Enterotomy: Small intestinal anastomosis (Proceedings)

Small Intestinal Healing

Layers of the intestinal wall include mucosa, submucosa, muscularis, and serosa. Mucosa is important because it provides a barrier that separates the luminal environment from the abdominal cavity. Mucosa and intestinal blood supply are important for normal intestinal secretion and absorption. Submucosa is the intestinal layer that provides mechanical strength and must be engaged when suturing intestine. The submucosal layer provides blood vessels, lymphatics, and nerves. The muscularis is needed for normal motitliy. Serosa is important in forming a quick seal at a site of injury or at an incision.

Intestinal healing dependent on good blood supply, accurate mucosal apposition and good tissue handling. Approximating suture patterns facilitate rapid healing of the intestine, while everting and inverting suture patterns slow intestinal healing and may result in lumen stenosis. Healing is also enhanced by the omentum, which helps seal the wound and contributes to the blood supply of intestinal. Healing of the intestine is influenced by systemic factors such as hypovolemia, hypoproteinemia, debilitation and concurrent infection. Tension on the anastomosis caused by ingesta, fluid, gas, or ileus increases the potential for intestinal dehiscence.

The three phases of wound healing overlap with the lag phase occurring during days 0 to 4 and is associated with inflammation and edema of the intestinal wound. A fibrin seal forms during the first few hours, although this contributes to early wound strength, most of the wound strength is attributed to sutures. Healing is biomechanically weakest at the end of the lag phase because fibrinolysis and collagen deposition and therefore dehiscence commonly occurs between day 3 and 5. The proliferative phase of healing occurs between days 3 and 14. Fibrous repair occurs, which is followed by a rapid gain in wound strength. The strength of the repair site approximates that of normal intestine 10 to 17 days following repair. The maturation phase occurs between 10 to 180 days and this is when collagen is reorganized and remodeled during the healing phase.

Wound Classification and Antibiotic Use:

All surgeries that involve entering the intestinal lumen are classified as clean-contaminated or contaminated procedures depending on the amount of spillage that occurs during surgery. Post operative infections following contaminated surgery increases with patient stress, organism pathogenicity, tissue susceptibility, and duration of surgery. Common pathogens responsible for peritonitis following intestinal surgery are E. Coli, Enterococcus spp., and coagulase-positive Staphylococcus aureus.

Bacterial numbers are less in the duodenum and jejunum (upper and middle intestine) than in the ileum, colon, and rectum. Holding animals off food decreases bacterial numbers in the stomach and small intestine. Prophylactic antibiotics are indicated in animals undergoing intestinal surgery. First generation cephalosporins (cefazolin) should be administered 20 minutes before surgery involving the upper and middle small intestine, while second generation cephalosporins (cefmetazole or cefoxitin) should be administered for procedures involving the distal small intestine and large intestine. Antiobiotics should be redosed 2 hours after the initial dose and discontinued after surgery. Antibiotics should be continued in the postoperative period only if the animal is septic from peritonitis.

Enterotomy

Definition: an incision into the lumen of a segment of small intestine.

Indications: foreign body removal, full thickness intestinal biopsy, linear foreign body removal

Celiotomy and Full Thickness Biopsy

Performed if endoscopy or ultrasound biopsy if not possible or is nondiagnostic. Enterotomy allows collection of full-thickness biopsies from all areas of the intestine and other abdominal structures.

Longitudinal or transverse enterotomy incisions can be made to collect samples. Multiple biopsies should be performed and samples should be reasonably large (5-10 mm) and contain adequate amounts of mucosa.

Procedure

Exteriorize and isolate the diseased or desired intestine from the abdomen and pack laparotomy sponges around the intestinal segment to decrease contamination.

Gently milk chyme from the lumen of the identified intestinal segment. This minimizes spillage of chyme during the enterotomy procedure.

