that occurs after prolonged contact with mucosal surfaces [10], and magnets can cause perforation secondary to tissue entrapment between two magnets or a magnet and metallic object [7,18–20].
Figure 5.1 Removal of solidified wood glue from the stomach of a dog. Note the length of incision necessary to remove a foreign body of this size.
Signalment, History, and Physical Examination
Young (mean 2.5–4.5 years), medium to large‐breed dogs are most commonly reported to have GI foreign bodies [2, 4, 11, 21, 22], although this is not consistent in all studies [23]. Most reported cats are also young [2] with the mean age of 1.8–2.7 years [2, 13]. Clinical signs depend on the duration since ingestion and the type, extent, and location of obstruction. Animals with acute or complete obstruction often present with lethargy, anorexia, vomiting, and abdominal pain. Dehydration may also be present due to a combination of vomiting and lack of water intake. Vomiting tends to be more common with upper GI obstructions and has been reported to be present for 0.04–60 hours before presentation [2]. Chronic or partial obstruction, particularly distal in the intestinal tract, may include the same signs in addition to weight loss and diarrhea; and hemorrhagic diarrhea has also been reported subsequent to ingestion of contaminated foreign bodies, such as used feminine hygiene products [2, 24, 25]. Animals may also present with seemingly unrelated clinical signs, such as respiratory distress subsequent to intrathoracic migration of a foreign body [26]. Animals presented immediately after witnessed ingestion of a foreign body or those with small or inconsequential foreign bodies frequently have no clinical signs [2, 4, 21, 24].
Foreign objects may or may not be identified on physical examination. Evans et al. reported that only 6% (2 of 32) of dogs with linear foreign bodies had the object visible under the tongue [11]. A second study showed that 3% of objects were visible in the oral cavity or at the anus, while 76% of the foreign bodies or the intestinal abnormalities resulting from such were palpable in either the awake (60%) or anesthetized patient [2]. Additional clinical signs such as fever, lethargy, abdominal pain, and abdominal distention may also be seen in patients with perforation and septic peritonitis, induced by a foreign body.
Laboratory Findings
Laboratory abnormalities depend on the type and extent of obstruction, as well as the duration and severity of clinical signs. Many of the clinicopathologic abnormalities result from dehydration and hypovolemia that accompany the obstruction. Dehydration may result in an elevated hematocrit, total protein, and urine specific gravity, as well as prerenal azotemia. Hypoproteinemia and hypoalbuminemia may occur in animals with GI perforation‐induced septic peritonitis or in those with chronic obstructions marked by long‐standing protein‐losing diarrhea. Elevations in hepatic enzymes, particularly alanine transaminase, may be seen as a consequence of hypovolemic shock and reduced hepatic perfusion. Preoperative hypoalbuminemia has sometimes been associated with postoperative dehiscence of anastomotic sites or mortality [23,27–31], but in other studies hypoalbuminemia had not increased these risks [32–34]. Toxic effects of some foreign bodies, such as those composed of zinc or lead, may precipitate toxin‐specific laboratory abnormalities.
Acid–base abnormalities are common in animals with foreign body obstruction. In a study of animals by Boag et al. [4], it was found that 74.6% had elevated bicarbonate, 51% had hypochloremia, 45.2% had metabolic alkalosis (base excess greater than reference range), and 40–45% had hyperlactatemia. There was no statistical association between biochemical abnormalities and location of the foreign body at surgery (proximal or distal to the duodenal papilla). Hypochloremic, hypokalemic metabolic alkalosis was identified in 12% of dogs with proximal GI obstructions and 13.7% of dogs with distal GI obstruction [4].
Biochemical evaluation of abdominal fluid can be an aid to identifying the presence of foreign body‐induced septic peritonitis. A blood to fluid glucose difference of greater than 20 mg/dl was 100% sensitive and 100% specific for the diagnosis of septic peritoneal effusion in dogs and 86% sensitive and 100% specific in cats. A blood to fluid lactate difference of 2.0 mmol/l or less was also 100% sensitive and 100% specific for the diagnosis of septic peritoneal effusion in dogs [35]. Use of a veterinary handheld glucometer results in a high incidence of false negatives in identification of septic peritonitis because the relatively low cellularity of peritoneal effusion falsely elevates fluid glucose compared with blood glucose, thus reducing the ratio between samples [36].
Imaging
Radiographs
Imaging is a critical component of the diagnostic workup in patients with suspected foreign body ingestion. Traditionally, abdominal radiographs have served as the initial imaging modality. The improved detail provided by digital (computed) radiography makes it more sensitive than conventional radiography in identifying GI foreign bodies [37]. Radiographic findings may include segmental small intestinal dilation, plication, or detection of a foreign body (Figure 5.2). Objective radiographic criteria for determination of small intestinal obstruction have been evaluated. Adams et al. compared the small intestinal diameter (SID) of cats to the dorsoventral height of the cranial end plate of the second lumbar vertebra (L2) and found that when the SID : L2 ratio was 3.0 or greater, the probability of a mechanical obstruction was greater than 70% [38]. In dogs, a value of 1.6 for the ratio of the SID to the height of the body of the fifth lumbar vertebra (L5) at its narrowest point was reported as the upper limit of normal intestinal diameter [39]. In that report, dogs with SID : L5 ratio equal to or greater than 1.95 had a greater than 80% probability of being obstructed [39].
Elser et al. evaluated utility of serial radiography in dogs and cats for identification of a foreign body obstruction when the initial radiographic images are inconclusive for the presence or absence of GI mechanical obstruction [40]. In that prospective cohort study, four blinded reviewers (two radiologists, one radiology resident, one criticalist) separately assessed the initial and the follow‐up radiographic studies, taken 7–28 hours after the initial set, for diagnosis of mechanical obstruction. An ultrasound served as the gold standard. For all reviewers, there was no significant change in accuracy for the diagnosis of mechanical obstruction using serial radiographs, suggesting that alternative imaging should be pursued in those patients where the suspicion of obstructive foreign body remains high [40].
Positive or negative contrast radiography can be used to identify GI foreign bodies when standard radiographic views are equivocal. While the use of positive contrast agents may be helpful, in many cases of complete obstruction the contrast material may not reach the foreign body either because of a lack of forward flow of ingesta or because of vomiting. In addition, these studies are time dependent and require repeated radiographs to document flow of contrast through the GI tract. If there is suspicion of perforation, positive contrast materials such as barium sulfate are contraindicated; iodinated contrast materials may be a better choice with respect to the impact of leakage of the material into the abdomen. Pneumogastrography, using air or carbonated beverages as the negative contrast medium, can also be useful for identifying intragastric foreign material [41]. Contrast radiography to aid foreign body elucidation has largely been replaced by ultrasound when available.
Figure 5.2 (a) A right lateral radiograph of a dog that ingested pebbles. Note the focal accumulations of pebbles in the pylorus and at the ileocolic junction (arrow) plus multiple gas‐distended small intestinal segments. (b) A right lateral radiograph of a dog with a linear foreign body, note the plication of the small intestine and gas segmentation.