Small Animal – Gastroenterology
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MANAGING THE VOMITING DOG of the glossopharyngeal nerve. Central nervous system
(CNS) disease may directly stimulate the vomiting center
David C. Twedt, DVM, Diplomate ACVIM such as direct extension of inflammatory stimuli,
Colorado State University hydrocephalus or space occupying lesions. Cyclic
Fort Collins, CO vomiting in the dog has been associated with autonomic
or visceral epilepsy arising from the limbic region.
Vomiting is a common clinical sign in small animals. The vomiting center is stimulated indirectly via a
Although vomiting is a protective mechanism developed humoral or blood-borne factors by activating the
to remove ingested noxious substances it also is chemoreceptor trigger zone (CRTZ) located in the area
associated with many disease conditions including those postrema. The blood–brain barrier is limited in this area
of the gastrointestinal system, other abdominal that allows the CRTZ to be exposed to chemical stimuli
conditions, systemic or metabolic disease and drug found in the circulation. Blood-borne substances
toxicity, to name a few (Table 1). Severe vomiting can stimulating the CRTZ include certain drugs, uremic
result also in serious consequences including volume toxins, electrolyte, osmolar and acid–base disorders as
depletion, acid-base and electrolyte disturbance, well as a number of metabolic derangements. Drugs
esophagitis, aspiration pneumonia, and malnutrition. An such as apomorphine or cardiac glycosides and bacterial
overview of the pathophysiology, potential etiologies, toxins are examples. There is also evidence in the dog
antiemetic therapy and a logical clinical approach to the that vestibular stimulation passes through the CRTZ
chronic vomiting patient are presented in this article. before activating the vomiting center. Motion sickness,
The act of vomiting is divided into three components; inflammation of the labyrinth, or lesions in the
nausea, retching, and vomiting. Nausea precedes cerebellum result in vomiting via this pathway.
retching and is associated with salivation and
swallowing. This is followed by motility changes in the GI ANTIEMETICS: THEIR SELECTION AND USE
tract with relaxation of the stomach and lower Antiemetics are drugs used to control nausea and
esophageal sphincter. Retching results from the forceful vomiting. When selecting an antiemetic for a vomiting
contractions of the abdominal muscles and diaphragm. patient it is important to have an idea as to the probable
Vomiting then occurs as gastric contents are forcefully etiology so an appropriate class of antiemetic can be
expelled out of the mouth. The driving force is selected for the specific causes in each individual case.
contraction of the abdominal muscles and diaphragm Antimetics should be used because they aid in
causing intrathoracic pressure changes from negative controlling the nausea and vomiting, make the patient
during retching to positive during vomiting. more comfortable, and may actually return them back to
Although vomiting is a complex and poorly earlier state of positive nutrition. Antiemetics are also
understood event it is simply best described as a reflex indicated when there is serious fluid and electrolyte loss
act that is initiated by stimulation of the conceptualized with dehydration or from the fear of aspiration
“vomiting or emetic center” located in the medulla pneumonia. Antimetics should not be used if the patient
oblongata of the brain. Activation of the vomiting center has a GI obstruction in which surgery would be indicated
occurs either through a humoral pathway initiated via or if the side effects of the antiemetic would
blood-borne substances or by activation through various contraindicate their use. There are some that believe
neural pathways leading to the vomiting center. It is also antiemetics should not be used in the management of
sometimes also classified as either centrally mediated vomiting because they may mask the signs, therefore
(from CNS mediation) or peripherally mediated (from providing a false sense of security of clinical
distant structures in the abdominal cavity). improvement and may consequently making the correct
Understanding this concept helps one formulate a diagnosis. I believe this paradigm is shifting and now it is
differential list of etiologies. felt that antiemetics actually make the patient more
Neural stimulation of the vomiting center arises comfortable. Antiemetic therapy, however, should not be
through either afferent vagal, sympathetic, vestibular, an excuse for an accurate diagnostic workup.
and cerebrocortical pathways. Activation of peripheral Common antiemetic agents used in small animal
receptors found throughout the body can stimulate these verterinary medicine, the receptors they block, and their
neural pathways. Particularly important are receptors anatomic location and potential side effects are listed in
that are located throughout the abdominal viscera but Table 1.
