Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

278 Small Animal Radiolo g y and Ultrasono graphy
the expense of a contrast study. Even if noncontrast radiographs were obtained several
hours or a day before, they should be repeated. The most commonly performed special
study of the GI tract is the upper GI series using barium. This is indicated when the animal
has exhibited clinical signs of GI disease that have failed to respond to symptomatic
treatment or has other findings (e.g., history of ingestion of foreign matter, suspicious
findings on palpation of the abdomen) that suggest that anatomical evaluation of the GI
tract may be helpful in elucidating the problem. Diarrhea with no other GI sign is rarely
an indication to perform a GI series. The most common mistakes made when performing
a GI contrast study are improper patient preparation, administering too little contrast, and
obtaining too few radiographs after contrast administration. The patient’s GI tract should
be empty before contrast administration, because food and fecal material can mimic or
obscure lesions. This is achieved by withholding all food for at least 12 hours and using
laxatives or enemas or both. If necessary, dogs may be sedated with an intravenous dose
of 0.1 to 3.0 mg of acepromazine unless contraindicated by other factors (e.g., a history of
seizures). 12,81 Cats may be sedated by the intravenous injection of 10 mg of ketamine or by
intramuscular injection of ketamine (10 mg/lb), acepromazine and ketamine (0.1 mg/lb,
6 mg/lb), or ketamine and diazepam (6 mg/lb, 0.2 mg/lb). 82,83 It is important to understand
the effects of various sedatives on the GI tract and how they will affect the upper GI
series. 84-88 A 25% to 40% weight-to-volume suspension of barium is administered by orogastric
or nasogastric intubation at a dosage of 5 to 8 ml/lb. We do not recommend the
routine use of iodine-containing, water-soluble contrast medium for this purpose.
Although others have recommended smaller dosages, it is our experience that the most
common problem with this study is the use of an inadequate dose, which fails to distend
the GI tract completely. Commercially premixed products are preferred to barium powder
that requires mixing with water, because the suspending agents in commercially prepared
products seem to produce superior mucosal detail, more uniform passage, less artifactual
aggregation and flocculation, and a more stable suspension. Both ionic and nonionic
water-soluble iodine-containing contrast media are used by some veterinarians, because
they will pass more rapidly through the GI tract. 12,89,90 The presumed advantage of more
rapid transit by the water-soluble, iodine-containing contrast medium is far outweighed
by the disadvantage of the very poor contrast and detail these products provide, as well as
the risk of pulmonary fluid shifts induced by aspirated hyperosmolar compounds. 12,91,92
These agents do not coat the mucosa very well, and the ionic agents may also irritate the
gastric mucosa and cause vomiting. Furthermore, as the contrast medium passes through
the intestine, the hyperosmolar ionic agents draw body fluids into the intestine. This
results in a decreasing density throughout the study and systemic dehydration, which may
be dangerous in an already dehydrated patient. The use of water-soluble agents has been
recommended when bowel rupture is suspected because of the potential for granulomatous
peritonitis caused by free barium in the abdominal cavity. Although this is a valid
consideration, the possibility of misdiagnosis because of poor contrast density in cases of
minimal leakage from small defects in the bowel, coupled with the opportunity to flush
any leaked barium from the abdomen at laparotomy, leads us to recommend the use of
barium for almost all studies.
Instillation by stomach tube requires certainty that the tube is positioned in the stomach.
Careful palpation of the esophagus after placing the stomach tube is required. Even in
cats, the orogastric tube can be palpated to distinguish it from the trachea if care is exercised.
Use of a stomach tube is superior to oral instillation, because it is common for animals
to expectorate a portion of the barium as well as to inhale some of the barium if they
struggle. They also tend to swallow large amounts of air at the same time. Gastric intubation
ensures that the stomach will receive a proper dose of barium so that it is adequately
distended.
It has been reported that the normal time for barium to reach the colon after instillation
is 90 to 270 minutes in the dog and 30 to 60 minutes in the cat. 81,83,93-98 In dogs,
radiographs should be taken immediately after the barium has been administered and at
intervals of 15 minutes, 30 minutes, 1 hour, 2 hours, 3 hours, and periodically thereafter
until the barium reaches the colon. In the cat, barium passes through the normal
GI tract more rapidly, and therefore radiographs should be taken immediately, and after