Diagnostic evaluation of vomiting
2.1.2.1 Vomiting versus regurgitation
It is critical to distinguish between vomiting, regurgitation, and gastroesophageal reflux when obtaining the initial history, because the diagnostic and treatment approaches are vastly different.
Vomiting is a reflex act that includes prodromal signs followed by active abdominal contractions.1 The prodromal signs may include behavioral changes, salivation, and repeated swallowing attempts.1 It must be emphasized that these signs are variable. In contrast, regurgitation is a passive act that is often spontaneous or associated with changes in body position. There are no prodromal signs and there are no repetitive abdominal contractions. Regurgitation is typically associated with disorders of the esophagus (see 3.3). The best way to differentiate these two clinical signs is to imitate the two acts for the client, emphasizing the repetitive abdominal contractions seen in the vomiting patient as the most reliable distinguishing feature. The timing of the event with respect to eating, the volume of material brought up, or the character of the contents (unless it contains bile, suggestive of vomiting) do not reliably distinguish vomiting from regurgitation.2.1.2.2 Thevomitingreflex
The vomiting reflex begins with afferent receptors located in visceral organs (including GI tract, pancreas, heart, liver, genitourinary tract, and peritoneum) and the pharynx.1 The afferent impulses travel through the vagus and sympathetic nerves to the vomiting center located in the medulla. Vomiting can also be initiated by stimulation of the chemoreceptor trigger zone (CRTZ) located in the area postrema of the medulla.1 The CRTZ is sensitive to blood-borne substances. The vomiting reflex can also be initiated by input from the cerebral cortex (rare in animals vs.
human beings) and from the vestibular apparatus (i.e., motion sickness). Thus, vomiting can be initiated through a “humoral” pathway, caused by blood-borne substances stimulating the CRTZ, or a “neural” pathway, caused by stimulation of the vomiting center from vagosympathetic, CRTZ, vestibular, or cerebral neurons. Examples of vomiting caused by activation of the humoral pathway include chemotherapy drugs, digitalis, uremic toxins, and apomorphine. Examples of vomiting caused by activation of the neural pathway include gastroenteritis, pancreatitis, peritonitis, motion sickness, and emotions (cerebral input). It has also been suggested that vomiting can be initiated by both of these pathways simultaneously.1 Knowledge of the cause of the vomiting will also aid the clinician in selecting the most appropriate antiemetic drug.2.1.2.3 Etiology of vomiting
Acute vomiting can be caused by numerous disorders. These can be divided into gastrointestinal disorders and extra-gastrointestinal disorders (Table 2.1). It is beyond the scope of this chapter to discuss in detail the clinical findings and treatment of each disorder, however, many of these are discussed in other sections of this book.
2.1.2.4 History and physical examination
As mentioned above, it is critical to distinguish vomiting from regurgitation. In addition, there are several other historical features that help the clinician either determine the cause or direct the diagnostic workup. The client should be questioned for any
| Table 2.1: Etiology of acute vomiting | |
| Gastrointestinal Causes | Extra-Gastrointestinal Causes |
| Inflammatory ■ Inflammatory bowel disease (IBD) | Hepatobiliary disorders |
| ■ Infectious (viral, bacterial, parasitic) ■ Hemorrhagic gastroenteritis (HGE) | Renal disorders |
| ■ Nonspecific (“garbage can intoxication") | Endocrine disorders |
| ■ Ulcer | ■ Hypoadrenocorticism ■ Feline hyperthyroidism |
| Drugs and toxins | ■ Diabetic ketoacidosis |
| Mechanical | Exocrine pancreatic disease |
| ■ Foreign body ■ Gastric dilation-volvulus | ■ Acute pancreatitis |
| ■ Intestinalvolvulus | Reproductive disorders |
| ■ Intussusception | ■ Pyometra |
| ■ Neoplasia | ■ Prostatitis |
| ■ Pyloric stenosis Functional | ■ Testiculartorsion ■ Orchitis |
| ■ Primary motility disorders | Miscellaneous disorders |
| ■ Motility disorders secondary to GI inflammation or peritonitis | ■ CNSdisorders ■ Drugs ■ Toxins |
previous illness that could relate to the current problem. There should be a complete history including the current diet (or any dietary changes), vaccination and deworming status, onset of clinical signs, other systemic signs, exposure to drugs, toxins, or garbage, and exposure to foreign objects.