especially those located in the duodenum, which A newer antiemetic recently approved for used in
contains the highest concentration and hence has been dogs is maropitant (Cerenia™). This is an NK1
referred to as the “organ of nausea.” Disease or irritation antagonist that works in blocking vestibular, CRTZ,
of the gastrointestinal tract, other abdominal organs, or emetic center and peripherial input. I used this broad-
peritoneum can directly stimulate vomiting through vagal spectrum antiemetic in a preliminary pre-launch trial of
afferent pathways. Receptors in the kidneys, uterus, and 50 vomiting cases. The drug was effective in controlling
urinary bladder send afferent impulses via sympathetic vomiting in most every case with virtually no side effects.
nerves while receptors located in the pharynx and This drug can be given subcutaneously (SQ) or orally
tonsilar fossae transmit impulses thorough afferent fibers once daily.
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NAVC Conference 2008
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Table 1. Common Causes of Vomiting
Metabolic/Endocrine Dietary Large Intestinal Disorders
Disorders Indiscretions Colitis
Uremia Intolerances Obstipation
Hypoadrenocorticism Allergy Parasites
Diabetes mellitus
Hyperthyroidism Gastric Disorders Abdominal Disorders
Hepatic disease Gastritis Pancreatitis
Endotoxemia/septicemia Helicobacter Peritonitis
Hepatic encephalopathy Parasites Neoplasia
Electrolyte disorders Ulceration Hepatobilary disease
Acid-base disorders Neoplasia
Foreign bodies
Intoxicants Dilatation-volvulus
Lead Hiatal hernia
Ethylene glycol Obstruction
Zinc Motility disorders
Strichnine
Small Intestinal Disorders
Drugs Inflammatory bowel disease
Cardiac glycosides Neoplasia
Erythromycin Foreign body
Chemotherapy agents Intussusception
Apomorphine Parasites
Xylazine Parvovirus
Penicillamine Bacterial overgrowth
Tetracycline
NSAIDs
Table 2. Antiemetic Agents Used in Small Animal Veterinary Medicine
Drug Mode of Action Location of Action
Antihistamines Block cholinergic and Vestibular, CRTZ
histaminergic
receptors
Phenothiazines Alpha-2 antagonists Emetic center, CRTZ
Propantheline, Anticholinergic CRTZ, peripherial
isopropamide
Metoclopramide Antidopaminergic CRTZ
Ondansetron, Serotonin (5HT3) Emetic center, CRTZ,
dolasetron antagonists peripherial
Maropitant Neurokinin-1 (NK-1) Emetic center, CRTZ,
(Cerenia™) antagonists peripherial
CLINICAL APPROACH
When dealing with the vomiting patient there are four regurgitation which the client may confuse with vomiting.
important things to determine in the history: 1) is the In some cases, this may be difficult to differentiate based
patient actually vomiting, 2) a detailed vomiting history, on the history alone.
3) drug and diet history, and 4) other signs or symptoms The signalment may also be helpful for example,
associated with the vomiting. The history should confirm young unvaccinated patients are more susceptible to
the patient is truly vomiting and that the signs described infectious disease such as parvovirus or distemper while
are not associated with gagging, coughing, dysphagia or an older animals generally would bring about a different
set of differentials. Vaccination status, travel history,
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Small Animal – Gastroenterology
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previous medical problems, as well as medication history are identified the chronic vomiting patient should next be
should be determined. In particular it should be noted if classified as either having mild disease with minimal
nonsteroidal anti-inflammatory drugs (NSAIDs) have debilitation or those having a significant history with
been used. Questions should also investigate concurrent serious debilitation. Those patients having significant or
signs that may occur with systemic or metabolic disease. serious disease will require an in-depth diagnostic
For example, polydipsia, polyuria, and weight loss are workup with emphasis on the gastrointestinal tract
typical for vomiting associated with diabetic ketoacidosis including contrast studies, ultrasound examination, and
or chronic renal failure. endoscopy. Animals that fail to respond to symptomatic
The history should then focus on the actual vomiting therapy will also require in-depth diagnostic workup.
