Diet and Drugs in Colorectal Surgery
John L. Petrini Jr.
A drug is a substance that, when injected into a rat, produces a scientific paper.
—Anonymous
The role of diet in a healthy bowel has been a stimulating and controversial subject for two millennia. There are data to support numerous statements and recommendations, but controlled clinical trials defining the benefits of various foods and therapies are quite limited. In general, diets high in fiber and roughage help facilitate the normal passage of stool. In addition, they may be beneficial to the overall health of an individual by reducing cholesterol, maintaining blood sugar in the normal range, and decreasing the incidence of diverticulosis. Cruciferous plants also contain anticarcinogens that may reduce the incidence of colonic neoplasms. Furthermore, aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) appear to reduce the incidence of colon cancer. Other claims—for example, that cow’s milk and dairy products may be harmful for young children and most adults— have some validity. There are a host of other hypotheses, but the data in support of them are very weak.
Patients may solicit the opinion of a physician for concerns that do not necessarily require surgical intervention, or they may experience gastrointestinal symptoms that are consequences of an operation. For many, dietary manipulations and medical therapy may provide relief of the discomfort and disability. Initial therapy for most disorders of the colon and rectum often includes dietary adjustment. This approach is typically instituted by the patient himself or herself. The symptoms of certain conditions, such as irritable bowel syndrome (IBS), inflammatory bowel disease, diverticulitis, diarrhea, and constipation, can often be ameliorated by dietary manipulation, even though the cause of the disorder may not be related to a specific food. The addition of medication, either for symptomatic relief or to treat the specific disease state, may also contribute to the relief of a patient’s symptoms. It is important, however, to understand the pathophysiology underlying the bowel symptoms in order to offer the appropriate treatment. Unfortunately, there is a paucity of information available for many disorders affecting the gastrointestinal tract that may aid the physician in appropriate therapeutic decision making. This chapter focuses on some of the more common symptoms and conditions for which patients seek the attention of physicians trained in gastrointestinal disease and gastrointestinal surgery.
▶ BOWEL MANAGEMENT PROBLEMS
Constipation
Constipation can be defined as either a decrease in the frequency of stools or an increase in the difficulty of passage of stool. Patients may also complain of hard bowel movements, small actions, inability to evacuate, or the sensation of incomplete evacuation. Some studies have demonstrated that 95% of healthy adults will have a minimum of three bowel movements per week.24,33 Those with fewer than three stools a week are considered to have “constipation,” but they may not be truly symptomatic or seek medical attention. Those who do request help usually complain of either decreased frequency or difficulty in passing stool. Therapy is therefore directed at either increasing the water content (i.e., softening the stool) or increasing the frequency of bowel movements.
History
In order to make a recommendation concerning therapy, a carefully obtained history is essential. This should include the duration of the complaints, dietary habits, the use of medications, and lifestyle. These often provide the information
necessary to arrive at the source of the patient’s complaints. It is not within the purview of this chapter to present a complete discussion of all the disease states, endocrine abnormalities, medications, neurologic disorders, and dietary issues that are associated with constipation. However, it is important to note the more common endocrine conditions that may affect the bowels and that should be considered: hypothyroidism, diabetes mellitus, and hyperparathyroidism. Other diseases that predispose to constipation include uremia, porphyria, amyloidosis, and short-segment Hirschsprung’s disease.
necessary to arrive at the source of the patient’s complaints. It is not within the purview of this chapter to present a complete discussion of all the disease states, endocrine abnormalities, medications, neurologic disorders, and dietary issues that are associated with constipation. However, it is important to note the more common endocrine conditions that may affect the bowels and that should be considered: hypothyroidism, diabetes mellitus, and hyperparathyroidism. Other diseases that predispose to constipation include uremia, porphyria, amyloidosis, and short-segment Hirschsprung’s disease.
As mentioned, medications are a frequent cause of constipation, so it is important to obtain a history of all medications used, including those available over the counter. Although the list is extensive, the more common ones to consider include the opiate/analgesics, antipsychotics (particularly the monoamine oxidase inhibitors and tricyclic antidepressants), anticholinergics, iron and other heavy metals, antacids, anticonvulsants, calcium channel blockers, and diuretics.
Evaluation
The perineum should be carefully inspected for obvious pathologic entities that may impede the passage of stool. Instrument examination, contrast studies, transit studies, gynecologic examination, ultrasonography, computed tomography, and physiologic studies may be required in selected patients. Certainly, gastrointestinal evaluation at some point must be accomplished to rule out the presence of a specific etiologic factor. These are discussed in the following chapters.