The history should also help determine the severity of the clinical signs, and should therefore include the severity and frequency of vomiting, and the appearance of the vomitus. The presence of anorexia, profuse vomiting and hematemesis often warrant a more intense diagnostic and treatment plan. The physical examination should be thorough for all organ systems, and include careful abdominal palpation, an examination under the tongue for a possible string foreign body, and careful rectal palpation. The physical examination should also help determine the severity of the patient’s illness. Features that suggest that more aggressive supportive care will be required include weakness, dehydration, severe depression, fever, abdominal distension, severe abdominal pain, an abdominal mass, and findings suggestive of shock. These findings also warrant laboratory and ancillary testing to determine a specific diagnosis if possible, and to assess metabolic consequences such as electrolyte and acid-base disturbances. It must be recognized early whether there are disorders that require immediate medical intervention (such as severe viral enteritis) or surgical intervention (such as gastric dilation / volvulus or a small intestinal obstruction).2.1.2.5 Laboratory and ancillary testing
The thoroughness of laboratory and ancillary testing will depend on the severity of the problem, as determined by the factors described above. The minimum data base should include a complete blood count (CBC), serum biochemistry profile, and urinalysis. These data would screen for some of the extra-gastrointestinal causes of vomiting, help assess electrolyte abnormalities, and screen for an abnormal leukogram that may suggest a viral or inflammatory disorder. Endocrine testing may be warranted, including a serum total T4 concentration in cats, and possibly an ACTH stimulation test in dogs that are suspected of having hypoadrenocorticism. Abdominal radiographs are warranted to look for mechanical causes of vomiting, including gastric dilation/volvulus, gastrointestinal foreign body, and small intestinal obstruction.
If these disorders are suspected based on plain radiographs, one could proceed directly to surgery. The features of an intestinal obstruction have been described elsewhere, and include most commonly dilated gas- and fluid-filled bowel loops.2 In some instances, it cannot be determined whether a dilated gas-filled loop of bowel is small bowel (suggesting an obstruction) or large bowel (typically normal). An inexpensive easy test to distinguish large bowel gas from small bowel gas is a pneumocolon- ogram. This is performed by placing a Foley catheter (or large red rubber catheter) into the rectum and slowly infusing 20 ml/kg of room air. Lateral and ventrodorsal radiographs areobtained immediately. If the dilated loops of bowel in question are small intestinal in origin, they will remain separate from the dilated air-filled colon. If the dilated loops of bowel in question are large intestinal in origin, they will disappear and “blend” in with the dilated air-filled colon. In some instances, an upper gastrointestinal barium series is necessary to determine if an obstruction is present. It is important that the proper amount of barium is administered (10-12 ml/kg).3 Iodinated contrast is given if there is suspected gastrointestinal perforation or if endoscopy may be performed with contrast material in the stomach. Endoscopy is generally only warranted in the evaluation of acute vomiting if there is a suspected gastric or duodenal foreign body, or possible ulceration in these regions. Abdominal ultrasonography may be helpful in certain instances, including screening of organs outside of the gastrointestinal tract. The liver, biliary system, kidney, reproductive tract, and pancreas can be examined by transabdominal ultrasonography. Gastrointestinal disorders that can be evaluated by ultrasonography include intussusception, small intestinal obstruction due to neoplasia or foreign body, peritonitis, and pancreatitis. Finally, specific laboratory testing for specific diseases may be warranted. Serum pancreatic lipase immunoreactivity is helpful in the diagnosis of pancreatitis (see 1.4.4.2). Infectious disease testing may include specific fecal cultures for Salmonella spp., Campylobacter spp., and Yersinia spp., testing for fecal enterotoxins from Clostridium spp., and specific fecal antigen testing for canine parvovirus, Giardia spp., or Cryptosporidium parvum.
2.1.3