CHAPTER 11 Small Bowel Resection
Case Study
Supine and upright abdominal radiographs show dilated loops of small bowel, air–fluid levels, and minimal air in the colon, consistent with a small bowel obstruction. A computed tomography (CT) scan of the abdomen and pelvis shows dilated loops of small bowel and a point of transition to collapsed bowel in the right lower quadrant (Fig. 11-1).
INDICATIONS FOR SMALL BOWEL RESECTION
I. Small Bowel Obstruction
A. Postoperative adhesions are the most common cause of small bowel obstruction. Other etiologies include hernias (e.g., inguinal and femoral), volvulus, intussusception, benign and malignant tumors, Crohn’s disease, gallstone ileus, foreign bodies, parasites, bezoars, and radiation enteritis. Bowel obstructions are classified as complete or partial. This distinction is often inferred from the severity of clinical symptoms and radiographic findings (e.g., absence of colonic air on abdominal radiograph). Patients with a bowel obstruction typically present with nausea and vomiting, diffuse abdominal pain, abdominal distention, and obstipation. Dehydration may result from vomiting and GI fluid secretion into obstructed bowel. A potential endpoint of many obstructive processes is bowel ischemia. This may result from compromise of the vascular supply to the small bowel in an incarcerated hernia (strangulation) or from progressive distention of obstructed bowel, leading to increased wall pressure, obstruction of venous outflow, and subsequent arterial compromise.
B. The initial management of a small bowel obstruction includes nasogastric tube (NGT) decompression and fluid resuscitation. Small bowel obstructions resulting from adhesions are more likely to resolve without surgical management than are obstructions from other causes. Focal or worsening abdominal tenderness, signs of peritonitis, fever, hemodynamic instability, leukocytosis, and lactic acidosis, suggesting bowel compromise, require urgent operative exploration. In addition, patients with complete obstructions and those without a history of abdominal surgery are more likely to require early operative intervention. Operative management is primarily aimed at relieving the obstruction, which may require lysis of adhesions, hernia repair, or bowel resection.
II. Perforation may result from bowel necrosis as a result of a number of processes, including small bowel obstruction and acute mesenteric ischemia. Alternatively, perforation may occur without preceding necrosis of the small bowel wall (e.g., perforated small bowel tumors, perforated duodenal ulcers, and Crohn’s disease). Patients typically present with fever, hemodynamic instability, and focal or generalized peritonitis. With few exceptions, bowel perforations mandate immediate surgical exploration and resection of perforated segments.
III. Bleeding from the small bowel may be caused by small bowel tumors or by Meckel’s diverticulum. In the latter case, bleeding is usually caused by exposure of the surrounding small bowel mucosa to secretions from ectopic gastric mucosa within the diverticulum. Small bowel arteriovenous malformations and hemangiomas are two additional sources of small bowel bleeding.
IV. A fistula is defined as an abnormal connection between two epithelialized surfaces. Some examples of small bowel fistulas include enterocutaneous fistulas (fistula between bowel and skin) and fistulas between the small bowel and the urinary tract or vagina. Small bowel fistulas may result from iatrogenic bowel injuries during surgery or an anastomotic leak after bowel resection. Additionally, cancer, Crohn’s disease, infection, and radiation may all lead to fistula formation. Initial treatment of a small bowel fistula usually consists of bowel rest and total parenteral nutrition (TPN) to decrease fistula output and optimize nutrition. In some patients, this treatment leads to closure of the fistula tract. However, in patients in whom conservative management is unsuccessful, surgery is performed to excise the fistula tract and resect involved segments of bowel.
V. Small bowel tumors may be benign (e.g., adenomas, lipomas, hamartomas, and leiomyomas) or malignant (e.g., adenocarcinomas, carcinoids, leiomyosarcomas, and lymphomas). When a benign or malignant small bowel tumor is diagnosed, segmental resection is performed to relieve symptoms or prevent progression. If a small bowel mass is suspicious for malignancy, it should be resected with wide margins and sampling of the regional mesenteric lymph nodes.
PREOPERATIVE EVALUATION
The preoperative evaluation for a small bowel resection frequently includes:
I. Laboratory Studies: Before a small bowel resection, a complete blood count and a chemistry panel are usually obtained. Leukocytosis may reflect an ongoing inflammatory or infectious process (e.g., Crohn’s disease). In the setting of a small bowel obstruction, leukocytosis is a concerning finding and is sometimes indicative of bowel ischemia or perforation. Electrolyte abnormalities and an elevated blood urea nitrogen : creatinine ratio are characteristic in patients who are dehydrated (e.g., bowel obstruction or high-output fistula). An elevated lactic acid level reflects hypoperfusion of tissues and is often a late finding indicating tissue ischemia. Measurement of albumin and prealbumin levels allows for an assessment of nutritional status in patients with fistulae or Crohn’s disease. In patients with suspected carcinoid tumors, obtaining a 5-HIAA (a serotonin metabolite) level may help confirm the diagnosis.
