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Constipation in the Elderly: Causes

Why do old people become constipated? Generally for the same reasons that young people become constipated. Certainly they do not become constipated as a simple consequence of aging. There is not a shred of evidence that bowel function declines with advancing age. Although it is true that the incidence of colonic diverticula increases with age, these changes do not in themselves alter bowel function and do not correlate with constipation.

The factors which may lead to constipation are listed in Table 1 in rough order of their importance in the geriatric population. Obviously, several factors may be at work in a single patient.

  TABLE 1 Etiologic Factors in Constipation
1. Insufficient dietary fiber
2. Inactivity/immobility
3. ‘Gut reaction’ to stress: anxiety (irritable colon syndrome) or depression
4. Drugs
5. Inadequate fluid intake
6. Laxative abuse
7. Poor muscle power (diaphragm, abdominal wall)
8. Impaired mental state (dementia, confusional states)
9. Anal disease (fistula, fissure, stricture, prolapsing or thrombosed hemorrhoids)
10. Neurological disease (eg. multiple sclerosis, paraplegia, quadraplegia, spinocerebellar degeneration)
11. Others
— carcinoma of colon or rectum
— hypothyroidism
— diverticulitis
— stricture occurring as a complication of diverticulitis or ischemic colitis
— hypercalcemia
— hypokalemia
— carcinoma of pancreas or stomach

Dietary fiber plays a major role in the maintenance of normal bowel function. Fiber is “that part of plant material . . . which is resistant to digestion by the secretions of the . . . gastrointestinal tract”. It originates in plant cell walls. Peeling and boiling reduce fiber. Its usual effects are to increase stool weight, soften stools, decrease intestinal transit time and increase flatus. However, in individuals with reduced transit time added fiber increases transit time and reduces stool frequency, i.e. it normalizes colon motility. Fiber’s main laxative action is through absorption of water. Through augmenting free fatty acid production by intestinal bacteria, fiber may also exert an osmotic laxative effect. Increasing the fiber content in the diet of geriatric unit patients has been shown to reduce the need for laxatives. Bran is acknowledged to be without equal as a dietary source of fiber. Numerous studies have demonstrated its effectiveness in the management of chronic constipation.

Constipation

Inactivity impairs bowel function for reasons which are not clear. Brockelhurst and Khan found that debilitated geriatric long-stay patients had markedly greater intestinal transit time than active old people. The delay in transit time occurs exclusively in the large bowel.

The elderly face not only many of the life stresses encountered by the young but also a number which are specifically associated with aging, including retirement, death of friends, death of spouse, loss of income and deteriorating health. The toll which these crises exact may be reflected in impaired bowel function.

Drug-induced or aggravated constipation deserves special mention as it is often overlooked. Table 2 lists the main culprits.

  TABLE 2 Drugs Causing Constipation
1. Narcotic analgesics
2. Antacids containing aluminum hydroxide (eg. Amphogel) or calcium carbonate (eg. Turns)
3. Anticholinergics — eg. Bentylol (dicyclomine HCI), Buscopan (hyoscine butylbromide), Donnatal (belladonna alkaloids — phenobarbital), Pro-Banthine (probantheline bromide)
4. Narcotic-containing cough preparations
5. Iron preparations
6. Phenothiazines
7. Tricyclic antidepressants
8. Anti-Parkinsonian agents with anti-cholinergic properties, eg. Cogentin (benztropine mesylate), Artane (trihexphenidyl HCI)
9. Any drug resulting in oversedation and hence neglect of call to stool
10. Diuretics if they produce dehydration and/or hypokalemia

Several of the drugs listed (for example, narcotic analgesics and cough preparations) are frequently prescribed for individuals whose risk of developing constipation is already high due to a reduced level of activity.

A fluid intake level sufficient to maintain an adequate state of hydration is necessary to normal bowel function. Many elderly, particularly those who are debilitated, may be in a state of chronic dehydration because they lack the energy or the ability to obtain and drink fluids without encouragement or assistance. These individuals will benefit from increased fluids. However, raising fluid intake in those whose hydration is adequate, will not soften stools. The extra fluid will simply be absorbed from the gut and excreted by the kidneys.

Constipation

It has long been supposed that chronic laxative use somehow impairs subsequent bowel function. Some evidence is available to support that notion. Smith reported pathology findings in the colon of a female patient who underwent colectomy after 40 years of frequent laxative use. The number of myenteric neurons was decreased and the remaining neurons and axons showed distinct abnormalities. A mouse population given senna orally for four months showed axonal fragmentation and dendritic swelling in the myenteric plexus.

Constipation in mentally impaired patients is due at least in part to lack of rectal awareness. They do not initiate defecation even when the rectum is full.

Painful anal conditions may lead patients to inhibit defecation as a way of avoiding the anticipated discomfort.

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