Gastrointestinal Obstruction in Small Animals
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.
GI obstruction can be secondary to extraluminal, intramural, or intraluminal causes. The most common extraluminal cause of GI obstruction 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. Intestinal intussusception occurs most commonly at the ileocecocolic junction. Gastroesophageal and pylorogastric intussusceptions are uncommon, acute, severe forms of intussusception associated with a high mortality rate. German Shepherds 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.
Most cases of acute vomiting are not a result of GI obstruction and are self-limiting. Vomiting may be a result of dietary indiscretion, parasitic infection, bacterial or viral gastroenteritis, anxiety, or motion sickness. In these cases, treatment usually involves withholding food for a short period, feeding an easily digested diet, and offering small amounts of water frequently. Careful monitoring for persistent vomiting, depression, abdominal discomfort, and/or fever is critical. If vomiting persists, reevaluation is warranted. Abdominal palpation should be performed, looking for signs of a foreign body or abdominal discomfort. Careful examination of the oral cavity in cats, looking for evidence of yarn, thread, or needles, is important. Abdominal radiographs should be performed, looking for radiopaque foreign objects or signs of intestinal distention, indicating possible obstruction.
Obstruction secondary to foreign body ingestion can be partial or complete if the foreign body is unable to pass through the GI tract. 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. Some dogs are indiscriminate eaters and will consume such objects, whereas cats more typically ingest linear foreign bodies (eg, string, yarn, dental floss) while playing with them.
GI obstruction may be due to one or more foreign bodies. The decision to treat medically or proceed with surgery can be a challenge. Some small objects identified radiographically will pass through the GI tract. Passage of these objects can be monitored with serial radiographs if the animal is clinically stable. Failure of these objects to pass within 48 hr, serial radiographic evidence that the objects are not moving, or a deterioration of clinical signs necessitate surgical removal. Presence of uncooked bone matter in the stomach should be monitored but is usually resolved by normal digestive processes in the stomach.
Regardless of underlying etiology, unresolved GI obstruction leads to distention of the more proximal GI tract with fluid and gas. If entrapment of GI loops results secondary to hernias or mesenteric rents, strangulation and bowel incarceration occurs. Venous return is impaired but arterial flow maintained, leading to congestion, anoxia, and necrosis. Obstruction or strangulation of bowel can result in devitalization of the GI tissue and translocation of bacteria such as Escherichia coli and Clostridium spp from the GI lumen to the tissue. If not corrected, edema, hemorrhage, mucosal sloughing, and eventually bowel necrosis occur.
Intussusception occurs most commonly 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.
Young cats and young, large-breed dogs are more likely to present with signs of foreign body obstruction than older animals. Clinical signs are variable, 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 may reveal signs of abdominal pain or a palpable intestinal mass. Physical examination must be thorough and include inspection of the oral cavity, because linear foreign bodies in cats may be anchored to the base of the tongue. If a linear foreign body is present in the oral cavity, it must be cut immediately and never pulled in hopes of retrieving the foreign body.
Signs of hypovolemic shock and abdominal pain usually accompany cases of intestinal incarceration.
Laboratory findings associated with GI foreign bodies include leukocytosis with a mild left shift. Marked leukocytosis or leukopenia with a degenerative left shift can be present in cases of GI perforation and secondary bacterial peritonitis or sepsis. A wide variety of electrolyte and acid-base changes have been described. Proximal GI obstruction has typically been associated with hypochloremia, hypokalemia, and metabolic alkalosis, whereas more distal GI obstruction is associated with metabolic acidosis. In a study in dogs, hypochloremia and metabolic alkalosis were the two 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 diagnosis of GI obstruction in cases of radiopaque foreign bodies. Complete obstruction may result in radiographic findings such as ileus and intestinal loop dilation with fluid and/or gas, whereas linear foreign bodies can create intestinal plication. These findings are not specific for GI foreign bodies, however, and can be seen 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 ultrasound view. Signs of peritonitis and GI perforation detectable with radiographs or ultrasound include abdominal effusion or free gas. Abdominal effusion, if present, should be cytologically examined to evaluate for septic peritonitis. Endoscopic examination may help identify foreign bodies and mass lesions.
Small, smooth foreign bodies may pass uneventfully through the GI tract. If this approach is taken, monitoring with abdominal radiographs to track the movement of the foreign body is recommended. If the foreign body is not moving, and if obstruction or worsening of clinical signs is apparent, intervention is required.
In most cases, removal of detected foreign bodies via endoscopic or surgical retrieval is recommended because of the potential for obstruction or perforation. Detection of colonic foreign bodies is often incidental, and these usually do not require removal. 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 foreign bodies causing GI obstruction is associated with a high survival rate. The utility of endoscopy is typically limited to the retrieval of gastric foreign bodies. Endoscopy cannot assess the GI tract distal to the pyloric or proximal duodenal region. If endoscopy is used to retrieve a proximal GI foreign body, the scope should be passed into the small intestine as distally as possible for evaluation, with radiographs taken before recovery from anesthesia to exclude the presence of multiple foreign bodies.
An exploratory laparotomy is indicated if a foreign body distal to the pyloric region is present, if there are foreign bodies at multiple locations, if there are signs of septic peritonitis, or if endoscopy is not available. Exploratory laparotomy is also indicated over endoscopy in cases of suspected intussusception and obstruction secondary to a mass lesion. The entire GI tract must be inspected for objects that could cause obstruction. Vitality of the GI tract must also be 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 easily free the foreign body from its distal attachments, allowing removal through the gastrotomy incision. Otherwise, multiple enterotomies may be indicated. The minimal number of enterotomies possible to remove the foreign body or bodies is recommended to help decrease the risk of postoperative dehiscence. Linear foreign bodies in cats can be particularly challenging, because the foreign material may be a single piece of thread, yarn, or dental floss that is not palpable, which makes assessment of its length difficult. 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 GI mucosal damage and devitalization and can affect a large section of the GI tract. Devitalized or perforated areas of the GI tract must be resected, and the remaining GI tract anastomosed. Intussusceptions are manually reduced or resected, and the remaining bowel anastomosed if reduction is not possible or the bowel loop appears compromised. Laparoscopic-assisted exploration and foreign body retrieval is gaining popularity among veterinary surgeons with suitable expertise and equipment.
After foreign body retrieval, correction of fluid, electrolyte, and acid-base disturbances should continue. Peritonitis is treated with antibiotics and closed suction drains. If the animal is not vomiting, water may be offered 12 hr after anesthetic recovery. Food may be introduced 12–24 hr after recovery if there is no vomiting.
Outcome for animals with GI foreign body obstruction is good if the condition is recognized and treated quickly. Animals with severe clinical signs resulting from systemic factors such as concurrent infection or debilitation, hypovolemia, and shock are at higher risk of delayed healing and incisional breakdown. Marked preoperative hypoalbuminemia (<2–2.5 g/dL) is associated with a higher rate of postoperative dehiscence. Animals presenting with signs of peritonitis or sepsis have more postoperative complications and are at higher risk of enterotomy dehiscence. Animals with signs of peritonitis, or those requiring resection of a large amount of intestine leading to short-bowel syndrome, have a guarded prognosis. Dehiscence of the intestinal surgical site most commonly occurs 3–5 days after surgery at the end of the lag phase of healing. Until this point, most tensile strength has been provided by formation of a fibrin seal that is debrided by macrophages 3–5 days after surgery. Postoperative dehiscence usually requires a second 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 chance of survival in these cases. GI obstruction secondary to neoplasia is uncommon, and prognosis depends on the type of neoplasia.