Constipation
Constipation is a condition in which a person has uncomfortable or infrequent bowel movements.
Constipation may be acute or chronic. Acute constipation begins suddenly and conspicuously. Chronic constipation may begin insidiously and persist for months or years.
A person with constipation often or always produces hard stools that may be difficult to pass. The person also may feel as though the rectum has not been completely emptied. Bowel movements are likely to be infrequent as well. Many people believe they are constipated if they do not have a bowel movement (defecate) every day. However, daily bowel movements are not normal for everyone, and having less frequent bowel movements does not necessarily indicate a problem unless there has been a substantial change from previous patterns. The same is true of the color and consistency of stool; unless there is a substantial change, the person probably does not have constipation.
Causes
Slowed Transit of Stool: Constipation tends to occur when the transit (passage) of stool along the large intestine slows. Under normal circumstances, water is pulled from the stool as it passes through the large intestine. Slowed transit of stool allows the large intestine to pull more water from the stool, resulting in the hard, dry stools and associated difficult passage of stools that characterize constipation.
Drugs that slow transit, including aluminum hydroxide (common in over-the-counter antacids), bismuth subsalicylate, iron salts, anticholinergic drugs, certain antihypertensives, opioids, and many sedatives, frequently cause constipation. Because physical activity helps the intestines move stool along, lack of activity tends to slow transit and lead to constipation. For this reason, people who are confined to bed because of illness often are constipated.
Disorders and diseases that can slow transit time of stool include an underactive thyroid gland (hypothyroidism), high blood calcium levels (hypercalcemia), and Parkinson's disease. People with diabetes often develop a condition in which parts of the digestive system slow down. Other conditions, including poor blood supply to the large intestine and nerve or spinal cord injury, can also cause constipation by slowing transit.
In an extreme case of slowed transit, called colonic inertia (inactive colon), the large intestine stops responding to the stimuli that usually cause bowel movements: eating, a full stomach, a full large intestine, and stool in the rectum. A decrease in contractions in the large intestine or an insensitivity of the rectum to the presence of stool results in severe, chronic constipation. Colonic inertia often occurs in people who are older, debilitated, or bedridden, but it can occasionally occur in otherwise healthy younger women (and, much less commonly, in healthy younger men). Colonic inertia sometimes occurs in people who habitually delay moving their bowels or who have used laxatives or enemas for a long time.
Dehydration and Low-Fiber Diet: Dehydration causes constipation because the body tries to conserve water in the blood by removing additional water from the stool. Lack of fiber (the indigestible part of food) in the diet can lead to constipation because fiber helps hold water in the stool and increases its bulk, making it easier to pass.
Obstruction: Constipation is sometimes caused by obstruction of the large intestine. Obstruction can be caused by cancer, especially in the last portion of the large intestine, if it blocks the movement of stool. Bezoars (tightly packed collections of partially digested or undigested material) and foreign bodies can also block the intestinal tract (see Section 9, Chapter 123). People who previously had abdominal surgery may develop obstruction, usually of the small intestine, because of formation of bands of fibrous tissues (adhesions).
Dyschezia: Dyschezia is difficulty in defecating caused by an inability to control the pelvic and anal muscles. Having a normal bowel movement requires relaxing the pelvic floor muscles (the muscles that support the bladder, uterus, and rectum) and the circular muscles (sphincters) that keep the anus closed. Otherwise, efforts to defecate are futile, even with severe straining. People with dyschezia sense the need to have a bowel movement but cannot. Even stool that is not hard may be difficult to pass.
Conditions that can cause dyschezia include pelvic floor dyssynergia (a disturbance of muscle coordination), anismus (a failure of the sphincter muscles to relax during defecation), rectocele (hernia of the rectum into the vagina), enterocele (hernia of the small intestine into the rectum), rectal ulcer, and rectal prolapse.
Aging: Constipation is particularly common among older people. Age-related changes in the large intestine (see Section 9, Chapter 118) along with increased use of medications and reduced physical activity tend to slow the transit of stool through the large intestine. Slowed transit is particularly common during periods of illness. The rectum enlarges with age, and increased storage of stool in the rectum allows hard stool to become impacted.
Pain and Psychogenic Factors: Chronic pain and psychologic conditions, especially depression, are common causes of acute and chronic constipation. Constipation may result from changes in the levels of certain substances in the brain, such as serotonin, that can affect the intestinal tract.
Symptoms and Complications
Constipation can cause abdominal pain. The pain may occur only when straining during a bowel movement, although in some people the pain persists between bowel movements. Constipation can cause nausea and impair appetite.
Straining during a bowel movement increases pressure on the veins around the anus and can lead to hemorrhoids. Straining also increases blood pressure, which, although only temporary, may be extreme.
Constipation is one of the major risk factors for the development of diverticular disease. The walls of the large intestine are damaged by the increased pressure required to move small hard stools. Damage to the walls of the large intestine leads to the formation of balloon-like sacs (diverticula), which can become clogged and inflamed.
Fecal impaction, in which the stool in the last part of the large intestine and rectum hardens and blocks the transit of other stool, sometimes develops in people with constipation. This condition is particularly common among older people, pregnant women, and people with colonic inertia. Fecal impaction leads to cramps, rectal pain, and strong but futile efforts to defecate. Often, watery mucus or liquid stool oozes around the blockage, sometimes giving the false impression of diarrhea. Fecal impaction can aggravate or further worsen constipation.
