[The physiology of intestinal pouches]

To summarize, J-shaped and W-shaped ileal pouches serve as adequate neorectal 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, which have efferent limbs positioned between the pouch and the anal canal, sometimes leads to outflow obstruction and incomplete evacuation. There is little doubt that neorectums made of ileum can allow patients to have entirely "normal" patterns of fecal continence. Nonetheless, with pouch distension, large-amplitude, propulsive pouch contractions occur. These large pressure waves bring on the urge to defecate. They stress the anal sphincters more acutely than either the infrequent, small-amplitude, nonpropulsive contractions or clustered contractions of the healthy rectum. Nonetheless, patients learn to recognize the different signals heralding the impending need for evacuation from the ileal pouch and deal with them. Jejunal pouches, because of their greater distensibility and larger capacity, and the greater frequency of interdigestive migrating myoelectric complexes (MMCs) occurring in them, hold the promise of being a better rectal substitute than ileal pouches. 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 substitutes after gastrectomy provide a better reservoir for ingested food than straight jejunal segments. The main drawback of the pouches is their inability 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 these pouches at the same rate, in contrast to the slower emptying rate of solids from the healthy stomach. This likely leads to maldigestion of solids, perhaps contributing to the weight loss often found after gastrectomy.