GI obstruction often leads to intractable vomiting, the consequences of which can be life-threatening and include possible aspiration, electrolyte and acid-base disturbances, and dehydration. Depending on the underlying cause of the obstruction, the site can undergo tissue damage resulting in perforation, endotoxemia, and hypovolemic shock. Therefore, GI obstruction should be treated as an emergency.
Etiology and Pathophysiology
GI obstruction can result from a number of extraluminal, intramural, or intraluminal causes. The most common extraluminal cause is intussusception, in which an invaginated segment of the GI tract becomes enveloped by an antegrade or retrograde segment. Intussusception can be secondary to endoparasitic infection, parvoviral infection, foreign body ingestion, or neoplasia, but is often idiopathic. The most common site of intussusception is the ileocecocolic junction. Gastroesophageal and pylorogastric intussusceptions are uncommon, acute, severe forms of intussusception that are associated with a high mortality rate. German Shepherd dogs may be predisposed to gastroesophageal intussusception. Intestinal entrapment in hernias or mesenteric rents can result in strangulation of bowel and rapid development of hypovolemic shock.
Intramural obstruction can be caused by infiltrative disease such as neoplasia, fungal infection (eg, pythiosis), and granulomas (eg, secondary to feline infectious peritonitis). Pyloric stenosis can cause gastric outflow obstruction and has been reported as a congenital condition in brachycephalic breeds.
Intraluminal obstruction commonly occurs in dogs and cats secondary to ingestion of a foreign body and may be partial or complete. Linear or small foreign bodies are more likely to cause partial obstruction, whereas large, round objects often result in complete obstruction. Foreign bodies are usually objects that cannot be digested (eg, plastic, rocks), are slowly digested (eg, bones), or are too large to pass through the GI tract. Dogs that are indiscriminate eaters often consume such objects, while cats more typically ingest linear foreign bodies (eg, string, yarn, dental floss) while playing with them.
Regardless of underlying etiology, unresolved GI obstruction leads to distention of the more proximal GI tract with fluid and gas. Entrapment of GI loops secondary to hernias or mesenteric rents results in strangulation and bowel incarceration. Venous return is impaired, leading to congestion, anoxia, and necrosis. Devitalization of GI tissue and translocation of bacteria such as Escherichia coli and Clostridium spp from the GI lumen to the tissue can result. If not corrected, edema, hemorrhage, mucosal sloughing, and eventually bowel necrosis occur.
Clinical Findings and Diagnosis
Intussusception is most common in young dogs. Intestinal intussusception typically causes signs of abdominal pain, vomiting, and diarrhea with or without blood. More proximal intussusceptions (ie, gastroesophageal, pylorogastric) result in vomiting and regurgitation.
Foreign body obstruction is also more common in younger animals. Clinical signs vary depending on duration, degree, and location of the foreign body but often include vomiting and anorexia. Vomiting is less common with distal small-intestinal obstruction. Diarrhea, weight loss, lethargy, and signs of septic shock are less common. Physical examination may be unremarkable or reveal signs of abdominal pain or a palpable intestinal mass. Inspection of the oral cavity may reveal linear foreign bodies, possibly anchored to the base of the tongue in cats.
Signs of hypovolemic shock and abdominal pain are usually seen in cases of intestinal incarceration.
Laboratory findings associated with GI foreign bodies include leukocytosis with a mild left shift. In cases of GI perforation and secondary bacterial peritonitis or sepsis, marked leukocytosis or leukopenia with a degenerative left shift can be present. Proximal GI obstruction is typically associated with hypochloremia, hypokalemia, and metabolic alkalosis, while more distal GI obstruction is associated with metabolic acidosis. In a recent study in dogs, hypochloremia and metabolic alkalosis were the 2 most common changes regardless of the site of GI obstruction. Hyperlactatemia and hemoconcentration (increased PCV and total solids) are also frequently identified.
