Gastrointestinal obstruction is partial or complete blockage of the GI tract. GI obstruction often leads to intractable vomiting, the consequences of which can be life-threatening and may include aspiration pneumonia, electrolyte and acid-base disturbances, and dehydration. Depending on the obstruction's underlying cause, the obstructed site can undergo tissue damage, resulting in perforation, endotoxemia, and hypovolemic shock. Therefore, GI obstruction should be treated as an emergency.
Etiology and Pathophysiology of Gastrointestinal Obstruction in Small Animals
GI obstruction can be secondary to extraluminal, intramural, or intraluminal causes.
The most common cause of extraluminal 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 but may occur elsewhere. Gastroesophageal and pylorogastric intussusceptions are uncommon, acute, severe forms of intussusception associated with a high mortality rate. German Shepherd Dogs may be predisposed to gastroesophageal intussusception. Other causes of extramural obstruction include intestinal entrapment with intestinal volvulus (torsion), hernias, or mesenteric rents. Extramural obstructions can result in bowel strangulation, loss of blood supply, and rapid development of hypovolemic shock.
Intramural obstruction can be caused by infiltrative diseases such as neoplasia, fungal infection (eg, pythiosis), and granulomas (eg, secondary to feline infectious peritonitis). Pyloric stenosis can cause gastric outflow obstruction with the intramural obstruction secondary to thickening (hypertrophy) of the pyloric muscles. This has been reported as a congenital condition in brachycephalic breeds. Pyloric stenosis may also occur later in life, particularly in smaller-breed dogs such as Lhasa Apsos, Shih Tzus, and Maltese; however, the cause is usually unknown.
Intraluminal obstruction can occur in any species. The problem commonly occurs in dogs and cats most often secondary to ingestion of a foreign body. Cats can also develop intraluminal obstructions secondary to trichobezoars.
The obstruction can occur anywhere from the esophagus through the colon.
GI obstruction may be due to one or more foreign bodies. 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. Very small objects (eg, a pencil eraser) may cause obstructions in small patients such as small cats or ferrets.
Obstructions secondary to foreign body ingestion can be partial or complete if the object is unable to pass through the GI tract. Large, round objects often result in complete obstruction. Linear or small foreign bodies are more likely to cause partial obstruction. Linear foreign body obstructions are associated with a higher risk of intestinal perforation; in these cases, one end of the foreign body often gets stuck (typically at the base of the tongue or stomach), while the other end continues to migrate through the intestines through peristalsis, causing the intestines to bunch up and the foreign body to saw through the intestinal wall.
Regardless of underlying cause, unresolved GI obstruction leads to distention of the more proximal GI tract with fluid and gas. If GI loops become entrapped in hernias or mesenteric rents, strangulation and bowel incarceration occur. Venous return is impaired, but arterial flow is maintained, leading to congestion, anoxia (lack of oxygen), and necrosis. Obstruction or strangulation of bowel can result in GI tissue devitalization 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.
Epidemiology of Gastrointestinal Obstruction in Small Animals
Young cats and young large-breed dogs are more likely to develop foreign body obstruction than older animals. Dogs are more likely than cats to ingest a foreign body and develop a GI obstruction. Cats are more likely to develop intestinal obstruction from a linear foreign body.
There is no sex predisposition.
Behavioral disorders (eg, pica) and illnesses or medications causing polyphagia are risk factors.
Clinical Findings of Gastrointestinal Obstruction in Small Animals
Clinical signs of GI obstruction may include anorexia, regurgitation, vomiting, diarrhea, lethargy, or shock, depending on the location, duration of obstruction, and other comorbidities.
Clinical signs of GI obstruction are variable but often include vomiting and anorexia. Diarrhea, weight loss, lethargy, and clinical signs of septic shock are less common. Vomiting may be less common with distal small intestinal obstructions.
Physical examination may be unremarkable or may reveal clinical 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 (see linear foreign body image).
If a linear foreign body is present in the oral cavity, it must never be pulled in hopes of retrieving the foreign body, because it may be embedded in the tissue and pulling may lead to perforation. Instead, the linear foreign body should be cut at its anchor point, which will help facilitate its abdominal removal (or may allow it to pass through in rare cases).
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Courtesy of Dr. Kevin Winkler.
With the acute loss of blood supply, clinical signs of hypovolemic shock and abdominal pain usually accompany cases of intestinal incarceration or volvulus.
Diagnosis of Gastrointestinal Obstruction in Small Animals
History and clinical signs
Clinicopathological findings
Radiography and ultrasonography
GI obstruction may be suspected based on a history of witnessed foreign body ingestion or based on clinical signs.
Relevant diagnostic testing may include a CBC and serum biochemical analysis.
