Acute gastroenteritis
BackgroundGastroenteritis is a nonspecific term for various pathologic states of the gastrointestinal tract. The primary manifestation is diarrhea, but it may be accompanied by nausea, vomiting, and abdominal painAcute diarrhea means increase in frequency, volume and fluidity of stool less than 14 days duration.Diarrhea associated with nausea and vomiting is referred to as gastroenteritis.
Pathophysiology
Infectious agents usually cause acute gastroenteritis. These agents cause diarrhea by adherence, mucosal invasion, enterotoxin production, and/or cytotoxin production.
These mechanisms result in increased fluid secretion and/or decreased absorption. This produces an increased luminal fluid content that cannot be adequately reabsorbed, leading to dehydration and the loss of electrolytes and nutrients.
Diarrheal illnesses may be classified as follows:
Osmotic: due to an increase in the osmotic load presented to the intestinal lumen, either through excessive intake or diminished absorption
Inflammatory (or mucosal): when the mucosal lining of the intestine is inflamed
Secretory: when increased secretory activity occurs
Motile: caused by intestinal motility disorders
The exact mechanism of vomiting in acute diarrheal illness is not known, although serotonin release has been postulated as a cause, stimulating visceral afferent input to the chemoreceptor trigger zone in the lower brainstem. Preformed neurotoxins produced by Staphylococcus aureus and Bacillus cereus, when ingested, can cause severe vomiting.
Clinical
HistoryDuration of illness
Duration and rapidity of symptom onset are important in determining the incubation period and possible infecting organism and in directing further care.
Diarrhea that lasts longer than a month requires consideration of a different spectrum of etiologic factors than diarrhea that lasts less than 1-2 weeks.
Fever: The presence of fever (with or without chills) generally suggests that an invasive organism is the cause of diarrhea, although many extraintestinal illnesses can present with both fever and diarrhea, especially in children.
Vomiting
Vomiting, a symptom common to a host of illnesses, implies proximal bowel involvement, especially with preformed neurotoxin, as elaborated by S aureus and B cereus.
Pain
The location and character of pain may be indicative of the area of infection because colonic involvement is usually associated with tenesmus and pain in either of the lower quadrants or the lower back, whereas jejunoileal infection may result in periumbilical pain.
Stools
Ask about frequency, nature (amount, color, watery, semisolid, odor), and presence of blood and/or mucus.
Large volumes of stool are usually associated with enteric infection, whereas colonic infection results in many small stools.
The presence of blood indicates colonic ulceration (bacterial infection, inflammatory disease, ischemia).
White bulky feces that float (high fat content) are due to a small bowel pathology that leads to malabsorption.
Copious (rice water) diarrhea is a hallmark of cholera.
Extraintestinal causes (paraenteral diarrhea)
A history of other nonintestinal illnesses that can lead to diarrhea may be obtained. Vomiting and/or diarrhea may be a manifestation of that illness or a result of its treatment. Obtaining a history of recent surgery or radiation, food or drug allergies, and endocrine or gastrointestinal disorders is extremely important. The patient should always be questioned regarding prior episodes.
Dehydration
Orthostasis, lightheadedness, diminished urine formation, and a change in mentation herald marked dehydration and electrolyte loss, requiring aggressive treatment.
These symptoms are particularly important in elderly patients, a group that is most at risk from diarrhea.
Physical
A thorough physical examination is essential to assess the general state of hydration and nutrition and to exclude extraintestinal causes of diarrhea. Often, the cause of diarrhea cannot be determined based on the physical findings present, which may be scarce.
The most important element of the physical examination is the assessment of the patient's hydration status. (Dehydration in children, for example, is classified according to the degree of hydration/percentage deficit as <3%, none; 3-6%, mild; 6-9%, moderate; and >10%, severe.) Additionally, signs of bacteremia or sepsis should be sought. Patients with chronic diarrhea may need an evaluation of their nutritional status.
Hydration and nutritional status
Diminished skin turgor, weight loss, resting hypotension and tachycardia, dry mucus membranes, decreased frequency of urination, changes in mental status, and orthostasis can be used to gauge dehydration.