episodes. As in the old television series Dragnet when Animals with mild signs and minimal debilitation
Friday says “ D’facts madam give me only D’facts,” should first have dietary manipulation with food trials and
D’FACTs one should obtain are: D) duration, F) treatment for gastrointestinal parasites. These
frequency, A) association with eating or drinking, C) therapeutic trials are very appropriate in this
character of the vomitus and T) treatments that have classification of cases. Adverse reactions to food
been given for the vomiting. A dietary history including consists of either food allergies or food intolerances.
the type of diet or recent diet change is equally important Intolerances refer to direct reactions to a specific
because vomiting may be associated with an adverse substance in the diet such as a preservative or dye while
reaction to food. Vomiting in the immediate postprandial an allergy is a specific immunologic reaction mediated
period may suggest an adverse reaction to food or against a protein antigen. Both can result in variable
possibly simply overeating. Vomiting undigested or a inflammatory gastric mucosal changes and vomiting.
partially digested meal, especially when it is greater than Dietary food intolerances are probably the most common
6 to 8 hours following eating, a point at which the cause of chronic intermittent vomiting. Most animals
stomach should normally be empty, suggests a gastric appear healthy and have only intermittent vomiting,
outflow obstruction or a primary gastric hypomotility primarily food, shortly following eating. Removal of the
disorder. Gastric outflow obstructions occur from foreign agent often results in prompt improvement. Food
bodies, mucosal hypertrophy, tumors or polyps. Vomiting allergies are the result of a reaction to a specific protein
of a bile-tinged fluid, especially in the early morning antigen, usually the major antigen in the diet.
hours often results from enterogastric reflux syndrome. Animals suspected of having food related reactions
The presence of blood in the vomitus either as fresh should be placed on a hypoallergenic diet for at least a
“bright red” blood or digested blood that has a “coffee 2-week trial. Although food allergies causing
grounds” appearance indicates gastrointestinal erosion dermatologic signs may take prolonged diet trials for a
or ulceration. Hematemesis with metabolic-related ulcers response to occur GI-related signs tend to respond
such as hypoadrenocorticism or uremia, drug-induced within several weeks. There is no universal ideal diet
ulceration, gastritis, or gastric neoplasia are possible and various dietary trials may be required. If the patient
etiologies. is dietary responsive that supports the diagnosis.
A complete physical examination may provide Parasites must always be considered when dealing
important information. Careful evaluation for other with chronic vomiting in animals with little debilitation.
abnormalities can be a clue to the etiology of vomiting. Giardia, ascarids, and whipworms are usually diagnosed
The abdomen should be carefully palpated for bowel using proper fecal examination techniques. Physaloptera
distention, effusion, masses or organomegaly. A rectal infection in dogs is uncommon but may be
examination provides characteristics of colonic mucosa underestimated due to difficulty of diagnosis. Prevalence
and feces. Melena suggests upper gastrointestinal rates in the United States range from 1% to 25%. The
bleeding and the presence of foreign material in the worm burden need not be large to cause clinical signs. It
feces helps support a foreign body etiology. Patients is not unusual to find only one or two worms causing
having colitis or the severely obstipated animal will also significant clinical signs include chronic intermittent
often vomit. vomiting. The adults produce few eggs and because the
eggs are larvated, they may not float during routine fecal
DIAGNOSTIC PLAN flotation. The diagnosis is most frequently made during
The history, physical examination, and basic endoscopy by simply viewing the parasite in the stomach
laboratory findings should direct the clinician to a or proximal duodenum. When symptomatic therapy is
diagnosis or the next step in the workup. Most cases of indicated with the chronic vomiting case anthelmintic trial
acute vomiting are associated with a “garbage gut”; in therapy will rule out parasites as a cause. I usually
these cases, little to no diagnostics are required and a prescribe febendazole at 50 mg/kg daily for 3 to 5 days.
response to symptomatic therapy confirms the An in depth GI evaluation should be considered in
diagnosis. In severe cases or those that have chronic the vomiting animal with significant or severe gastric or
vomiting, laboratory diagnostics are indicated and should gastrointestinal disease or in the patient that has failed
include a minimum data base (complete blood count to respond to adequate dietary and anthelmintic therapy.
