The physiology of intestinal pouches

To summarize, J-shaped and W-shaped ileal pouches serve as adequate neorect al reservoirs after proctocolectomy. These pouches anastomosed directly to the anal canal are as distensible and capacious and as readily evacuated as the rectum in health. However, the use of S- or H-shaped ileal pouches, wh ich have efferent limbs positioned between the pouch and the anal canal, so metimes leads to outflow obstruction and incomplete evacuation. There is li ttle doubt that neorectums made of ileum can allow patients to have entirel y "normal" patterns of fecal continence. Nonetheless, with pouch distension , large-amplitude, propulsive pouch contractions occur. These large pressur e waves bring on the urge to defecate. They stress the anal sphincters more acutely than either the infrequent, small-amplitude, nonpropulsive contrac tions or clustered contractions of the healthy rectum. Nonetheless, patient s learn to recognize the different signals heralding the impending need for evacuation from the ileal pouch and deal with them. Jejunal pouches, becau se of their greater distensibility and larger capacity, and the greater fre quency of interdigestive migrating myoelectric complexes (MMCs) occurring i n them, hold the promise of being a better rectal substitute than ileal pou ches. They are more difficult to construct, however. Colonic pouches, when anastomosed to the anal canal after rectal resection, also act as adequate fecal reservoirs. Their main drawback is the inability of some patients to empty them. Small (5 cm) colonic pouches seem to empty better than larger ( 10-15 cm) ones. Jejunal pouches and colonic segments used as gastric substi tutes after gastrectomy provide a better reservoir for ingested food than s traight jejunal segments. The main drawback of the pouches is their inabili ty to triturate the solid content of a meal and to regulate the rate of its emptying into the small intestine. Liquids and solids likely empty from th ese pouches at the same rate, in contrast to the slower emptying rate of so lids from the healthy stomach. This likely leads to maldigestion of solids, perhaps contributing to the weight loss often found after gastrectomy.