Treatment
The standard treatment of nonspecific constipation begins with dietary manipulation, usually through increasing dietary fiber and fluid intake. In addition, several classes of medication are available to increase stool water or stool frequency. These include bulk laxatives, stool softeners, osmotic or saline laxatives, cathartics, and motility-enhancing drugs (prokinetics).
Those who have constipation usually benefit from increasing the water content of the stool by increasing their intake of fiber and water. It is well known that individuals who live in so-called developing countries consume a large amount of unprocessed fiber. However, the diet in most developed countries contains inadequate roughage or unprocessed dietary fiber.6,17 Dietary fiber consists of plant products that are not digested or absorbed by the small intestine. These include cellulose, lignin, gums, pectins, hemicelluloses, and polysaccharides. Increasing fluid intake without adding fiber to the diet is usually ineffective for correcting constipation. Fiber, however, will improve stool consistency irrespective of the water intake.46 Interestingly, fiber with small amounts of water can be used to treat diarrhea. Some foods, particularly dairy products, actually decrease stool water content and contribute to constipation. Good sources of dietary fiber include fresh fruits and vegetables, whole grain cereals, and unprocessed carbohydrates such as bran, whole wheat, and brown rice (Table 4-1). Total daily fiber intake should be adjusted to approximately 30 g or more if tolerated by the patient.
Fiber Products
Those individuals whose diet remains inadequate in fiber can increase stool water-carrying capacity by adding a fibercontaining bulk laxative. Psyllium husk, either as powder or granules, is obtained from various species of plantain. Bran is a product of the milling of wheat. Flax seed and ground flax seeds are high sources of fiber as lignins. These products, when taken with adequate dietary water, will provide additional bulk to the stool and increase the water content, trapping it in a mucin within the stool.
TABLE 4-1 Fiber Content of Selected Dietary Items | ||||||||||||||
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Other bulk laxatives use hydrophilic substances, such as polycarbophil and powdered karaya (sterculia) gum. The amount of bulking agents can be adjusted to what is required to alleviate the patient’s constipation. This range is usually between 4 and 10 g/day, with the administration divided if a higher dose is required.
The major disadvantage of bulking agents is the bloating and gas commonly associated with the cellulose and ligninbased products. Fiber products with a base of hemicellulose or pectin seem to reduce these side effects, as does the use of the polycarbophil bulk agents. However, patients seem to require higher doses of the latter than of the cellulose-based products in order for similar results to be achieved. One of the side benefits of the use of bulk agents is the lowering of serum cholesterol. This is probably effected through the binding of bile salts and reducing their reabsorption, so that the bile salt pool is lowered. Problems associated with the use of bulking agents include intestinal obstruction and fecal impaction, particularly if there is an underlying pathologic entity. Additionally, allergic reactions have been reported.
Stool Softeners
Patients who are resistant to the bulking agents alone can increase the water content further with stool softeners or
emollients. The principal agent is docusate (dioctyl sulfosuccinate), which is available as the sodium, calcium, or potassium salt. These products inhibit the normal water-absorptive capacity of the colon while producing only a minimal decrease in the transit of fecal contents. Once one of these products has been administered, it may take 1 to 3 days to see an effect. In essence, they act to soften the stool but do not promote defecation. The usual adult dose is from 50 to 250 mg/day. Docusate should not be given with mineral oil because absorption of the oil as well as other medications is enhanced.
emollients. The principal agent is docusate (dioctyl sulfosuccinate), which is available as the sodium, calcium, or potassium salt. These products inhibit the normal water-absorptive capacity of the colon while producing only a minimal decrease in the transit of fecal contents. Once one of these products has been administered, it may take 1 to 3 days to see an effect. In essence, they act to soften the stool but do not promote defecation. The usual adult dose is from 50 to 250 mg/day. Docusate should not be given with mineral oil because absorption of the oil as well as other medications is enhanced.
Osmotic and Saline Laxatives
Should bulking agents and surfactants fail to enhance the passage of stool, the next preferred step would be to employ an osmotic or saline laxative. Magnesium phosphate, sodium sulfate, and potassium tartrate are poorly absorbed chemicals. Ingestion increases the stool water content through an osmotic effect. Surgeons are familiar with the use of saline laxatives for bowel preparations before operative or diagnostic procedures. In smaller doses, they can be used for their cathartic effect. Certain antacid products contain magnesium, and it is this agent that produces the side effect of diarrhea. There is, furthermore, some evidence that magnesium may actually increase motility of the small intestine through stimulation the release of cholecystokinin from the duodenum.15 The phosphate-containing solutions may cause a high serum phosphate level and impair cardiac contractility. They should therefore be used with caution in individuals with renal, cardiac, or hepatic disease. Dehydration can also be a consequence of the use of saline laxatives. Patients should be cautioned to take adequate fluids when using these agents.
