Constipation

A decrease in stool frequency.

Constipation has different meanings to different people, making a precise definition elusive. The medical community usually defines constipation as a decrease in stool frequency; however, patients may also consider constipation as difficult passage of feces, hardness of stool, or a feeling of incomplete evacuation.

Constipation is more common in elderly persons--who report more straining and sensation of anal blockage--than in middle-aged persons. Constipation is the most common gastrointestinal complaint in the elderly, with up to 60% of elderly outpatients reporting laxative use. The overall prevalence of self-reported constipation is 24 to 37%, with women reporting more constipation than men. In the institutionalized elderly, up to 50% self-report constipation and up to 74% use laxatives daily.

Etiology

Age-related changes in anorectal physiology that predispose the elderly to constipation include increased rectal compliance and impaired rectal sensation (such that larger rectal volumes are needed to elicit the desire to defecate). Elderly persons also have reduced resting anal sphincter pressure and decreased maximal sphincter pressure, which predispose to fecal incontinence. Delayed colonic transit, an age-related change occurring predominantly in the rectosigmoid region, plays a small role.

Various medical and surgical conditions can cause or worsen constipation (see Table 110-1). Medications (see Table 110-2), low dietary fiber, and reduced caloric intake are common causes. Functional impairment from immobility, muscular weakness, and neuromuscular disorders make recognition of the need to defecate difficult. Altered mental status or depression may also contribute to constipation. Several factors contributing to constipation can often be identified in a single patient.

Symptoms, Signs, and Complications

Constipation in the elderly is typically divided into two major categories: functional megarectum, which manifests as an enlarged rectum and fecal impaction, and rectosigmoid outlet delay, which manifests as straining and passage of small hard stools. Pelvic floor dysfunction also results in outlet delay. This condition occurs predominantly in elderly women because of pelvic floor laxity and failure of the anorectal angle to open.

About 50% of elderly persons describe their constipation as infrequent defecation, 20% as excessive straining or incomplete evacuation, and 30% as both. Constipation can lead to abdominal discomfort, loss of appetite, and nausea. The belief that constipation can cause mild fever is unproven.

The major complication of constipation in the elderly is fecal impaction, which can result in intestinal obstruction, colonic ulceration (also called stercoraceous ulceration), overflow incontinence (leakage of stool around obstructing feces), or paradoxical diarrhea. Fecal impaction is most likely in patients with limited mobility or mental capacity who present with an alteration in bowel habit (eg, reduced frequency, new-onset diarrhea, incontinence). Urinary retention and urinary tract infections also occur with fecal impaction. Excessive straining may have deleterious effects on the cerebral, coronary, and peripheral arterial circulation, resulting in syncope, cardiac ischemia, and transient ischemic attacks. Also, excessive straining can result in hemorrhoids, anal fissures, and rectal prolapse with consequent anal pain and bleeding.

Idiopathic megacolon occurs rarely in elderly patients with chronic constipation. Colonic dilatation can be quite marked and predisposes patients to colonic volvulus.

Diagnosis

When evaluating a patient with constipation, the first priority is understanding the patient's complaint. Attention should be directed to the patient's beliefs about bowel habits and to psychologic status; misperceptions about normal bowel movement frequency can be identified and corrected.

Appropriate screening for depression and anxiety may uncover previously unrecognized and treatable conditions. Reviewing the patient's history of underlying medical conditions or medications (see Tables 110-1 and 110-2) may uncover potential contributing factors.

A physical examination is performed primarily to detect evidence of metabolic, muscular, or neurologic disease. All patients should undergo a rectal examination to evaluate for the presence of perineal lesions, to characterize the stool (ie, small, hard stools, soft stools), and to exclude a low rectal or anal mass. The presence of an empty rectal vault does not exclude the possibility of a higher stool impaction.

Laboratory studies can exclude suspected underlying metabolic conditions, especially hypothyroidism. An abdominal x-ray shows the amount and distribution of stool in the colon; the presence of air fluid levels should prompt surgical consultation.

Colonoscopy or barium enema should be performed in a patient with a recent change in bowel habit to rule out underlying structural lesions (eg, malignancy, stricture). The presence of anemia or heme-positive stool also necessitates an assessment that includes colonoscopy.

