV fluids
      • Daily jej output may be >4 litres
      • Sodium content of jej losses will be about 90mmol/L. If hypotonic solutions e.g. water are drunk, sodium will be lost across bowel lumen through diffusion
      • Treatment - restrict hypotonic fluids to 1L per day, take glucose and saline replacement solutions
    • Complications of short bowel syndrome:
      • Peptic ulceration (related to gastric hypersecretion)
      • Cholelithiasis
      • Hyperoxaluria (increased absorption of oxalate in colon predisposes to kidney stones)
      • Syndrome of slurred speech, ataxia, altered affect - due to fermentation of malabsorbed carbohydrates in colon - treat with low carbohydrate diet
• Metabolic consequences arise with <150cm of small bowel - 'short gut syndrome'