To further minimize spillage of chyme, occlude the lumen at both ends of the isolated segment by having an assistant use a scissorlike grip with the index and middle fingers, approximately 4 to 6 cm on each side of the proposed enterotomy site. If an assistant is not available a Doyen (noncrushing intestinal forcep) or sterile bobypins can also be used to occlude the intestinal lumen.

Make a full thickness stab incision into the lumen on the antimesenteric border with a No. 11 scapel blade. Obtain full thickness biopsies 2 to 3 mm wide by either making a second longitudinal incision parallel to the first with the scapel blade or by removing an ellipse of intestinal wall at one margin of the first incision with Metzenbaum scissors.

If a foreign body is present, make the incision in healthy-apprearing tissue distal (aboral) or proximal to the foreign body. Lengthen the incision along the intestine's long axis with Metzenbaum scissors or scalpel as necessary to allow foreign body removal without tearing the intestine.

Transverse enterotomy incisions can also be made to obtain biopsies but is not recommended for foreign body removal.

After isolating and preparing the section of intestine to be biopsy as mentioned above place a sterile tongue depressor behind the intestine to act as a "cutting board" and making a "V" incision initiated at the antimesenteric border.

Make a single 3mm incision with a No. 11 scapel blade starting at the antimesenteric border and extending toward the mesenteric border. This incision should be angled approximately 30°, making the first limb of the "V". Make a second incision starting 3mm from the first incision angled toward the distal portion of the first incision creating the second limb of the "V".

Closure of Enterotomies

IF NECESSARY prepare the incision for closure by trimming everted mucosa so that its edges are even with the serosal surface.

Use a monofilament absorbable suture material on a swaged-on taper needle. For medium and large dogs 3-0 polydioxanone (PDS) or polyglyconate (Maxon) suture should be used. For small dogs and cats 4-0 polydioxanone (PDS) or polyglyconate (Maxon) suture should be used. Consider a monofilament nonabsorbable suture (polypropylene or nylon) if the patient has an albumin level less than or equal to 2.0 g/dl. Never use chromic gut or gut for intestinal surgery.

Close the enterotomy with simple interrupted appositional pattern. I close the enterotomy longitudinally but some surgeons recommend closure of the enterotomy in a transverse fashion to increase intestinal lumen diameter.

Sutures should be placed through all layers of the intestinal wall, 2mm from the edge and 2 to 3 mm apart, with extraluminal knots.

Angle the needle so the serosa is engaged slightly further from the edges than the mucosa to help prevent mucosal evertion.

Tie each suture carefully with apposition without cutting through the serosa layer of the intestine. Sutures should be tied just tight enough to appose all layers of the intestine.

Before releasing luminal occlusion near the enterotomy leak test the enterotomy by tunneling a 20-22 gauge needle into the lumen of the intestine and injecting sterile saline into the lumen. Inject just enough saline to distend the enterotomy site. If leakage does occur place one or two more sutures and retest the enterotomy site for leakage.

Lastly wrap a small amount of omentum around the enterotomy site. This will help seal the enterotomy site.

Complications

The biggest complication associated with an enterotomy procedure is dehiscence leading to septic peritonitis.

Intestinal Resection and Anastomosis

Definition: an intestinal resection and anastomosis is an enterectomy (removal of a segment of intestine) with resestablishment of continuity between the divides ends.

Indications: removing ischemic, necrotic, neoplastic, or fungal-infected segments of bowel. Irreducible intussusceptions are also managed by resection and anastomosis.

Procedure:

Make an abdominal incision long enough to allow exploration of the abdomen. This usually requires an incision from xphoid to pubis. Exteriorize and isolate the diseased intestine from the abdomen by packing with towels or laparotomy sponges.

Assess intestinal viability and determine the amount of bowel that needs to be resected. Color, palpation and the "pinch test" determine intestinal viability. Pinching a section of bowel to see if a peristaltic wave can be initiated is called the "pinch test".

