Identify the Problem
It is important to differentiate vomiting from regurgitation which involves the retrograde movement of food and fluid from the oesophagus, pharynx and oral cavity without initiation of reflex neural pathways other than the gag reflex.
It is also important to differentiate vomiting from coughing followed by gagging which is often confused by owners with vomiting.
Owners are often unable to differentiate vomiting, regurgitating and gagging and therefore one must ask specific questions to elicit appropriate information, e.g., amount of effort involved, character of vomitus etc. If still uncertain, the veterinarian may need to observe the animal.
Primary vs. Secondary Gastrointestinal Disorders
It is therefore apparent that vomiting may occur due to primary gastrointestinal disease (diseases directly involving the gastrointestinal tract) or from secondary or non-gastrointestinal disease, i.e., abnormalities of other systems that indirectly cause vomiting either due to the action of toxins on the CRTZ or by stimulation of peripheral non-GI associated vomiting receptors.
Identify the Body System
It is important to determine whether primary or secondary gastrointestinal disease is occurring as much time and money can be wasted if the wrong system is investigated.
Primary GI Disease
In general (there are always exceptions): In primary upper gastrointestinal disease the vomiting will often (but not always) relate in time to eating e.g., the animal always vomits half an hour after eating. Usually, the shorter the interval between eating and vomiting, the higher up the gastrointestinal tract the lesion is located.
However, vomiting may be delayed for some hours (up to 24 hours) in animals with non-inflammatory gastric disorders. Animals with foreign bodies or secretory disorders of the bowel often vomit despite not eating. Also in lower bowel disorders, vomiting more commonly occurs at variable times after eating.
Animals with primary gastrointestinal disorders may be normal in all respects, including appetite or may be depressed and inappetant due either to the particular lesion e.g., neoplasia or local effects of a foreign body, or to the secondary effects of prolonged vomiting e.g., dehydration, electrolyte disturbances, shock.
When is primary GI disease most likely?
Primary gastrointestinal disease should be strongly suspected if:
An abnormality is palpable in the gut e.g., foreign body, intussusception,
If the vomiting is associated with significant diarrhoea (but remember that primary GI causes of vomiting are frequently not associated with diarrhoea), or
If the animal is clinically and historically normal in all other respects.
Secondary GI Disease
In animals with secondary gastrointestinal disease who are vomiting due to the effect of toxins on the vomiting centre or CRTZ or because of stimulation of non-GI associated peripheral receptors, vomiting tends to be unrelated to eating (except pancreatitis).
They will often have evidence from the history and/or clinical examination of abnormalities affecting other organ systems. Vomiting is usually intermittent, unrelated to eating and may often occur subsequent to the onset of other signs of malaise. In general, animals that are vomiting due to extra gastrointestinal disease are metabolically ill.
The exception to these generalizations is pancreatitis which behaves like a primary GI disease--i.e., acute onset vomiting in an often, otherwise well dog, vomiting immediately after eating, decreased appetite and depression develop and usually do not precede vomiting.
Diagnostic Approach to the Vomiting Patient
Careful evaluation of the history and physical examination findings for any signs that may suggest secondary or primary gastrointestinal disease is imperative.
If indicated by the history and/or physical examination investigate extra gastrointestinal disease with appropriate tests. Only a proportion of vomiting animals will require a diagnostic work up but it is still important to consider whether primary or secondary GI disease is likely.
The most common causes of primary GI disease e.g., gastritis, will respond satisfactorily to symptomatic treatment. However, most secondary GI disease will not and further information is required for management and prognosis.
When is clinical pathology useful?
In general, clinical pathology is most useful in providing information about secondary gastrointestinal diseases causing vomiting. For most primary gastrointestinal disease, clinical pathology tests provide information about the systemic effects of vomiting but not about the aetiology of the disorder.
However, if you are unable to determine from the history and physical examination if the animal has primary or secondary GI disease, it is cheaper, less invasive and usually quicker to investigate secondary GI disease first with appropriate tests then investigate primary GI disease (plain & contrast radiographs, endoscopy, exploratory laparotomy) if clinical pathology is normal.
A fuller work-up (either for diagnosis or to assess the systemic effects of vomiting) vs. symptomatic therapy may be indicated if:
There has been no response to symptomatic therapy
Vomiting is persistent and severe
Other clinical signs are present, e.g., polydipsia, icterus, inappetence (that started prior to the onset of vomiting), severe depression, palpable abnormalities in the gut
Primary Gastrointestinal Disease
Clinical pathology will be of little value in the diagnosis of primary GIT disease and diagnostic procedures such as plain and/or contrast radiographs, exploratory laparotomy or endoscopy should be considered.
When primary GI disease is suspected, diagnostic procedures should be aimed at visualising the gastrointestinal tract
However, it is important to do appropriate tests to assess the patient's hydration and electrolyte/acid base status as prolonged and severe vomiting may cause biochemical derangements such as alkalosis, acidosis, prerenal azotemia, hypokalemia, hyponatremia, and hypochloremia.
Identify the Anatomical Location
If primary gastrointestinal disease is determined to be present, the temporal relationship of vomiting to eating, the character of the vomitus etc. should be used to assess where the lesion is likely to be.
Diagnostic tools such as contrast radiography may be appropriate to localize the lesion. An assessment of the likely location of the lesion is important as this may determine what further diagnostic procedures are suitable. For example, endoscopy would be appropriate for examining the stomach and possibly duodenum but will be of little use if lower small bowel disease is suspected.
Identify the Lesion
Primary GI Disease
Once the lesion has been located (by radiography or visualized in some manner), it must now be identified. Thus biopsy may be appropriate or the type of lesion may be evident by visual inspection (e.g., foreign body).
In the gastrointestinal tract as elsewhere, neoplasia and inflammation often look grossly identical and biopsies should always be taken. Similarly, even if the gastrointestinal tract looks grossly normal, biopsies should be obtained.
Secondary GI Disorders
A large number of secondary gastrointestinal disorders can cause vomiting. However, most of these can be eliminated with relatively few tests. In Table 1 the most important non-gastrointestinal disorders are listed with tests that are useful in diagnosis.
Table 1. Secondary gastrointestinal causes of vomiting in cats and dogs.
Amylase*, lipase*, WBC count, ALP, PLI
ALT, ALP,GGT, bile acids, bilirubin
Urea, creatinine, phosphate, urine SG
Na+, K+, urea, cortisol
Blood and urine glucose, ketones
Toxaemia due to infection
CSF analysis (possibly)
Heartworm antigen tests (often negative), eosinophil count
Blood lead and/or urinary δ-ALA
*Not useful in cats