Modified doses of colonic purgatives used to clear the colon prior to surgery and gastrointestinal procedures are also available to treat constipation.10 Miralax and Dulcolax Balance provide increased water to the colon by adding an osmotically neutral fluid to the gastrointestinal tract. The osmotically active agents, polyethylene glycol and a mixture of sodium and potassium sulfate, are not absorbed and remain in solution, carrying water to the colon. The usual dose is 17 g mixed with water; it can be given on a daily basis. There is minimal fluid or electrolyte shift, and side effects are rare.
Polysaccharides
Some carbohydrates are also poorly absorbed. This results in an osmotic effect that leads to enhanced water in the stool. These products include lactose, lactulose, and sorbitol. Lactulose has been particularly useful in the treatment of hepatic encephalopathy, but lower doses (30 to 60 mL/day) can be an effective laxative for patients with chronic constipation. Side effects include gas; bloating; cramps; flatulence; and, of course, fluid loss at high doses.
Lubricants
Mineral oil, a petroleum distillate, has been employed for the treatment of constipation. The mechanism of action appears to be penetration of the stool by the oil with resulting softening. However, because of the potential for complications, long-term use should be avoided. These include decreased absorption of fat-soluble vitamins and essential fatty acids. Furthermore, penetration of the mucosa can occur, and a foreign body reaction in the mesenteric lymph nodes, mucosa, and spleen has been reported. As previously mentioned, mineral oil should not be used with surfactants because there is the potential for increased absorption of the mineral oil.
Stimulant Laxatives
What rhubarb, senna or what purgative drug, would scour these English hence?
—William Shakespeare: Macbeth V, iii, 55
Cathartic laxatives are mucosally active agents that reduce net water and electrolyte absorption in addition to increasing bowel motility. The most frequently employed substances include phenolphthalein and the anthraquinone cathartics (senna, cascara sagrada, and danthron). These drugs act primarily to increase periodic mass movements within the colon and to decrease the segmental contractions that slow bowel activity. Generally, they become effective in 4 to 6 hours. The primary side effect, in addition to diarrhea, is that of cramping. Another drug, bisacodyl (Dulcolax), is a synthetic diphenylmethane that is similar to phenolphthalein. It is available not only for oral administration but also for rectal use. Because of the problem of gastric irritation, it is enteric coated. The standard adult dose is 10 to 15 mg.
Senna is an anthraquinone cathartic obtained from Cassia acutifolia or Cassia angustifolia. Preparations of the whole plant, leaflets, pods, and extracts are commercially available. Cascara sagrada is another anthraquinone; it is obtained from the bark of the buckthorn tree. Like all cathartics, these are variously effective depending on the dosage but can cause a problem with cramping. Furthermore, melanosis coli, a dark pigmentation of the colon mucosa, may be a consequence of long-term use of senna and cascara (see Figure 20-1).
Another cathartic, castor oil, is hydrolyzed in the small intestine to glycerol and ricinoleic acid. Ricinoleic acid acts in the small intestine by both decreasing net absorption of fluid and electrolytes and stimulating peristalsis. Because it is quite potent, it should be employed with special care. Long-term use should be avoided.
Motility Agents
Two agents are currently available that decrease transit time through acceleration of the muscular activity of the bowel. Gastrointestinal motility can be enhanced through the use of metoclopramide and erythromycin. Two other agents, cisapride and tegaserod, have been taken off the market in the United States. Metoclopramide and erythromycin have little or no effect on the colon and are not indicated for improving bowel function, but may be used for ameliorating gastric emptying.
Calcium Channel Stimulators
One medication approved for the treatment of constipation and constipation-predominate IBS is lubiprostone (Amitiza). Lubiprostone acts by stimulating intestinal chloride channels leading to fluid secretion. This increases intestinal motility. Lubiprostone is available in two doses, 8 µg and 24 µg, both given twice daily. The lower dose is approved for patients with IBS and pain that is associated with constipation, whereas the larger dose is indicated for chronic constipation.