Double ligate and transect the arcadial mesenteric vessels from the cranial mesenteric artery that supplies the segment of intestine that will be removed. Next double ligate the terminal arcade vessels within the mesenteric fat at the points of proposed intestinal transection. 3-0 PDS on a swaged taper needle is recommended for medium and large dogs to ligate the arcadial mesenteric vessels and the terminal arcadial vessel. It is sometimes difficult to visualize the terminal arcade vessel in an obese animal due to the large amount mesenteric fat.

Gently milk chyme from the lumen of the identified intestinal segment and occlude the lumen at both ends of the segment to minimize spillage of intestinal contents. (See enterotomy). Place forceps across each end of the diseased bowel segment. These forceps may be either crushing (Carmalts) or noncrushing (Doyens) because this segment of bowel will be removed.

Transect the intestine with either a scalpel blade or Metzenbaum scissors along the outside of the forceps. Make the incision either perpendicular or oblique to the long axis of the intestine. Use a perpendicular incision at each end if the luminal diameters are equal in size.

When luminal diameters are not equal use a perpendicular incision across the intestine with the larger diameter and an oblique incision (45 to 60 degrees) across the intestine with the smaller luminal diameter to help correct size disparity. Make the oblique incision so the that the antimesenteric border is shorter than the mesenteric border. If necessary trim the everted mucosa with Metzenbaum scissors just before beginning the end-to-end anastomosis. Use 3-0 (medium and large dogs) or 4-0 (small dogs and cats) monofilament, absorbable suture (PDS or Maxon) with a swaged-on-taper needle. In cases of peritonitis or neoplastic disease polypropylene or nylon is recommended. Place simple interrupted sutures through all layers of the intestinal wall and angle the needle so the serosa in engaged slightly further from the edge than the mucosa, which helps prevent muscosal evertion. Tie each suture carefully to appose all layers of the intestine with the knots located extraluminally. Remember that the submocosa is the main holding layer in all sections of the GI tract. Some surgeons prefer a simple continuous pattern. Pulling continuous sutures too tight will have a purse-string effect, which may compromise intestinal lumen diameter leading to stenosis or obstruction. Appose intestinal ends by first placing a simple interrupted suture at the mesenteric border. This is an important suture because most intestinal dehiscence occurs at the mesenteric border. It may be necessary to dissect some of the mesenteric fat to properly visualize and place this suture. Next, place a second suture at the antimesenteric border approximately 180 degrees from the first suture. This divides the suture line into equal halves. If the luminal diameters are of equal diameter, space additional sutures between the first two sutures approximately 2 mm from the edges and 2 to 3 mm apart. If minor disparity exists between lumen sizes, space sutures around the larger lumen slightly further apart than the sutures in the intestine with the smaller lumen. To correct luminal disparity that cannot be accommodated by first angling the incision or by suture spacing, resect a small wedge (1 to2 cm long and 2 mm wide) with Metzenbaum scissors from the antimesenteric border of the intestine with the smaller luminal size. This will enlarge the perimeter of the stoma, giving it an oval shape. After suture placement, inspect the anastomosis and check for leakage as performed for enterotomies. This is a subjective test because all anastomoses can be made to leak if enough pressure is applied. Place additional sutures if leakage occurs. The mesenteric defect should be closed with a simple interrupted or continuous pattern of 4-0 PDS or Maxon on a swaged on taper needle. It is imperative that you do not penetrate or damage the arcadial vessel near the defect. The abdomen should be thoroughly lavaged with warm saline and the anastomotic site should be wrapped with omentum before abdominal closure.

Complications

The biggest complication associated with intestinal resection and anastomosis is dehiscence of the anastomoses site. Other complications include shock, leakage, ileus, peritonitis, intestinal stenosis and short bowel syndrome. Short bowel syndrome may occur if large segments (more than 70% to 80%) of small intestine are removed. Weight loss, diarrhea, and malnutrition are the predominate clinical signs. If accidental spillage of intestinal contents occurs the abdomen should be thoroughly lavaged with warm saline (the solution to pollution is dilution).