In children, the absence of tears, poor capillary refill, sunken eyes, depressed fontanelles, increased axillary skin folds, and dry diapers all may reflect a dehydrated state.
Muscle wasting and signs of neural dysfunction due to nutritional depletion may be observed in patients with chronic diarrhea.
Abdominal examination
A careful abdominal examination is necessary to exclude causes of diarrhea that may require surgical intervention, such as pelvic abscesses close to the rectosigmoid that are causing tenesmus.
Causes
Viral (50-70%)
Norovirus
Caliciviruses (Various caliciviruses, other than norovirus, are likely responsible for many outbreaks of previously unidentified viral gastroenteritis.)
HYPERLINK "http://emedicine.medscape.com/article/803885-overview" Rotavirus (This is the leading cause of gastroenteritis in children, but rotavirus can also be found in adults. Rotavirus may cause severe dehydration.)
HYPERLINK "http://emedicine.medscape.com/article/211738-overview" Adenovirus
HYPERLINK "http://emedicine.medscape.com/article/961063-overview" Parvovirus
Bacterial (15-20%)
HYPERLINK "http://emedicine.medscape.com/article/182767-overview" Shigella
HYPERLINK "http://emedicine.medscape.com/article/785774-overview" Salmonella
HYPERLINK "http://emedicine.medscape.com/article/213720-overview" C jejuni
HYPERLINK "http://emedicine.medscape.com/article/232343-overview" Yersinia enterocolitica
HYPERLINK "http://emedicine.medscape.com/article/217485-overview" E coli - Enterohemorrhagic O157:H7, enterotoxigenic, enteroadherent, enteroinvasive
HYPERLINK "http://emedicine.medscape.com/article/232038-overview" V cholera
Parasitic (10-15%)
HYPERLINK "http://emedicine.medscape.com/article/782818-overview" Giardia
HYPERLINK "http://emedicine.medscape.com/article/212029-overview" Amebiasis
HYPERLINK "http://emedicine.medscape.com/article/215490-overview" Cryptosporidium
HYPERLINK "http://emedicine.medscape.com/article/236105-overview" Cyclospora
Food-borne toxigenic diarrhea
Preformed toxin -S aureus, B cereus
Postcolonization -V cholera, C perfringens, enterotoxigenic E coli, Aeromonas
Drug-associated diarrhea
Antibiotics, due to alteration of normal flora
Laxatives, including magnesium-containing antacids
Colchicine
Quinidine
Cholinergics
Sorbitol
Workup
Laboratory Studies
Stool studies and culture
The presence of blood or leukocytes in stool is a strong indicator of inflammatory diarrhea.
Fecal leukocytes are present in 80-90% of all patients with Salmonella or Shigella infections but are less common with other infecting organisms such as Campylobacter and Yersinia.
A stool culture is not necessary or cost-effective in all cases of diarrhea unless a bacterial cause is suspected.
Fever, bloody stools, leukocytes in stool, pain resembling that associated with appendicitis (Yersinia), and diarrheal illness associated with partially cooked hamburger (cytotoxigenic E coli O157:H7) are all indications for culture.
Testing for other pathogens, such as Vibrio species, enterohemorrhagic E coli O157:H7, and other Shigatoxin-producing bacteria require special media.
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INCLUDEPICTURE "http://img.medscape.com/pi/emed/ckb/emergency_medicine/756148-775277-316.jpg" \* MERGEFORMATINET
The MacConkey medium is commonly used and differentiates lactose fermenters, which produce acid, decrease the pH, and cause the neutral red indicator to give the colonies a pink-to-red color.
Routine laboratory tests
Routine laboratory tests (CBC, electrolytes, renal function) may not be helpful or indicated in making a diagnosis. These tests may be useful as indicators of severity of disease, especially in elderly or very young patients, although that determination is best made clinically.
Electrolytes and BUN tests are indicated in patients with severe diarrhea or dehydration to rule out hyponatremia or hypernatremia. Decreased serum bicarbonate suggests severe dehydration, especially in children. Acidosis secondary to bicarbonate loss in the stools and/or from hypovolemia-induced lactic acidosis may be present. Hypokalemia may also occur.
