Editing Short bowel syndrome (section)

== '''Pathophysiology''' ==

* Intestinal failure - inadequate bowel function to maintain nutrition and hydration, including macro- and micro-nutrients, electrolytes and fluid volumes
* Phases:
** Acute hypersecretory phase - 3-4 weeks
*** Malabsorptive and osmotic (and sometimes bile salt) diarrhoea due to lack of absorption of fluid and electrolytes and macronutrients
** Adaptation - 1-2 years
*** Requires enteral nutrition
*** This is where the structural and functional changes below occur
** Late
*** Plateaued adaptations
* Adaptive hyperplasia - the bowel's adaptive capacity after resection
** Stimulated by nutrients within the intestinal lumen
** Structural adaptation
*** Dilation and elongation of the remnant bowel via muscle hyperplasia
*** Villus lengthening and increase in microvilli
*** Increase in enterocyte number
*** Crypt cell proliferation
*** Angiogenesis for improved perfusion
*** Slowed transit time
** Functional 
*** Increased expression of transporter proteins and exchangers
*** Increased production digestive enzymes
*** Improved digestion from enterocytes
* Requirement for parenteral nutrition is influenced by length, location and health of the remaining intestine, but commonly:
** Measure from DJ flexure. 
** >180cm: no PN
** 60-180cm: PN for less than 1 year
** <50-60cm: permanent PN
** Interestingly, UTD doesn't list any such guidelines, merely that it is highly dependent on function of the remaining bowel
* Bowel anatomy factors:
** Jejuno-colic anastomosis - most common anatomy - prognosis depends on length of jejunum remaining
** Jejuno-ileocolic anastomosis (retention of some ileum and ICV - best prognosis
** End-jejunostomy - worst prognosis
** Proximal bowel resection is tolerated better than distal - the ileum can adapt and restore absorptive capacity better than the jejunum
** Presence of at least half the colon is functionally equivalent to having an extra 50cm of small bowel