The patient should be prepared by holding it off food for at least 24–36 hours as animals with gastrointestinal pathology may not empty their stomachs readily. Avoid all prokinetics (e.g., metoclopramide) as they might make it harder to pass the instrument through the pylorus. Also remember that as the stomach is distended with air, it will become harder for the patient to take deep breaths, and one may have to bag the patient to ensure that an adequate plane of anesthesia is maintained.
The basic principles to remember are: Unless there is a good reason to do so, do not extensively reposition the patient (i.e., switch from left lateral to right lateral to dorsal, etc.) during the procedure lest you cause gastric volvulus. If a gastric volvulus occurs because of your manipulations while the patient has a distended stomach, wait and see. These usually spontaneously resolve.
Enteroscopy is primarily performed to obtain intestinal biopsies, although removal of gastric and/or duodenal foreign objects is occasionally indicated. Excessive gastric distention in a large dog may also cause the diameter of the stomach to become so large that you cannot reach the pylorus with the tip of the endoscope. Therefore, in larger dogs it may be best to pass the tip of the scope into the duodenum before examining the stomach. Enteroscopy begins when the tip of the scope passes through the pylorus and into the duodenum. If the pylorus is tightly closed, the tip of the scope must be slowly and carefully forced through the sphincter. When the patient is in left lateral recumbency, the duodenum curves to the right immediately after one enters the pylorus. Gastric mucosa is relatively smooth but small intestinal mucosa will be distinctly textured due to the villi. If there is excessive difficulty in entering the duodenum, you can pass a biopsy instrument through the scope and into the closed pylorus to act as a guide wire. This technique should not be done routinely because it is easy to traumatize the duodenal mucosa and cause bleeding, which may obscure subtle lesions or ulcers (the portion of the duodenum immediately after the pylorus is a common place to find tumors, and this is the area that would be most traumatized by this "guidewire" technique).
The hardest area of the intestinal mucosa to evaluate is that immediately after the pylorus. If an ulcer is present in the pylorus, the pylorus will be thicker than normal due to inflammation, making it harder to pass the scope tip into the duodenum. It may also be difficult to draw the scope tip out through the pylorus slowly so that you can examine the mucosa. Often, there will be no movement of mucosa as you attempt to withdraw the endoscope back out of the pylorus. This paradoxical movement is caused by the increased tone at the pylorus which creates more resistance when the scope moves through the pylorus. Withdraw of the insertion tube from the animal's mouth results first in removing excessive bends of the insertion tube that are within the body of the stomach. When these excess bends are gone, the tip will suddenly "rush" backwards into the body of the stomach (i.e., the "slingshot" effect).
One should avoid biopsying the alimentary tract while it is maximally distended with insufflated air; "thicker" bites of mucosa can be obtained if the organ is somewhat deflated. Always note how difficult it is to biopsy a particular lesion; some infiltrative lesions (i.e., scirrhous carcinomas, pythiosis) characteristically produce so much connective tissue that the flexible biopsy forceps cannot "bite" into the tissue and tear off a piece. Such a finding suggests that surgery and full-thickness biopsy are required. Occasionally, proliferative lesions are deeper than the mucosa so that only normal-appearing mucosa is seen; in such cases repeat biopsies in the same spot are necessary in order to reach the underlying lesion. Biopsying is often best performed when the opened biopsy instrument can be pushed against the mucosa at a near-90° angle.
Intestinal Linear Foreign Objects
When removing linear foreign objects which are trailing off into the duodenum, one should attempt to pass the endoscope through the pylorus so that one can grab the distal end (or at least near the distal end) of the object. The distal end is then pulled into the stomach, meaning that little or none of the object remains in the esophagus. If there is still a little bit of the foreign object in the intestine, it can usually be removed simply by pulling it into the stomach. If the foreign object is relatively thick (e.g., cloth, cotton), as opposed to thin (e.g., twine, string, narrow strips of cloth), one can try to pull it into the stomach simply by grasping it near the pylorus and pulling. However, this approach risks rupturing the duodenum, especially if the foreign object has been present for more than 2–4 days. Therefore, this approach should only be tried with caution.
Flexible colono-ileoscopy is indicated in any animal with signs of large bowel disease (e.g., hematochezia, mucoid stool, diarrhea without weight loss), but especially when rigid colonoscopy and biopsy are nondiagnostic. It is also useful for obtaining ileal biopsies in animals with signs of small intestinal disease (e.g., diarrhea, weight loss, vomiting) and animals with signs of ileal intussusception (e.g., protein-losing enteropathy in young dogs, persistent vomiting/diarrhea after an acute enteritis such as parvovirus, elongated mass in abdomen, sudden onset of scant, bloody stools in a vomiting animal with abdominal pain, sudden deterioration in an animal with prior abdominal surgery/disease) or cecal intussusception (e.g., hematochezia despite relatively normal stools, bloody diarrhea not diagnosed with rigid colonoscopy). Flexible gastroduodenoscopes are preferred; however, larger diameter human colonoscopes can be used. If ileoscopy is desired, it is best to use smaller diameter (i.e., < 9.8 mm) equipment. Preparing for the procedure involves removing feces. This is done by a combination of restricting food (for at least 12 hours for proctoscopy and for at least 24 and preferably 48 hours for colonoscopy of the descending colon and especially procedures that evaluate the ascending colon and ileo-ceco-colic valve area) and removing the feces that are already there (i.e., enemas and/or lavage solutions). Dogs which have been fasted for 12 h and have had 2 sets of warm water enemas can still have a lot more fecal matter than is desirable. Intestinal lavage solutions are very helpful, but are not always cost-effective and they do not ensure that the colon will be as clean as you wish. Lavage solutions such as Golytle® can be administered the day before the procedure (i.e., 25 ml/kg per os, twice, each administration 1 hour apart) or the morning of the procedure (10 ml/lb/hour via a NE tube, for 4 hours the morning before the procedure). Be careful, it is possible (not likely but possible) that one can cause GDV in large dogs by administering large volumes of liquid in this manner. In dogs, enemas should be "high, hot, and a whole, whole lot." Simply putting the enema tube a couple of inches into the rectum and letting water flow in is usually a worthless waste of time and effort. Gently insert the tube as far into the colon as it will go without effort, allow water to flow by gravity until the enema water is squirting out of the rectum in a vigorous stream. During this time, gently move the tube back and forth while the water is entering the colon to help loosen feces. Dogs 10–20 lb often tolerate 500 ml of water per enema (that takes into account having a lot of it "shooting" back out the rectum while you are administering the fluids). In dogs over 20 lb, we routinely administer 1 L at a time (again, assuming that a lot of it is squirting out while we are administering the enema). If at any time the patient is in pain (as opposed to discomfort) or becomes nauseated, stop the infusion of the enema fluid. In cats, you cannot administer the enema fluid by gravity flow lest you over distend the colon (usually seen as vomiting); use a 50 cc syringe and slowly fill the colon without trying to get the cat to eliminate water during the procedure. In both dogs and cats, we typically administer 5 mg of bisacodyl after the enemas given the night before the procedure.
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