Enzyme-linked immunosorbent assay
Commercially available immunofluorescent antibody and enzyme immunoassays are also available for Giardia and Cryptosporidium organisms. C difficile toxin assays can be performed when antibiotic-associated diarrhea is suspected.
Rotavirus: Enzyme-linked immunosorbent assay (ELISA) is available in less than 2 hours but is not sensitive enough in adults.
Giardia: ELISA is more than 90% sensitive in susceptible populations (eg, people who camp or travel to endemic areas). Consider ELISA prior to ova and parasite examination or string test.
Treatment
Rehydration
Administration of 1-2 L dextrose 5% in 0.5 isotonic sodium chloride solution with 50 mEq NaHCO3 and 10-20 mEq KCl over 30-45 minutes may be necessary in patients who are severely dehydrated.
To give fluids more rapidly, KCl may be given orally or in the second or third liter bag or as a supplemental IV of 20 mEq KCl in 100 mL of isotonic sodium chloride solution over 1 hour.
Rehydrate patients until mental status and signs of perfusion and pulse are normal (caution in elderly patients with congestive heart failure [CHF]).
For pediatric patients, administer 20 mL/kg of isotonic sodium chloride solution initially for resuscitation. Repeat as necessary and add KCl as indicated.
Indications for IV rehydration include severe intractable vomiting, altered consciousness, severe dehydration, ileus, excessive choleralike stools, and time or environment not conducive to oral rehydration therapy (ORT).
Solutions for oral rehydration
The World Health Organization solution is 90 mEq/L Na+, 20 mEq/L K+, 80 mEq/L Cl-, 20 g/L glucose; osmolarity is 310; CHO:Na = 1.2:1; administer 250 mL (approximately 8 oz) every 15 minutes until fluid balance is clinically restored, then 1.5 L of oral fluid per liter of stool.
Oral rehydration has been largely responsible for the tremendous decrease in the death rate in underdeveloped countries from infectious diarrhea, including cholera.
The glucose/sodium transport mechanism remains intact despite enterotoxigenic illness. Coupled transport is one of several mechanisms of sodium and water absorption in the bowel. It is the direct entry of sodium and water across the cell at the intestinal brush border membrane via the linking (coupling) of 1 organic molecule, such as glucose, to 1 sodium molecule. This is the principle upon which ORT is based. Optimally, therefore, the ratio of carbohydrate to sodium should approach 1:1. Glucose is necessary to stimulate the absorption of water and electrolytes by the small intestines.
The solution must be iso-osmolar or hypo-osmolar to avoid an increased osmotic load in the small intestines contributing to an osmotic diarrheal effect, pulling fluid into the lumen.
Studies have shown oral and IV rehydration to be equivalent therapies in patients who can tolerate the oral fluid.
Although standard glucose-electrolyte solutions achieve and maintain rehydration, they may not reduce stool volume or duration of diarrheal illness, affecting compliance.
Newer solutions with complex carbohydrates and short chain polypeptides of cereals and legumes are now available to provide additional organic cotransport molecules with no increase in osmolarity. These appear to offer the advantage of decreased stool volumes and shortened duration of illness.
Early age-appropriate refeeding in children (and adults) is important to initiate as soon as rehydration is complete.
Empiric therapy for infectious diarrhea is sometimes indicated. Food-borne toxigenic diarrhea usually requires only supportive treatment, not antibiotics.
Mild cases of suspected Yersinia infection should be treated with TMP/SMZ or a fluoroquinolone, while patients who are more ill and require admission benefit from IV ceftriaxone.
Intestinal salmonellosis in an immunocompetent host does not require antimicrobials because they may prolong fecal shedding of organisms.
Metronidazole is effective against parasitic infestations with Giardia or Entamoeba.
Antiemetics may be useful in the treatment of nausea and vomiting in adults. They are usually not recommended in children.
Antidiarrheals (antimotility agents)
These agents have traditionally been discouraged because of concerns with causing bacteremia; however, they appear to have a role in the symptomatic treatment of mild-to-moderate diarrhea, especially with nonbloody and traveler's diarrhea.
IDEAL GROUP
A.H.M.Yahia