Today's Veterinary Practice

MAY-JUN 2013

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GI InTerVenTIon: PATIenT wITh AcuTe DIArrheA | Table 1. Findings Used to Differentiate Small Bowel From Large Bowel Diarrhea FINDING SMALL BOWEL LARGE BOWEL Frequency of defecation Fecal volume Fecal mucus Fecal blood Tenesmus Urgency Dyschezia Vomiting Weight loss Steatorrhea normal to mildly increased normal to increased Absent Melena Absent Absent Absent May be present often present May be present Markedly increased Decreased often present hematochezia often present often present often present Infrequently present Infrequently present often present ence of increased numbers of these particles within the intestinal lumen leads to osmotic diarrhea. Osmotic diarrhea occurs with many malabsorptive disorders, such as exocrine pancreatic insufficiency, in which poorly digested nutrients are malabsorbed, remain within the GI lumen, and attract water. It can also occur with overeating and dietary indiscretion if poorly absorbed nutrients are ingested. Retention of nutrients in the GI tract can also lead to dysbiosis (see below) and fermentation of carbohydrates, which further increases the number of osmotically active particles. A hallmark of osmotic diarrhea is that it resolves when the patient stops ingesting poorly absorbable solute. 2. Secretory diarrhea: Stimulation of crypt enterocytes results in secretion of large volumes of fluid that exceeds the absorptive ability of the intestine. This occurs most commonly with infectious diseases, such as enteropathogenic Escherichia coli and salmonellosis, but is also a mechanism of diarrhea related to inflammatory bowel disease (IBD). By-products of dysbiosis can also stimulate intestinal secretion. One distinguishing feature of secretory diarrhea is its persistence despite fasting, which is due to abnormalities in ion transport not related to food. 3. Increased mucosal permeability: Increased permeability of the intestinal mucosa causes loss of fluids, electrolytes, proteins, and blood into the intestinal lumen. It commonly accompanies erosive, ulcerative, neoplastic (intestinal lymphoma), and inflammatory processes, such as IBD and hookworm infection. 4. Abnormal motility: Deranged motility is often secondary to disorders that cause diarrhea. Decreased segmental contractions result in transport of ingesta at a rate too fast for normal digestion and absorption. Platelet-activating factor, synthesized and released from several immunocytes, may be one of the inflammatory response mediators that stimulates giant aboral contractions, the powerful contractions that propagate—uninterrupted—from the small intestine to the ileum or colon. Tremendous fluid loss can occur when the small and/or large intestine are not functioning normally. Mild diarrhea causes few metabolic consequences; however, moderate or severe diarrhea can lead to profound dehydration, hypovolemic shock, electrolyte abnormalities (hypokalemia, hypochloremia, and hyponatremia), and acid–base disturbances. Metabolic acidosis typically develops secondary to loss of intestinal bicarbonate and dehydration leading to hypovolemia, anaerobic metabolism by tissues, and production of lactic acid. ACUTE DIARRHEA: CAUSES There are many causes of acute diarrhea in dogs and cats (Table 2, page 22). In many cases of acute diarrhea, signs resolve spontaneously or with symptomatic therapy without a specific cause being discovered. In animals with chronic diarrhea, a thorough diagnostic evaluation and appropriate dietary and therapeutic trials for diagnostic purposes are much more important. It is beyond the scope of this review to discuss causes and diagnostic approach to pets with chronic diarrhea; however, watch for evidence of chronicity even at first presentation of a pet with diarrhea. Endoparasites It is well documented that endoparasitism is primarily a concern in young animals.2,6-8 Batchelor, et al, documented that dogs with GI signs had a higher prevalence of intestinal parasites, including Giardia and Toxocara.6 In a referral population, however, dogs with GI signs had no greater odds of endoparasitism than healthy animals; instead, age and median household income were the strongest predictors of endoparasitism, and dogs from heavily populated ZIP codes had the greatest risk for endoparasitism.9 Dietary Indiscretion Dietary indiscretion is a common cause of acute diarrhea. One study reported that feeding a home-cooked diet, recent history of scavenging, or change of diet all increased the risk for diarrhea in dogs.10 Another study found a positive correlation between development of diarrhea and/or vomiting and reports of scavenging behavior (stealing food; eating trash; or eating feces from horses, farm animals, or cats).5 No correlation was found between GI signs and eating table food. Bacterial Enteritis A variety of bacteria are known or suspected to cause enteritis in dogs and cats (Table 2). Establishing a diagnosis of bacterial enteritis creates a significant challenge due to: • Limitations in understanding the complex intestinal microflora • Inadequate investigation of many potential pathogens. The fact that the microorganisms responsible for enteritis can be found in healthy individuals, and may not be found at a higher prevalence in animals with diarrhea, May/June 2013 Today's Veterinary Practice 21

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