Diagnosis
When constipation develops in someone who has not had it before and there is not an easy explanation, such as a change in diet or physical activity or new use of one of the many drugs known to cause constipation, a doctor may perform blood tests to check for an underactive thyroid gland (hypothyroidism) or high calcium levels in the blood (hypercalcemia), both of which can cause constipation. If there is any question about cancer as a cause, a barium enema x-ray study or colonoscopy is performed.
Prevention and Treatment
Constipation is best prevented and treated with a combination of adequate exercise, a high-fiber diet, an adequate intake of fluids, and the occasional use of laxatives. When a potentially constipating drug has been prescribed, a laxative along with increased intake of dietary fiber and fluids helps to prevent constipation.
Vegetables, fruits, and bran are excellent sources of fiber. Many people find it convenient to sprinkle 2 or 3 teaspoons of unrefined miller's bran on high-fiber cereal or fruit 2 or 3 times a day. To work well, fiber must be consumed with plenty of fluids.
When an underlying disease is causing constipation, the disease must be treated.
Dyschezia is not easily treated with laxatives. Relaxation exercises and biofeedback are used for pelvic floor dyssynergia and are effective for some people. Surgery may be needed to repair an enterocele or a large rectocele.
Fecal impaction cannot be treated with diet or easily with laxatives. The hard stool usually has to be removed by a doctor or nurse using a gloved finger. Sometimes, the impaction can be resolved with an enema.
Overzealous treatment, especially the long-term use of stimulant laxatives, irritant suppositories, and enemas, can lead to diarrhea, dehydration, cramps, or dependence on laxatives.
Laxatives: Many people use laxatives to relieve constipation. Some laxatives are safe for long-term use; others should be used only occasionally. Some are good for preventing constipation; others can be used to treat it.
Bulking agents, such as bran and psyllium (also available in the fiber of many vegetables), add bulk to the stool. The increased bulk stimulates the natural contractions of the intestine, and bulkier stools are softer and easier to pass. Bulking agents act slowly and gently and are among the safest ways to promote regular bowel movements. These agents generally are taken in small amounts at first. The dose is increased gradually until regularity is achieved. People who use bulking agents should always drink plenty of fluids.
Stool softeners, such as docusate, increase the amount of water that the stool can hold. Actually, these laxatives are detergents that decrease the surface tension of the stool, allowing water to penetrate the stool more easily and soften it. In addition, the slightly increased bulk that results from these drugs stimulates the natural contractions of the large intestine and thus promotes easier elimination. Some people, however, find the softened nature of the stool unpleasant. These softeners are best reserved for people who must avoid straining, for example, people with hemorrhoids or people who recently underwent surgery.
Osmotic agents pull large amounts of water into the large intestine, making the stool soft and loose. The excess fluid also stretches the walls of the large intestine, stimulating contractions. These laxatives consist of salts or sugars that are poorly absorbed. They may cause fluid retention in people with kidney disease or heart failure, especially when given in large or frequent doses. Osmotic agents containing magnesium and phosphate are partially absorbed into the bloodstream and can be harmful in people with kidney failure. These laxatives generally work within 3 hours. They are also used to clear stool from the intestine before x-rays of the digestive tract are taken or before colonoscopy is performed.
Stimulant laxatives contain irritating substances, such as senna and cascara, that directly stimulate the walls of the large intestine, causing them to contract and move the stool. Taken by mouth, stimulant laxatives generally cause a semisolid bowel movement in 6 to 8 hours but often cause cramping as well. In suppositories, these laxatives often work in 15 to 60 minutes.
Prolonged use of stimulant laxatives can create abnormal changes in the lining of the large intestine caused by deposits of a pigment (a condition called melanosis coli). Also, stimulant laxatives can become addictive, leading to the development of lazy bowel syndrome, which in turn causes the large intestine to become dependent on the laxatives. For all these reasons, stimulant laxatives should be used only for brief periods of time to treat constipation. They are useful for preventing constipation in people who are taking drugs that will almost certainly cause constipation, such as opioids. Stimulant laxatives are often used to empty the large intestine before diagnostic procedures are performed.
 See the drug table Drugs Used to Prevent or Treat Constipation.
Enemas: Enemas mechanically flush stool from the rectum and lower part of the large intestine. Small-volume enemas can be purchased in squeeze bottles at a pharmacy. They can also be administered with a reusable squeeze-ball device. However, small-volume enemas are often inadequate, especially in older people, whose rectal capacity increases as advancing age makes the rectum more easily stretched. Larger-volume enemas are administered with an enema bag.
Plain water is often the best fluid to be used as an enema. The water should be room temperature to slightly warm, but not hot or cold. Water (in volumes of about 5 to 10 fluid ounces [150 to 300 milliliters]) is gently directed into the rectum; adding additional force is dangerous. The water is then expelled, washing stool out with it.
Prepackaged enemas often contain small amounts of salts, often phosphates. Appropriate salts can also be added to homemade enemas. They offer little advantage, however, to plain water.
The addition of small amounts of soap to the water (soap-suds enema) adds the stimulant laxative effects of soap. Soap-suds enemas are sometimes useful when plain water enemas fail, but they can cause cramping.
Many other substances, including mineral oil, are sometimes added to water-based enemas. However, they offer little advantage.
Very large volume enemas, called colonic enemas, are rarely used in medical practice. Doctors use colonic enemas only in people with very severe constipation (obstipation). Some practitioners of alternative medicine use colonic enemas in the belief that cleansing the large intestine is beneficial. Tea, coffee, and other substances are often added to colonic enemas but have no proven health value and may be dangerous.
| 
