Why do patients with faecal impaction have faecal incontinence.

To elucidate the phenomenon of faecal incontinence in impacted patients, manometric, radiological and other investigations were carried out in 55 elderly patients, who had impacted masses of faeces in the rectum and were incontinent of faeces and 36 elderly control subjects with no anorectal problems. Maximum basal pressure and the maximum squeeze pressure in impacted patients were not significantly different from elderly controls. Sphincter pressures were no different after disimpaction than they were with faecal masses in situ, suggesting that leakage and soiling were not caused by stretching of the anal ring or prolonged reflex inhibition of anal tone by the faecal mass. The anorectal angle was more obtuse in impacted patients than in elderly controls though there was no greater degree of perineal descent. Anal and perianal sensation was impaired in impacted patients compared with controls. Rectal sensation was also impaired in the impacted patients in that the volume in a rectal balloon that could be perceived by the subject and the volume that gave rise to a desire to defecate were much higher in impacted patients than in controls. The rectal volume required to cause anal relaxation was lower in impacted patients compared with controls though there was no reduction in the volume at which anal relaxation failed to recover its resting tone. Rectal distension elicited external sphincter contractions in 53% impacted patients compared with 80% of controls. In conclusion, faecal soiling in patients with faecal impaction is probably related to the combination of an obtuse anorectal angle and the low anal pressures, normally found in the elderly and to impaired anorectal sensation which prevents conscious contraction of the external sphincter when the internal sphincter is relaxed.

Effect of aging on anorectal function.

Measurements of anorectal function were conducted on 37 elderly (66-87 years) and 48 young (19-55 years) normal subjects. Elderly subjects had decreased anal pressures compared with younger subjects, required lower rectal volumes to inhibit anal sphincter tone and had increased rectal pressures upon balloon distension. The rectal volume required to cause the desire to defecate and the maximum tolerated volume were lower in the elderly, but the corresponding rectal pressures were similar, indicating the sensations were mediated by tension, or pressure receptors. Rectal contractions were generated at similar degrees of rectal distension. A lower proportion of elderly, compared with young subjects could defecate a sphere 18 mm in diameter within 20 seconds. The degree of perineal descent was greater in the elderly female subjects compared with the young women, although there was no difference in this measurement between men. The anorectal angle was similar in young and old. The changes in anorectal function in the elderly would tend to make them more susceptible to faecal incontinence.

Anorectal function in elderly patients with fecal impaction.

Manometric and other investigations were carried out in 55 elderly patients who had impacted masses of feces in the rectum upon admission to hospital and in 36 elderly age- and sex-matched control subjects. Maximum basal and maximum squeeze sphincter pressures in the patients were similar to those in the elderly controls. Most elderly patients in the impacted group and all control subjects were able to pass a 50-ml balloon from the rectum, although a lower proportion of patients, admitted with impaction, could expel a small solid sphere. In patients the rectum had to be distended with larger volumes than in controls before the presence of the rectal balloon, pain, and the desire to defecate were perceived and before rectal contractions were generated. Rectal pressures, recorded during rectal distention, were lower in the impacted group than in the control group. Finally, anal and perianal sensation was impaired in patients with fecal impaction. These findings are similar to those described in patients with low spinal cord injuries.