II. Abdominal Radiographs: Abdominal radiographs are frequently obtained as part of an evaluation of abdominal symptoms. Dilation of the stomach and proximal bowel, air–fluid levels, and absent colonic gas suggest bowel obstruction. Pneumoperitoneum, typically seen as free air under the diaphragm, suggests perforation. An obstruction series, which consists of several radiographs obtained with the patient in different positions (typically, supine and upright abdominal and upright chest radiographs) may increase the sensitivity of the radiographic evaluation compared with a single image.
III. CT Scan: CT scans are valuable in determining the degree of bowel dilation, the presence of pneumoperitoneum, the viability of bowel, or the presence of a mass. When a CT scan is performed to evaluate a small bowel obstruction, failure of oral contrast to pass beyond a transition point between dilated and collapsed bowel suggests complete obstruction. The use of oral and intravenous contrast allows for more detailed images and should be administered, if possible.
IV. Miscellaneous Studies: Several other studies may be useful in the evaluation of suspected small bowel pathology.
A. In an upper GI series with small bowel follow-through, the transit of oral contrast through the GI tract is observed under fluoroscopy. This study may help to localize points of obstruction, mucosal abnormalities, and fistulae.
B. A fistulogram involves the administration of contrast through an enterocutaneous fistula to delineate the anatomy of its tract.
C. A Meckel’s scan involves intravenous administration of technetium-99, which is taken up by ectopic gastric mucosa and allows for visualization of the majority of Meckel’s diverticula.
COMPONENTS OF THE PROCEDURE
Preoperative Considerations
Incision and Exposure
I. Small bowel resection is typically performed through a midline incision large enough to allow for adequate exposure of the entire abdominal cavity.
II. After abdominal entry, the small bowel is inspected by running the bowel. This is accomplished using one of two techniques. In the first technique, the ligament of Treitz is identified and the small bowel is examined antegrade to the ileocecal valve (Fig. 11-2). The second technique involves identification of the cecum and retrograde inspection of the bowel to the ligament of Treitz.
Resection
I. Once the entire small bowel has been evaluated, attention is focused on the area of small bowel pathology. Selection of appropriate margins for resection is guided by the pathologic process. For example, small bowel tumors should be resected with wide margins. In contrast, resections for Crohn’s disease should preserve as much bowel as possible.
II. An opening in the mesentery is created immediately adjacent to the bowel, at the proximal resection margin. Care must be taken to avoid injuring the vessels supplying the bowel margins, which will ultimately feed the anastomosis.
Stapled Anastomosis
I. Corresponding corners of the proximal and distal staple lines are opened to expose the lumen of each bowel segment. A jaw of the surgical stapler is then inserted into each lumen, and the bowel segments are brought together side-to-side (i.e., lengthwise) by firing the stapler (Fig. 11-3).
Hand-Sewn Anastomosis
I. A small bowel anastomosis can be created without the use of surgical staplers. The small bowel is sharply divided with a scalpel, leaving two open ends that are brought together in two layers. An inner layer reapproximates the mucosa, and an outer layer reapproximates the seromuscular layers.
II. Typically, the posterior half of the seromuscular layer is sewn first. The inner layer is then sewn circumferentially. Finally, the anterior half of the seromuscular layer is completed (Fig. 11-4).
POTENTIAL COMPLICATIONS
I. In addition to technical complications, a number of factors increase the risk of anastomotic dehiscence. These factors include tension on the anastomosis, poor blood supply, infection, malnutrition, and immunosuppression. Anastomotic dehiscence may result in abscess or fistula formation. Patients with an anastomotic dehiscence may present with symptoms ranging from delayed bowel function to septic shock. Management is dependent on the timing and severity of symptoms. Stable patients are frequently managed with bowel rest, antibiotic therapy, and percutaneous drainage of intra-abdominal collections. Worsening clinical status and the presence of intra-abdominal collections that are not amenable to percutaneous drainage are indications for operative re-exploration.
II. A variety of devastating conditions (e.g., midgut volvulus, mesenteric vascular occlusion, and traumatic mesenteric vascular injuries) necessitate extensive bowel resections. Short bowel syndrome results when insufficient bowel remains to support a patient’s nutritional needs. The syndrome is typically characterized by diarrhea, metabolic abnormalities, and nutritional deficiencies. Patients may require long-term nutritional support in the form of TPN delivered intravenously. However, long-term TPN is associated with a significant risk of infectious complications.
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