Hemogram 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 with 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 (1). 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 (see intestinal obstruction radiographs; see also ileocecocolic intussusception radiographs). 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 occur with other causes of GI obstruction, including intestinal stricture, adhesions, intussusception, and neoplasia.
Courtesy of Dr. Thomas Gibson.
Courtesy of Dr. Thomas Gibson.
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; however, if GI perforation is suspected, aqueous iodine or iohexol should be used instead.
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Abdominal ultrasonography can help identify the presence of GI foreign bodies and dilation of intestinal loops with fluid (see intestinal intussusception ultrasonogram). Transverse sonographic views of intestinal intussusceptions often show a targetlike lesion with concentric hyperechoic and hypoechoic rings.
Courtesy of Dr. Kevin Winkler.
Large amounts of intestinal gas may obscure the ultrasonographic view.
Clinical signs of peritonitis and GI perforation detectable with radiography or ultrasonography include abdominal effusion and free gas. Abdominal effusion, if present, should be cytologically examined to evaluate for septic peritonitis.
Radiographic signs of mesenteric (intestinal) volvulus show distention of the small bowel with poor abdominal detail (see intestinal volvulus radiographs). These findings may be confused with cases of ileus. Repeating radiographs will frequently show rapid progression of intestinal distention with a mesenteric volvulus.
Courtesy of Dr. Kevin Winkler.
Treatment of Gastrointestinal Obstruction in Small Animals
Supportive care
Surgery, if indicated
In most cases, removal of detected foreign bodies via endoscopic or surgical retrieval is recommended because of the potential for obstruction or perforation. However, some foreign bodies (especially small and smooth ones) may pass through the GI tract without requiring surgery. The decision to treat medically or proceed with surgery can be a challenge.
Passage of radiographically detected GI foreign bodies can be monitored with serial radiographs, provided that the animal is clinically stable. In these patients, radiographic monitoring should be performed to ensure passage of the foreign material is progressing. Failure of these objects to pass within 36–48 hours, serial radiographic evidence that they are not moving, or deterioration of clinical signs necessitates surgical removal. If clinical signs of vomiting, depression, and lethargy continue, surgical intervention is recommended immediately.
Most cases of acute vomiting are not a result of GI obstruction and are frequently 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 clinical 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 radiography or ultrasonography should be performed to identify masses, foreign objects, or clinical signs of intestinal distention that may indicate a possible obstruction.
When treating a GI obstruction, fluid and electrolyte abnormalities and acid-base deficits should be corrected before surgery, if possible.
Prophylactic, broad-spectrum antimicrobials should be considered before intestinal surgery.
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 and therefore should not be used for suspected linear foreign bodies. 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, clinical 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 or future complications from intestinal adhesions.
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 difficult to palpate, making assessment of its length difficult.
Multiple solid, smooth intestinal foreign bodies can often be “milked” through the intestine and removed through one incision. However, 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.
An appositional suture pattern should be used to minimize the risk of postoperative GI leakage. Intussusceptions are manually reduced or resected with the remaining bowel anastomosed if successful reduction is not possible.
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 antimicrobials and closed suction drains. Gastric decompression via a nasogastric tube, antiemetics, and motility-modifying medications may be used if nausea is still present.
If the animal is not vomiting, water may be offered 12 hours after anesthesia recovery. Food may be introduced 12–24 hours after recovery if there is no vomiting.
Prognosis and Prevention of Gastrointestinal Obstruction in Small Animals
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) and the administration of glucocorticoids are associated with a higher rate of postoperative dehiscence.
Animals developing clinical signs of peritonitis or sepsis have more postoperative complications and are at higher risk of enterotomy dehiscence. Animals 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 the prognosis depends on the type of neoplasia.
Mesenteric volvulus is associated with a high mortality rate. Even with rapid intervention, the entire small bowel may be irreversibly compromised.
Key Points
Causes of GI obstruction vary. Foreign bodies, neoplasia, and intestinal accidents such as intussusceptions must be considered.
Clinical signs vary with the location and degree of obstruction.
Imaging (radiography with or without contrast, ultrasonography) detects most obstructions.
Dilation of the GI tract occurs proximal to the obstruction.
Careful surgical exploration of the abdomen may be required to remove the source of obstruction, evaluate the viability of the compromised GI tract segment, and resect devitalized tissues.
For More Information
References
Boag AK, Coe RJ, Martinez TA, Hughes D. Acid-base and electrolyte abnormalities in dogs with gastrointestinal foreign bodies. J Vet Intern Med. 2005;19(6):816-821. doi:10.1892/0891-6640(2005)19[816:aaeaid]2.0.co;2
