Intestine: obstruction

• Bowel obstruction is a frequent occurrence and is the most common indication for surgical intervention involving the gastrointestinal tract. Classified as simple (mechanical or functional) or strangulated Intestine: strangulated obstruction (hernia).
• Cause: foreign bodies, tumors (lymphosarcoma Lymphoma , annular adenocarcinoma Adenoma / adenocarcinoma ), strictures due to trauma or prior surgery, intussusception, abscesses or adhesions (rarely).
• Signs: variable depending on location of obstruction - may include vomiting, dehydration, abdominal pain, endotoxic shock, perforation, death.
• Diagnosis: plain radiography usually adequate but not for radiolucent causes.
• Obstructions can be high (proximal) involving the pylorus, duodenum and the proximal jejunum or low (distal) small bowel obstruction involving the lower half of the jejunum and ileum.
• Treatment: surgery.
• Prognosis: higher mortality rates are associated with strangulation and high obstructions Intestine: strangulated obstruction (hernia).

• Vomiting (present) - persistent, acute onset.
• Dehydration.
• Hypovolemic shock.

• Intermittent vomiting - persistent, acute onset.
• Dehydration.
• Weight loss.

• Anorexia.

• Acute vomiting.
• Severe abdominal pain.
• Shock.

• Requires surgical intervention. Endoscopic removal is possible with some proximal duodenal and pyloric foreign bodies.

• Foreign bodies Intestine: linear foreign bodies.
• Tumors (lymphosarcoma, annular adenocarcinoma).
• Intussusception Intussusception.
• Strictures due to trauma or prior surgery.
• Abscesses.
• Congenital defects.
• Adhesions.

• Obstruction interferes with passage of luminal contents along the intestine.
• Distention of bowel occurs proximal to obstruction with fluid and/or gas and food.

• Foreign bodies may cause damage which varies according to their shape and size:
• • Laceration.
  • Obstruction.
  • Pressure necrosis.
  • Perforation.

Proximal obstruction

• High intramural pressure → compromised blood supply → possible shunting away from intestinal capillaries to arteriovenous anastomoses → hypoxia to the bowel, loss of viability and increased permeability to toxins, including endotoxins.
• Duodenum is more sensitive to circulatory changes associated with distension.

Obstruction proximal at pylorus

• Hydrogen ion loss → metabolic alkalosis often with hypokalemia.

Obstruction below the pancreatic and biliary ducts

• Vomiting and loss of absorption of fluid collecting proximal to the obstruction → rapid and severe losses with significant amount of bicarbonate ion → dehydration and/or hypovolemic shock → metabolic acidosis.

Distal obstruction

• Fluid and electrolyte losses less severe but significant in chronic cases.
• Less severe distension of intestinal wall → circulation of affected gut unimpeded.

Strangulation

• Partial or total obstruction of venous drainage and an intact arterial supply → intramural sequestration of blood and eventually bowel wall edema.
• Distended bowel proximal to the strangulation filled with gas and fluid containing a significant amount of blood → non-viable and necrotic bowel wall → transmural migration of toxins and bacteria → hypovolemia, endotoxic shock and death.

• Hours to days for acute obstruction.
• Partial or intermittent obstructions may show signs over weeks to months.

• Vomiting.
• Abdominal pain.
• Abdominal mass.
• Weight loss.
• Anorexia.

• Vomiting Vomiting.
  Acute onset, persistent vomiting in a previously healthy, young dog is almost always from intestinal foreign body.
• Anorexia.
• Weight loss.

• Depression.
• Death.

• Dehydration.
• Signs of shock:
  • Tachycardia.
  • Poor pulse quality.
  • Poor peripheral perfusion.
• Abdominal pain.
• Palpable abdominal mass.

• Pyrexia.

• Abdominal films Radiography: abdomen.
• Radiopaque foreign body visible.
• Gas and fluid accumulation causing bowel distension on VD or lateral view  proximal to obstruction. Very proximal obstructions may show no distension.
• 'Gravel' (multiple small radiopacities) accumulation proximal to obstruction.
• Signs associated with underlying cause:
  • Linear foreign bodies; stacked appearance of intestines - indicates chronic partial obstruction.
  • Intussusception; soft tissue mass Intussusception and coiled watch-spring appearance.
  • Strangulated obstruction (+hernia); loops of intestine outside peritoneal cavity Intestine: strangulated obstruction (hernia).

• Obstruction to passage of contrast agent .
• Rarely necessary as diagnosis can usually be made from plain films +/- signs.
• May highlight radiolucent foreign body.
• Barium administration produces better intestinal contrast and therefore more useful in diagnosis of etiology of ileus.
• Iodine-based contrast media may be advocated in cases of suspected intestinal perforation (or if surgical intervention anticipated) however these produce less useful radiographs and hypertonicity may result in further fluid accumulation within bowel lumen.
  If surgical intervention anticipated exploratory laparotomy will provide more information than any form of contrast radiography

• Laparotomy Laparotomy: midline may be the most straightforward method of definitive diagnosis.

• Foreign body may be visible.
• Useful in ruling out other causes of acute abdominal signs, eg pancreatitis, intussception, etc.
• Classic 'jelly roll' or 'swiss roll' appearance of intussusception.

• To rule out other (systemic) causes of vomiting.
• Electrolyte concentrations, eg sodium Blood biochemistry: sodium and potassium Blood biochemistry: potassium should be measured as imbalances are common in vomiting patients.

• Stabilization:
  • Intravenous fluid therapy Fluid therapy.
  • Electrolyte correction and stabilization is essential.
  • Antibiotics and acid-base balance.
• Surgical correction once patient stabilized.

• Enterotomy or enterectomy for removal of obstruction.
• Resection of ischemic and non-viable bowel at time of obstruction removal.

• Observation for acute dehiscence of bowel incision.

Monitoring

• Electrolyte and acid-base imbalance.

• Good if obstruction relieved promptly.

• Cessation of vomiting after removal of obstruction.
• Return to normal gastrointestinal function.

• To resect non-viable bowel at time of surgery.
• Poor healing/leakage at anastomosis.
• Intestinal perforation carries poor prognosis.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Graham J P, Lord P F & Harrison J M (1998) Quantitative estimation of intestinal dilation as a predictor of obstruction in the dog. JSAP 39 (11), 521-4 PubMed.
• Shaiken L (1997) Determining the type of intestinal obstruction. Vet Med 92 (11), 950-951 VetMedResource.