Diet and Drugs in Colorectal Surgery ( Part 3 ) The End

Thursday, July 12, 2012

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Editors: Corman, Marvin L.

Title: Colon and Rectal Surgery, 5th Edition

Copyright ©2005 Lippincott Williams & Wilkins

Short Bowel Syndrome

Patients who have undergone resection of the small intestine, particularly the distal ileum, may present with symptoms of urgency and diarrhea (especially after meals), weight loss, or dehydration. When an extensive portion of the small intestine has been resected, there may be insufficient surface area available for absorption of nutrients. It has been estimated that the minimal length of small intestine necessary to sustain adequate enteral nutrition is approximately 1 m, although the presence of the colon my reduce that requirement. Preservation of the proximal bowel (duodenum and jejunum) appears more likely to facilitate nutrient absorption than does the presence of ileum, with the exception of certain specific nutrients, such as vitamin B12. Those individuals who are unable to achieve adequate enteral nutrition require parenteral hyperalimentation (see Chapter 30).

Studies have demonstrated that the colon actually is able to absorb a reasonable amount of calories, largely in the form of short-chain fatty acids.30 In addition to providing nutrient value to the cells of the colonic mucosa itself, 500 kcal/day may actually be absorbed into the systemic circulation.

It has been demonstrated by utilizing growth hormone and glutamine, with a diet of increased carbohydrates and decreased fat, that this combination is associated with an increase in the absorption of protein and a decrease in stool output.7 In some individuals with small intestine too limited to provide adequate absorptive area, this regimen has been able to decrease or completely eliminate the need for parenteral hyperalimentation.

The proximal duodenum is the most efficient area of absorption of most nutrients, but jejunum and ileum can adapt and increase absorption. This has been demonstrated following duodenal resection or bypass, provided there is adequate time for mixing of bile and pancreatic secretions with the ingested food. The distal ileum is the primary absorptive area for bile salts and vitamin B12, so that removal of this area can result in cholerrheic diarrhea and vitamin B12 deficiency.

Those individuals who have undergone small bowel resection but still have adequate surface area for absorption may initially experience symptoms of rapid transit and diarrhea. In most cases, the remaining bowel can adapt to allow adequate nutrition, although a period of adjustment may be necessary. As previously suggested, patients with 100 cm of small bowel remaining should be able to subsist on an elemental diet, but the palatability of predigested food is very poor. Only very highly motivated individuals can tolerate oral elemental feedings, so usually a nasogastric tube, gastrostomy, or jejunostomy tube is required to achieve adequate caloric intake. With this regimen, patients often suffer an initial period of frequency, bloating, and loose stools. These symptoms gradually improve with time. Supplemental liquid nutrition given between meals may help maintain body weight. Additional therapy, including bile salt–binding resins and loperamide or diphenoxylate, will slow transit and should help improve absorption. The typical patient will initially suffer weight loss, but ultimately achieve a new steady state at lower body mass. With this type of patient, oral intake is usually adequate to maintain metabolic balance. It is rare that parenteral nutrition will be required, and with appropriate management, individuals should be able to maintain a positive metabolic balance. However, those who have an inadequate small bowel surface area for absorption of nutrients will require some form of supplementation or parenteral nutrition.

Cholerrheic Diarrhea

Individuals who have undergone resection of the distal ileum, particularly if the ileocecal valve is removed, may exhibit symptoms of cramping, bloating, and diarrhea, often accompanying intake of food. The etiology of these complaints is not clear, but it appears to be related to deconjugation of nonabsorbed bile salts by the colonic bacteria. Deconjugated bile salts are toxic to the lining of the colon; they initiate fluid and electrolyte secretion and lead to symptoms of cramping and diarrhea (cholerrheic diarrhea). This theory is supported by the observation that bile salt–binding medications, such as cholestryamine, often ameliorate the symptoms associated with distal ileal resection and cholerrheic diarrhea. The dosage can be adjusted to achieve normal bowel movements without induction of constipation. Additional reduction in diarrhea can be afforded by the use of loperamide or diphenoxylate in those individuals whose diarrhea persists despite bile salt–binding medications.