Plain radiographs may assist in locating radio-opaque foreign bodies. Complete obstruction may result in radiographic changes such as ileus and intestinal loop dilation with fluid and/or gas, while linear foreign bodies can result in intestinal plication. However, these findings are not specific for GI foreign bodies and can be observed with other causes of GI obstruction, including intestinal stricture, adhesions, intussusception, and neoplasia. Contrast abdominal radiographs may be useful in detection of radiolucent foreign bodies that create filling defects and in cases of intussusception. Barium is commonly used for contrast radiographs, but if GI perforation is suspected, aqueous iodine or iohexol should be used instead.
Abdominal ultrasonography can help identify the presence of GI foreign bodies and dilation of intestinal loops with fluid. Transverse sonographic views of intestinal intussusceptions often show a “target-like” lesion with concentric hyperechoic and hypoechoic rings. Large amounts of intestinal gas may obscure the image. Signs of peritonitis and GI perforation detectable with radiography or ultrasonography include abdominal effusion or free gas. Abdominal effusion, if present, should be cytologically evaluated for septic peritonitis. Endoscopic examination can be useful in identifying foreign bodies and mass lesions.
Most foreign bodies should be removed, via endoscopic or surgical retrieval, because of the potential for obstruction or perforation. Some small, smooth foreign bodies may pass uneventfully through the GI tract; movement of the foreign body can be monitored with abdominal radiographs. If the foreign body is not moving, and if obstruction or worsening of clinical signs is apparent, intervention is required. Linear foreign bodies in the oral cavity must be cut and never pulled in hopes of retrieving the foreign body.
Colonic foreign bodies are often detected incidentally and usually do not need to be removed. If a colonic foreign body is causing clinical signs, endoscopic removal is preferred over surgically opening the colon. Fluid, electrolyte, and acid-base disturbances should be corrected before anesthesia if possible.
Endoscopic or surgical retrieval of GI foreign bodies is associated with a high survival rate. The utility of endoscopy is typically limited to retrieval of gastric foreign bodies. The endoscope should be passed into the small intestine as distally as possible for evaluation, and radiographs taken while the animal is still anesthetized to evaluate for additional foreign bodies.
Endoscopy cannot assess the GI tract distal to the pyloric or proximal duodenal region. If there is a foreign body distal to the pyloric region, foreign bodies at multiple locations, or signs of septic peritonitis, exploratory laparotomy is indicated. Exploratory laparotomy is also preferred over endoscopy in cases of suspected intussusception and obstruction secondary to a mass lesion. During surgery, the entire GI tract must be inspected for objects that could cause obstruction, vitality of the tract is assessed, and areas of perforation or ischemia resected. If a linear foreign body is present in the stomach and extends into the small intestine, gentle manipulation may free it from its distal attachments, allowing removal through the gastrotomy incision. Otherwise, multiple enterotomies may be indicated. Foreign bodies should be removed with as few enterotomies as possible to decrease the risk of postoperative dehiscence. Multiple solid, smooth intestinal foreign bodies can often be “milked” through the intestine and removed through one incision. Linear foreign bodies are more likely to cause mucosal damage and devitalization, and can affect a large section of the GI tract. Devitalized or perforated areas must be resected and the remaining GI tract anastomosed. Intussusceptions are manually reduced or resected; the remaining bowel is anastomosed if reduction is not possible or the bowel loop appears compromised. Enteroplication may be performed to help decrease risk of recurrence.
Peritonitis is treated with antibiotics and closed suction drains or open abdomen management. Food and water may be introduced 12 hr after recovery if there is no vomiting.
Prognosis and Prevention
If GI tract obstruction due to a foreign body is recognized and treated quickly, the prognosis is good. Animals with peritonitis or sepsis have more postoperative complications and are at higher risk of enterotomy dehiscence. Preoperative hypoalbuminemia is also associated with a higher rate of postoperative dehiscence. Animals with peritonitis or that require resection of a large amount of intestine leading to short-bowel syndrome have a guarded prognosis. Postoperative dehiscence requires a second emergency surgery and is associated with a high mortality rate.
Gastroesophageal and pylorogastric intussusceptions are associated with a high mortality rate, and rapid diagnosis and surgical intervention are essential to maximize survival. GI obstruction secondary to neoplasia is uncommon; prognosis depends on the type of neoplasia.
Last full review/revision March 2012 by Shauna L. Blois; Thomas W. G. Gibson