Porth's Essentials of Pathophysiology, 4e

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Gastrointestinal and Hepatobiliary Function

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serious in infants and small children, persons with other illnesses, and the elderly. Thus, the replacement of fluids and electrolytes is considered to be a primary therapeutic goal in the treatment of diarrhea. Oral replacement ther- apy (ORT) can be used in situations of uncomplicated diarrhea that can be treated at home. First applied to the treatment of diarrhea in developing countries, ORT can be regarded as a case of reverse technology, in which the protocols originally implemented in these countries have changed health care practices in industrialized countries as well. 42 Complete ORT solutions contain carbohydrate, sodium, potassium, chloride, and base to replace that lost in the diarrheal stool. 42,46 Commonly used beverages such as apple juice and cola drinks, which have increased osmo- larity because of their high carbohydrate and low electro- lyte content, are not recommended. The effectiveness of ORT is based on the coupled transport of sodium and glucose or other actively transported small organic mol- ecules. ORT can be particularly effective in treating dehy- dration associated with diarrheal diseases in infants and small children. Children who are severely dehydrated with changes in vital signs or mental status require emergency intravenous fluid resuscitation. After initial treatment with intravenous fluids, these children can be given ORT. Evidence suggests that feeding should be continued during diarrheal illness, particularly in children. 46 Starch and simple proteins are thought to provide co-transport molecules with little osmotic activity, increasing fluid and electrolyte uptake by intestinal cells. The luminal contents associated with early refeeding are also known to contain growth factor for enterocytes and help facili- tate repair after injury. It is recommended that children who require rehydration therapy because of diarrhea be fed an age-appropriate diet. Although there is little agreement on which foods are best, fatty foods and foods high in simple sugars are best avoided. Almost all infants with acute gastroenteritis can tolerate breast- feeding. For formula-fed infants, diluted formula does not provide an advantage over full-strength formula. Drugs used in the treatment of diarrhea include diphenoxylate (Lomotil) and loperamide (Imodium), which are opium-like drugs. These drugs decrease gas- trointestinal motility and stimulate water and electro- lyte absorption. Adsorbents, such as kaolin and pectin, adsorb irritants and toxins in the bowel. These ingredi- ents are included in many over-the-counter antidiarrheal preparations because they adsorb toxins responsible for certain types of diarrhea. Antidiarrheal medications should not be used in persons with bloody diarrhea, high fever, or signs of toxicity because of the risk of worsen- ing the disease. Antibiotics should be reserved for use in persons with identified enteric pathogens. Constipation Constipation can be defined as the infrequent or difficult passage of stools. 47–49 The difficulty with this definition arises from the many individual variations of function that are normal. What is considered normal for one person (e.g., two or three bowel movements per week) may be considered evidence of constipation by another.

CHART 29-1   Chronic Diarrhea

Hyperosmotic diarrhea Saline cathartics Lactase deficiency Secretory diarrhea

Acute infectious diarrhea Failure to absorb bile salts Fat malabsorption Chronic laxative abuse Carcinoid syndrome Zollinger-Ellison syndrome Fecal impaction Inflammatory bowel disease Crohn disease Ulcerative colitis Infectious disease Shigellosis Salmonellosis Irritable bowel syndrome

Secretory diarrhea occurs when the secretory processes of the bowel are increased. Secretory diarrhea also occurs when excess bile acids remain in the intestinal contents as they enter the colon. This often occurs with disease pro- cesses of the ileum because bile salts are absorbed there. It also may occur with bacterial overgrowth in the small bowel, which interferes with bile absorption. Inflammatory diarrhea commonly is associated with acute or chronic inflammation or intrinsic disease of the colon, such as ulcerative colitis or Crohn disease. Inflammatory diarrhea usually is evidenced by frequency and urgency and colicky abdominal pain. It commonly is accompanied by tenesmus (i.e., ineffectual and painful straining at stool), fecal soiling of clothing, and awaken- ing during the night with the urge to defecate. Chronic parasitic infections may cause chronic diar- rhea through a number of mechanisms. Pathogens most commonly associated with chronic diarrhea include the protozoans Entamoeba histolytica, Giardia, and Cyclospora. Immunocompromised individuals are particularly susceptible to infectious organisms such as Cryptosporidia, cytomegalovirus (CMV), and Mycobacterium avium-intracellulare complex that can cause both acute and chronic diarrhea (see Chapter 16). Diagnosis andTreatment. The diagnosis of diarrhea is based on complaints of frequent stools and a history of accompanying factors such as concurrent illnesses, med- ication use, and exposure to potential intestinal patho- gens. Disorders such as Crohn disease and ulcerative colitis should be considered. If the onset of diarrhea is related to travel outside the United States, the possibility of traveler’s diarrhea must be considered. Although most acute forms of diarrhea are self-limited and require no treatment, diarrhea can be particularly