Motor function of the ileal J pouch and its relation to clinical outcome after ileal pouch‐anal anastomosis

Abstract The motor function of the ileal J pouch after ileal pouch‐anal anastomosis has a key role in the clinical outcome. The pouch forms a neorectum that aids in the maintenance of reasonable continence. The maximum capacity of the pouch (mean, 320 ml) is similar to that of the healthy rectum (330 ml). The pouch accommodates to distension, keeping intrapouch pressure low as the pouch gradually fills with stool. The change in pouch volume with each change in pressure (15 ml/mm Hg) approximates that of the healthy rectum (19 ml/mm Hg). When a threshold volume of about 150 ml is reached, large‐amplitude (>25 mm Hg), prolonged (40–60 sec), propulsive waves appear in the pouch. They initiate the call to stool. With continuing distention of the pouch to its functional capacity, which is about 200 ml, reflux of stool into the distal ileum begins, the large pressure waves become more frequent, and the urge for defecation more intense. Defecation is voluntary, spontaneous, and rapid (11 ml/sec), with the pouch and distal ileum emptying concurrently. About 60% of the pouch content, a volume of about 100 ml of stool, is discharged with each bowel movement. The greater the threshold volume and the more complete the evacuation, the fewer the bowel movements per day. After evacuation, the large pressure waves subside, and the next cycle of pouch filling and emptying begins.