The Pediatric Pouch in Inflammatory Bowel Disease

A Primer for the Gastroenterologist

Ghassan T Wahbeh; David L Suskind; Scott D Lee; John T Waldhausen; Karen F Murray

Disclosures

Expert Rev Gastroenterol Hepatol. 2013;7(3):215-223. 

In This Article

Anticipated Changes After Colectomy

The main colonic functions are absorption, storage, evacuation and maintaining homeostasis with its massive microbiome. Water, sodium, chloride, calcium, oxalate and vitamin K are absorbed in the colon. A key challenge after colectomy is dehydration and electrolyte loss. However, by the time bowel continuity is restored, commonly 3 months after pouch creation, the small bowel will usually have compensated for such losses. Salvaged carbohydrates fermented by the colonic microbiota to short chain fatty acids (SCFA) are reabsorbed through the colon. While healthy, the SCFA caloric contribution to the body is negligible. However, SCFA may modulate mucosal inflammation, lending basis to their use in pouchitis management. The ileocecal valve prevents reflux of the colonic contents into the ileum and regulates colonic filling. The implication of the absence of such a barrier in a pouch is unclear. Although the rectum has the largest capacity within the colon, in healthy individuals it is usually empty until shortly before defecation. Stools can be stored in any part of the colon, including the ascending colon.[8] The smaller volume that a pouch offers has obvious restrictions, leading to the frequent bowel movements a child is expected to have, even with a healthy pouch. Intermittent colonic contraction waves further prepulse the colonic contents distally. When the rectum is filled and its mechanoreceptors are stimulated, a reflex arc through the sacral spinal nerves mediates the defecation sequence that includes urge sensation, internal anal sphincter relaxation (through the rectoanal inhibitory reflex) and, when appropriate, a voluntary relaxation of the external anal sphincter. The angle between the rectum and anal canal is reshaped by posture (sitting or squatting) and pelvic floor muscle relaxation, allowing less resistance to outflow. The increased intrapelvic pressure (Valsalva or straining) and colonic peristalsis result in stool and air evacuation. Since the pouch innervation and anatomy within the pelvis are different from the native colon, this may well affect the evacuation function for many patients.

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