Postoperative Ileus

Ileus is a common consequence of any abdominal operation and, obviously, of any operation on the intestinal tract. It may occur after minor surgical procedures, even those outside the abdomen, but it is clearly related to intraabdominal surgery.3 Why this occurs is not entirely clear, but it is thought to be due to the effects of the anesthetic, manipulation of the bowel, a generalized increase in sympathetic tone, or the opiates that may be used to control postoperative pain.29 The effects of bowel manipulation are controversial, but it appears that less invasive surgical procedures are associated with less severe postoperative ileus. This, of course, is a contention of the advantage of minimally invasive surgery (see Chapter 27). The effects of the ileus appear most pronounced on the colon, with the small bowel and the stomach recovering function earlier.

Treatment

I do not presume to tell surgeons how to manage patients who have postoperative ileus. However, certain points are worth emphasizing, at least from the perspective of a gastroenterologist. Studies evaluating the efficacy of prokinetic agents (erythromycin, metoclopramide, and cisapride) have failed to generate consistent results that could suggest a reduced duration of postoperative ileus.4,20,35,40 This lack of an effective medical approach mandates modification of oral intake following surgery. Most surgeons wait for evidence of bowel activity (the passage of flatus, the presence of bowel sounds, or a bowel movement) before resuming oral feedings. However, recent evidence suggests that one may, with caution, commence oral intake a lot sooner than had been previously recommended. This is based to some extent on the evidence gleaned from early alimentation following laparoscopic procedures.

There is no evidence that nasogastric tube suction in the absence of vomiting provides any benefit, but patients with distension and vomiting will have these symptoms ameliorated by gastric suction (see Chapter 22). With a nasogastric tube in place, the volume of aspirate can be ascertained, and this can be utilized as a guide for the initiation of oral feedings. Although there is a reasonable difference of opinion concerning when to remove the tube, the volume should be less than 50 mL/hr before it is eliminated. Alternatively, clamping the tube for several hours or overnight and measuring the residual gastric fluid comprise a useful guide. If the residual is less than 100 mL after clamping for 4 hours, bowel activity may be presumed to have developed.

Clear liquids are usually offered initially, although the rationale for this concept remains murky. For example, there is no evidence to suggest that a regular diet should be initially avoided. This may be largely a consequence of the fact that it is easier to aspirate gastric retention if there is no residual solid material present. Diet is then advanced as tolerated, usually to a full liquid diet and then to a selected diet. However, certain clear liquids may produce untoward symptoms. For example, fruit juices that contain poorly absorbed carbohydrates, especially fructose, may lead to distension, bloating, and diarrhea. Apple juice, a staple in the clear liquid diet, is a particularly offending agent. Caffeine is a well-known gastric irritant. This may lead to substernal burning and to nausea. Full liquid diets may be high in dairy products and lactose. As mentioned, 65% of adults have varying degrees of intolerance to these substances.

A similar approach to avoiding items that may lead to dietary intolerance should be employed when enteral tube feedings are used. Tube feedings occasionally can cause diarrhea, possibly from the high osmolality of the feedings or to rapid feedings. However, the etiology of diarrhea is multifactorial and in the postoperative patient may include antibiotic use, the vehicles used to make medication soluble, the fact that it may be delivered by a tube, particularly sorbitol,14 intraabdominal infection, and the consequences of an anastomosis. Avoiding poorly tolerated carbohydrates, including fructose, lactose, lactulose, and sorbitol, can minimize the bowel discomfort often experienced by patients in the postoperative period.

