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Definition

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The definition of diarrhea varies within the medical literature, so it is not surprising that patient perception of diarrhea varies as well. Many patients come to the ED complaining of “diarrhea” when what they really have is soft stools or two stools per day compared with their usual one.

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Acute diarrhea is the sudden onset of an increase in the normal water content of stool. In general, humans lose approximately 10 mL/kg/d of fluids in stool. The increased water content results in an increased frequency of stools from four to five times daily to >20 bowel movements in a 24-hour period. Strictly speaking, diarrhea is defined as an increased frequency of defecation, usually greater than three bowel movements per day for a daily stool weight exceeding 200 grams.1,2 Practically speaking, however, diarrhea is present when the patient is producing more stools of lesser consistency more frequently.

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Epidemiology

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Although diarrhea is no longer a significant cause of mortality in the U.S., it remains one of the leading causes of death worldwide. Diarrhea is thought to account for up to 5% of ED visits, more commonly in fall and winter. Despite the low U.S. mortality rate, diarrhea causes significant morbidity. In the U.S. alone, acute diarrhea is responsible for 211 million to 375 million episodes each year that equates to more than 900,000 hospitalizations.1 It is the second most common reason for work absenteeism and is estimated to cost $608 million dollars in lost productivity per year.3

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Pathophysiology

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There are four basic mechanisms of diarrhea: increased intestinal secretion, decreased intestinal absorption, increased osmotic load, and abnormal intestinal motility. Normally, the jejunum receives between 6 and 8 L per day of fluid in the form of oral intake and gastric, pancreatic, and biliary secretions. Dietary intake actually constitutes a small portion of the jejunal load (1.5 L). A healthy small intestine absorbs nearly 75% of the fluid to which it is exposed. The 2 L of fluid not absorbed by the small intestine then enters the colon, where fluid is absorbed at an even higher rate. The absorptive power of the colon approaches 90% efficiency and far exceeds that of the small intestine. In fact, the colon can make up for a decrease in small intestinal absorption. Under normal conditions, very little fluid (<100 mL) is lost in the stool each day.4

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In diarrheal states, normal intestinal physiology is disrupted. At a cellular level, intestinal absorption occurs through the villi, and secretion occurs through the crypts. Fluids are absorbed passively with the transport of sodium, and actively with the absorption of glucose. Selected enterotoxins block the passive sodium resorption and specifically stimulate sodium excretion, resulting in a net loss of fluid. The glucose-dependent mechanism of water absorption, however, is unaffected by these toxins and can be exploited by including glucose in the rehydration treatments. The composition of ...

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