Decrease in the anorectal pressure gradient after low anterior resection of the rectum

PURPOSE: Changes in anorectal function after low anterior resection of the rectum (LAR) often lead to symptoms of urgency and frequency of defecation, the anterior resection syndrome. It has been reported that preservation of part of the rectum improves clinical results, but why this should be remains unclear. METHODS: We have carried out continuous ambulatory manometric studies in two groups of patients: 11 patients, a median of 11 (range, 5-96) months after LAR, in whom the median anastomotic level above the anal high-pressure zone was 0 (range, 0-2) cm; 9 patients, a median of 6 (range, 3-12) months after sigmoid colectomy, in whom the rectum remained in situ and who acted as controls. RESULTS: Comparing the LAR group with controls, resting anal pressures were lower, median 68 (range 27-102) cm H2O vs. 95 (45-116) cm H2O (P<0.05), and neorectal pressures were higher, 25 (0-48) cm H2O vs. 10 (0-10) cm H2O (P<0.01). Thus the anorectal pressure gradients were less, 34 (0-74) cm H2O vs. 81 (35-113) cm H2O (P<0.01). Slow-wave activity in the anal sphincter was present in six patients (55 percent) after coloanal anastomosis and eight patients (89 percent) after sigmoid colectomy. Sampling episodes were seen in only two patients (18 percent) after coloanal anastomosis and five patients (56 percent) after sigmoid colectomy. When clinical endpoints were compared (LAR vs. controls), bowel frequency in 24 hours was higher, 5 (3-8) vs. 2 (1-3) (P<0.01); fecal leakage was more common, affecting seven patients (64 percent) vs. one patient (11 percent) (P<0.05), and urgency of defecation was also more common. CONCLUSIONS: The inferior clinical results observed after LAR compared with the results after sigmoid colectomy are thus in part because of higher neorectal pressure acting on a weakened sphincter mechanism. These observations lend support to the idea that neorectal capacity should be increased in patients who undergo low anterior resection.