In patients with intractable symptoms, assessment of colonic transit and anorectal function may be helpful. Colonic transit can be measured by using radiopaque markers. A capsule containing 24 markers is given at day 0. The patient must avoid laxatives and enemas for the duration of the test. On day 5, a plain abdominal x-ray is taken. If more than five markers remain, colonic transit is delayed. More complex versions of this test (to quantitate segmental colonic transit) are probably unnecessary because drugs to correct these abnormalities are unavailable.

Techniques used to assess anorectal function include defecating proctography and anorectal manometry. Defecating proctography measures defecation dynamics using barium instilled into the rectum. Abnormalities that can be identified include rectoceles, intussusception, prolapse, poorly relaxing puborectal muscle, and excessive perineal descent. Anorectal manometry measures rectal sensation, anal pressures, and expulsion dynamics.

Treatment

Constipation can be treated in most elderly persons with dietary and behavioral changes and judicious use of laxatives and enemas. Agents used to treat constipation are listed in Table 110-3.

Dietary approaches begin with adequate hydration, a cornerstone to treating constipation, especially in elderly persons who use diuretics. Food with high residual fiber (eg, bran and other whole grains, vegetables, nuts) is often beneficial and obviates the need for supplemental fiber. Although some people experience bloating and excessive gas initially, these symptoms usually resolve with continued use. When dietary approaches alone do not provide enough fiber (usually 20 g/day are needed), fiber supplementation (eg, methylcellulose, psyllium) is helpful. Because many of these products are high in sugar, they must be selected carefully.

In patients with idiopathic megacolon or other colonic dilatation (eg, bowel obstruction, megarectum), fiber supplementation is not helpful and should be avoided. These patients require a fiber-restricted diet with a regular schedule of laxatives or enemas to minimize fecal retention and impaction. A stool impaction, if present, should be removed before initiating fiber therapy.

Other foods (eg, prunes, melons, other foods with complex carbohydrates) can also help normalize bowel movements.

Behavioral changes include exercise, which strongly stimulates defecation and helps strengthen the abdominal muscles that aid defecation. Patients with constipation should attempt to move their bowels in the early morning, especially after breakfast, when colonic motor activity is highest.

Laxatives are usually recommended if dietary and behavioral changes cannot be achieved or are ineffective. Laxatives should be chosen according to the cause of the constipation. For most persons with chronic constipation, osmotic laxatives are effective and present the lowest risk. Lactulose and sorbitol (from 7.5 to 30 mL daily) are effective and safe. The dose is adjusted to produce a bowel movement daily or every other day. Osmotic laxatives containing magnesium are suitable only for short-term use and for patients without renal insufficiency.

For acute constipation or constipation caused by medications (especially opioids), stimulant laxatives (including senna and cascara) are generally best. They can be taken orally or rectally as a suppository (eg, bisacodyl). However, they may cause abdominal cramping and fluid and electrolyte disturbances, especially if rectal impaction is present. Stimulant laxatives should be used short-term because they can cause dependency.

Stool softeners (eg, docusate sodium) help soften hard stools but provide little relief for constipation. In bed-ridden patients, defecation may be an even more unpleasant experience for patients and caregivers. Mineral oil should generally be reserved for only the most serious cases, because its use can result in aspiration or anal seepage in some patients; long-term use can result in vitamin malabsorption.

Enemas can be used when fecal impaction is present. Plain tap water enemas or sodium phosphate and biphosphate enemas can be used. Soapsuds enemas produce mucosal damage and cramping and should be avoided. Because rectal volumes increase with age, the enema should generally contain about 500 to 1000 mL. After the initial blockage has been removed manually and with enemas, colonic cleansing with polyethylene glycol-electrolyte solutions (which are administered orally or via nasogastric tube) is helpful to remove more proximal colonic stool collections.

Still other approaches may be necessary. Patients with refractory constipation may require referral for specialized testing and treatment. Patients with severe slow transit constipation may benefit from subtotal colectomy. Biofeedback may help patients with pelvic floor dysfunction.