Diverticular Disease

Diverticular disease is a frequently encountered condition in developed countries. The prevalence appears to be over 30% in adults over the age of 50 and rises with advancing age.32 The presence of the mucosal herniations thorough the bowel wall is thought to be a consequence of decreased dietary fiber, a finding supported by epidemiologic data (see the discussion on diet in Chapter 26). In countries where the intake of dietary fiber is five to ten times that of the United States, diverticular disease is a rare finding.6,30 Patients with diverticulosis are usually asymptomatic, but abdominal pain has been attributed to spasm often seen in the presence of diverticula. Because IBS is found in approximately 12% of adults in the United States, it is not clear whether diverticulosis or IBS is responsible for the cramping abdominal pain in these individuals.31 In one study, the poorly absorbed oral antibiotic, rifaximin, when given with fiber supplementation, reduced the discomfort of diverticular disease.31

Increasing dietary fiber is associated with an increase in the water content of stool and may ease its passage through the colon. If the theory that diverticula are more likely to occur in the setting of increased intraluminal pressure is correct, increased fiber should reduce the likelihood of new diverticula forming, but not eliminate the diverticula already present. Despite conventional wisdom, there is no evidence to suggest that seeds, nuts, popcorn husks, and other small, sharp, or firm food contents are responsible for acute attacks of diverticulitis. Furthermore, eliminating these products from the diet does not confer protection from future attacks.

When patients are experiencing the symptoms of diverticulitis, luminal narrowing is associated with distension, bloating, and alterations in bowel habits. With acute diverticulitis, reducing stool volume should decrease discomfort associated with the partial blockage of the bowel. Dietary therapy consists of clear liquid diet until normal fecal flow is established, followed by resumption of a high-fiber diet (if tolerated) once the inflammation has subsided. These measures are used to reduce bloating and distension, but the treatment of the acute episode remains broad-spectrum antibiotics.13 Any one of a number of antibiotics is useful in this acute inflammatory condition, with surgery required for complications (see Chapter 26).

Chemoprophylaxis

Recent studies have renewed one's interest in probiotics, minerals, and NSAIDs in the prevention of gastrointestinal problems. Some of the more definitive therapies are discussed in the next sections.

Pouchitis

Patients who have undergone proctocolectomy with reservoir-anal procedures or continent pouches often present with inflammatory changes in the reservoir, a consequence of what has been attributed to bacterial overgrowth (see Chapter 29). Successful treatment usually consists of antibiotics such as metronidazole, 250 mg three times daily, or ciprofloxacin, 500 mg twice daily. However, some patients experience recurrent bouts of pouchitis that may be difficult to control. Studies using a probiotic, VSL-3, have suggested a prolonged remission from pouchitis with this combination of bacteria.15 The preparation contains multiple strains of bacteria that, theoretically, replenish the gut flora consortium that help to preserve a healthy colon mucosa. The medication is available online at http://www.questcor.com.

Colon Polyps and Cancer Prevention

Anecdotal reports and case-control studies suggest that patients taking aspirin, fiber, and vitamins and who consume vegetarian and low-fat diets have a reduced incidence of colon polyps. This has spurred interest in polyp chemoprevention. However, initial studies failed to demonstrate benefit with supplementary vitamins E, C, and β-carotene, as well as with fiber supplementation. A randomized, controlled trial found a reduction in new polyp formation though the use of calcium supplements.1 Patients were given 1,200 mg of elemental calcium. Those so treated had an adjusted risk ratio for the formation of new polyps of 0.85 compared with the placebo-treated population.

Reports that sulindac reduced the development of adenomatous polyps in familial adenomatous polyposis syndrome, as well as case-control studies in aspirin users, further stimulated interest in the use of NSAIDs to reduce new polyp formation. Prospective, randomized, controlled studies have suggested a reduction in the formation of new neoplastic polyps in patients with prior colorectal cancer or adenomas through the use of aspirin. Patients with previous colorectal cancer were placed on 325 mg of aspirin daily. They had an adjusted relative risk of forming new polyps of 0.65 compared with placebo-treated patients.2 In the second study, two doses of aspirin, 325 mg or 81 mg, were compared with a placebo in preventing new polyps in patients with prior adenomas. Low-dose aspirin was associated with a modest risk reduction (0.81) compared with a placebo, but the regular aspirin tablet was no better than a placebo.36 These studies suggest a modest effect of NSAIDs in reducing the formation of new polyps in patients prone to development of adenomas. However, the high rate of upper gastrointestinal complications associated with the use of NSAIDs, coupled with only a modest reduction in new polyp incidence, makes it difficult for one to advocate aspirin therapy at this time for this indication.

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