[CBC], biochemical profile and urinalysis) fecal Persistent vomiting, hematemesis, weight loss and
examination and abdominal radiographs. This basic debilitation signify further diagnostic evaluation.
evaluation is essential in excluding all non- Diagnostic techniques of the stomach involve radiology,
gastrointestinal causes of vomiting. If no abnormalities ultrasonography, endoscopy and/or surgery. Radiology
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NAVC Conference 2008
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should be performed when a gastric lesion, foreign body, occur alone or in conjunction with inflammatory changes
or outflow obstruction is suspected. My preferred means in bowel. The role of Helicobacter sp in gastric disease is
of evaluating the stomach using contrast radiology is uncertain because the organism is found in many normal
performing a double contrast gastrogram. The technique dogs and cats. However, dogs having Helicobacter and
involves administering barium sulfate suspension (1–2 concurrent gastritis should be treated as such and many
mL/kg) via stomach tube, then rolling the patient to coat will improve. Current recommendations of helicobacter
the mucosa and replacing the stomach tube and include combinations of metronidazole and amoxicillin in
distending the gastric lumen with air. If sedation is combination with an acid blocking drug for 2 to 3 weeks.
required acepromazine should be used as it causes Other antibiotic combinations have also been used as
limited alteration in gastric motility. This technique gives well. Less common mucosal disorders include conditions
good mucosal delineation and identifies intraluminal causing gastric ulcerations, fungal disease, and
foreign bodies or lesions. If no lesion is identified neoplasia.
additional barium can be then given to perform a Conditions causing gastric outflow obstructions most
standard upper gastrointestinal study. often are associated with gastrointestinal foreign bodies
Barium mixed with food appears to be a better test of or neoplasia. Antral-pyloric mucosal hypertrophy is a
gastric emptying for disorders of motility. As a general uncommon condition characterized by hypertrophy of the
rule barium mixed with a standard meal should empty by mucosa in the antral and pyloric region of the stomach
8 to 10 hours. Animals with markedly prolonged that causes obstruction of gastric outflow. It is
emptying time following a barium meal are considered to associated with chronic vomiting of food or gastric
have a gastric motility disorder. secretions. The diagnosis is made by identifying gastric
Endoscopy offers the best means of examining the retention on a barium contrast study with distinct
gastric mucosal surface and lumen and to obtain a mucosal folds in the antral region of the stomach. The
gastric mucosal biopsy. When evaluating the vomiting therapy involves surgery and generally has a good
patient I always obtain duodenal biopsies to rule out prognosis.
inflammatory bowel disease, gastric mucosal brush If inflammatory and obstructive gastric disorders have
cytology for Helicobacter, and obtain a gastric mucosal been eliminated then gastric motility disorders should be
biopsy sample for urea culture for Helicobacter. considered. Most gastric motility disorders result in
If endoscopy is not available then a surgical delayed gastric emptying with gastric retention and
exploratory and full thickness biopsy may be indicated. vomiting. The vomiting may occur at any interval
One should evaluate the entire abdomen taking careful following a meal. The relationship to eating is important
note of the liver, pancreas, and bowel. Full thickness however as the normal stomach should be empty of a
biopsy of the duodenum, jejunum, and ileum in addition meal in approximately 8 to 10 hours. Vomiting of a meal
to the stomach is always performed in patients with greater than 10 hours following eating is suggestive of a
gastrointestinal signs. gastric retention disorder. Animals often respond to
frequent semi-liquid diets and gastric prokinetic agents
GASTRIC DISORDERS such as metoclopramide, cisapride or erythromycin.
If non-gastric causes of vomiting have been A common condition observed in dogs the bilious
eliminated then gastric etiologies should then be vomiting syndrome or reflux gastritis. It is generally
considered. Gastric disorders can be simply grouped associated with early morning vomiting of bile without
into conditions of mucosal involvement, those causing food. It is thought to result from reflux of duodenal fluid
gastric out-flow obstruction, and gastric motility into the gastric lumen thus causing gastric mucosal
disorders. Inflammatory gastric mucosal disorders most irritation. Reflux may in part be associated with abnormal
commonly include lymphocytic-plasmacytic, eosinophilic gastric motility however, duodenal disorders should be
or granulomatous gastritis. These conditions are ruled out first. Most dogs respond to either a late
diagnosed by biopsy. Inflammatory gastric disease may bedtime meal and/or prokinetic agents.
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