Summary
Long-term use of intestinal stimulants and cathartics can lead to fluid and electrolyte disturbances, including dehydration, hypokalemia, hyponatremia, hypoalbuminemia, steatorrhea, protein-losing enteropathy, and secondary hyperaldosteronism. There is speculation that patients may become dependent on laxatives, and what is known as a “cathartic colon,”
or a chronically flaccid colon, may develop. However, there are no studies confirming that the presence or development of a so-called cathartic colon is a direct consequence of currently available laxatives or stimulants. A good general principle is that if laxatives are to be used, the lowest effective dose should be given. Long-term use should be discouraged. Most individuals will benefit from a program of increasing fiber and water content of the stool, with the addition of laxatives intermittently as needed to produce at least two or three bowel movements per week. The application of surgical intervention as a treatment for constipation should be offered only after an adequate trial of medical therapy and appropriate evaluation of the gastrointestinal tract (see Chapter 20).
or a chronically flaccid colon, may develop. However, there are no studies confirming that the presence or development of a so-called cathartic colon is a direct consequence of currently available laxatives or stimulants. A good general principle is that if laxatives are to be used, the lowest effective dose should be given. Long-term use should be discouraged. Most individuals will benefit from a program of increasing fiber and water content of the stool, with the addition of laxatives intermittently as needed to produce at least two or three bowel movements per week. The application of surgical intervention as a treatment for constipation should be offered only after an adequate trial of medical therapy and appropriate evaluation of the gastrointestinal tract (see Chapter 20).
Diarrhea
Diarrhea is a common complaint in numerous disorders, most of which are not attributable to colonic sources. A host of etiologic factors may produce an increase in stool water or stool frequency, including medications, infection, the consequences of radiation, hepatic or biliary disease, pancreatic insufficiency, intolerance to ingested food components, infiltration of the mucosa or submucosa with lymphocytes or eosinophils, neoplasm, inflammatory bowel disease, and IBS. It is beyond the scope of this chapter to offer a comprehensive discussion on the etiology and treatment of all the possible conditions that can lead to the symptom of diarrhea.
The most common presentation is that of increased stool water. This leads to loose stools, watery stools, and increased stool volume and/or frequency. The maximum number of bowel movements that is still considered within the normal range is three per day, assuming that this does not represent a change in the individual’s normal bowel habits. By definition, diarrhea is classified as acute until symptoms have been present for more than 6 weeks. After this time, it is considered chronic.
Acute Diarrhea
Acute diarrhea is often caused by medication or an infectious process, including bacterial enteritis, toxin ingestion, and infestation by the common intestinal parasites (e.g., Giardia, Cryptosporidium, Isospora). A discussion of the infectious and noninfectious colitidies can be found in Chapter 33. The use of broad-spectrum antibiotics, with resultant infection by Clostridium difficile, is a frequent source of acute diarrheal illness and represents one of the major hospital-acquired infections in the United States (see also Chapter 33).
Principles of Management
Treatment of acute diarrhea involves identification of the offending agent and initiation of whatever specific measures are necessary to eliminate the source or eradicate the organism. The use of medications that decrease gastrointestinal motility in acute, febrile diarrheal illnesses should be avoided because prolonged contact time can enhance the likelihood of transmucosal migration of the organism and systemic infection. A better alternative is the use of pectin or bismuth compounds, such as kaolin-pectin or bismuth subcitrate. These products bind shiga toxins and other cyclic guanosine monophosphate-stimulatory toxins associated with bacterial infection and decrease the net water and chloride secretion by the small bowel. If systemic signs and symptoms of infection are not present, the use of opiates to increase transit time and slow stool frequency offers symptomatic relief. By prolonging contact time with the intestinal tract, fluid and electrolyte absorption will be enhanced.
Chronic Diarrhea
Chronic diarrheal illnesses may be caused by a wide variety of disorders that affect the hepatobiliary system, pancreas, and small or large bowel. Individuals with chronic diarrhea present a challenge in differential diagnosis. This inevitably may lead to an extensive and expensive workup. Assuming that such an evaluation fails to establish a specific cause for the patient’s symptoms, the most likely disorder is the socalled IBS. Treatment for this complaint is to reduce the volume and frequency of bowel movements, so that the patient’s lifestyle can be improved.
Treatment
The approach to the management of patients with chronic diarrhea without a definable cause begins with a carefully taken dietary history. An offending food or substance may be found in the patient’s intake that increases the frequency of bowel action. For example, lactose-containing dairy products may induce symptoms of cramping or diarrhea in up to 65% of the adult population. Furthermore, caffeine-containing beverages may increase bowel activity and stool output. Additionally, sugarless candies, sodas, and fruits high in fructose or sorbitol may lead to symptoms of diarrhea. Therefore, removing the offending agent will usually improve symptoms.
Medical therapy encompasses a wide number of options. The following discussion focuses on those agents used specifically to treat diarrhea.
The fiber-containing bulk agents previously alluded to decrease stool water when they are given with less than the recommended volume of liquid. Any of the bulk agents taken under these circumstances decreases the absorption of water through the gastrointestinal tract. However, there are the side effects of bloating, gas, and cramping. Another means for binding stool water is through the use of bile salt-binding resins, such as cholestyramine (Questran). Bile salt-binding resins are the preferred drugs for the management of diarrhea associates with ileal resection.
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