Gastrointestinal (GI) surgery can vary from very simple to highly complex depending on the state of the patient, the disease process being treated and the expertise of the surgeon. It is critical to understand the general principles of anatomy and physiology in order to achieve good surgical outcomes when intervening in the GI tract. In general, vascular supply to bowel is still evaluated using very simple clinical parameters as more objective methods have generally failed to translate into practical and reliable “in the clinic” assessment tools. Color, consistency, motility and bleeding/perfusion are still the four principal methods used to assess the vascular integrity of GI tissue. Knowledge of the blood supply to different parts of bowel is important to plan enteric incisions and anastomoses. The jejunum has generally obvious vascular arcades that lend themselves easily to planned ligation. The duodenum receives shared blood supply from the cranial and caudal pancreaticoduodenal arteries, branches of the celiac and cranial mesenteric arteries respectively as well as the gastroduodenal and right gastroepiploic in its most proximal aspect. When the descending portion of the duodenum requires resection, it is usually best to seal the duodenal blood supply directly at the antimesenteric margin in order to avoid damage to the pancreatic ductal system and blood supply. If a more extensive disease process dictates the resection of part of the pancreas, consideration should be given to making sure pancreatic tissue is resected in a way that avoids leaving areas of pancreas that are isolated from their ductal drainage system and therefore exocrine drainage mechanism. Care should also be taken in this area to make sure that the common bile duct is not involved in the disease process or is not impacted by the proposed resection.

The area around the ileocecocolic junction can also be challenging as it receives a mixed blood supply from the colic and ileocolic arteries. In this area, extensive collateral circulation appears to exists but direct visualization can be obscured by extensive fat deposition and the lymph nodes present within the mesenteric root. Much like in the duodenum, the safest course of action when performing an ileocolic resection is to take down the blood supply close to the mesenteric margin. The large intestine receives its blood supply from anastomosing branches of the colic arteries that arise from the cranial and caudal mesenteric arteries. These arteries, however, are not intimately associated with the mesenteric wall of the large intestine.

In contrast, they give off vasa recta which are short branches that emanate from the arteries and provide a segmental supply of blood along the length of the large intestine. In the case of large bowel resections these vasa recta are individually sealed by ligation or use of a vessel-sealing device between the colic arteries and the intestinal wall thus preserving optimal blood supply from the colic arteries.

Care should be taken if resection of the distal descending colon is planned to try and preserve as much of the cranial rectal artery, a branch of the caudal mesenteric which provides the principal arterial blood supply to this area of colon.

Many principles of bowel closure are common to all areas of the GI tract. When hand-sutured enterotomy closure or resection and anastomosis is performed, simple appositional suture patterns are usually preferred with the use of monofilament suture. Simple continuous and simple interrupted have been shown both in cadaver studies¹ and in vivo² to be largely equivalent in effectiveness and safety. More recently barbed suture has been shown to be safe for use in enteric closure although its widespread adoption has not yet occurred possibly due to current cost concerns.³ Although skin staples have been used for enteric closure in clinical studies in both dogs and cats^4,5 some concerns have been raised as to their ability to counteract physiological pressures during peristalsis in cadaveric models.

No matter which suture technique is used the critical component of any enteric closure pattern is that the submucosa, the holding layer of the gastrointestinal tract, be incorporated in the closure. For small intestinal resection specifically, new data has recently been published documenting improved outcomes with surgical stapling compared to hand-suturing in certain cohorts of patients.^6,7 These multi-institutional studies have shown statistically using much larger case cohorts that dehiscence rates may be decreased if surgical stapling is used especially in the presence of septic peritonitis.⁷ Generally a functional end-to-end anastomosis is created using a gastrointestinal anastomosis (GIA) stapler.

The ends of the two stapled segments of small intestine are then sealed with either a thoracoabdominal (TA) stapler or a second GIA cartridge.

These anastomoses are very rapid to perform but do add significant cost over hand-sutured techniques.

However, in the subgroup of dogs requiring GI resection in the face of peritonitis, this cost appears to be warranted. Surgical stapling however is not the only modality a surgeon can rely on as it really is only practical for GI resection in the jejunum and ascending duodenum as the large ends of the GIA forks need to be able to be passed through the lumen of adjacent segments of intestine. This requires significant mobility of the bowel segments involved and makes it impossible in the descending duodenum, around the ileocecocolic valve and in the large intestine. It is also not practical in smaller breeds of dogs and cats using the most commonly used human GIA staplers (e.g., GIA stapler, Medtronic, Salem, MA).

The descending duodenum is an unusual site for surgical lesions to occur with the possible exception of ulcers associated with NSAID and/or steroid use, renal disease or other conditions. In these dogs, a predilection site for the upper descending duodenum appears to be present although these lesions seem to be getting less commonplace with a better understanding by veterinarians and owners on the use of sensible prescribing habits and the avoidance of co-administration of these different groups of drugs. In the case of a perforating ulcer in the proximal descending duodenum a local resection of the ulcer bed can be performed with a transverse closure in order to minimize the risk of luminal narrowing if the lesion is modestly sized. With more extensive ulcers or masses in this area, care should be taken to visualize the common bile duct as if resection of this structure or the major duodenal papilla is deemed necessary biliary rerouting will need to be performed.

Knowledge of factors that adversely affect healing of the large intestine should be considered prior to undertaking large intestinal resections. The large intestine has a much greater anaerobic bacterial load compared to the small intestine. The large bowel heals more slowly and may in the case of large resections (such as those performed during subtotal colectomy for feline megacolon) be exposed to significant tension. Additionally, the blood supply to the lower colon may not be as robust as that of other areas of the bowel making preservation of the caudal rectal artery important when performing resections in this area. Indications for large intestinal resection are principally for management of megacolon, resection of neoplastic lesions and rarely mesenteric volvulus involving the large intestine.

Colotomy for foreign body removal is generally not indicated and neither are full-thickness biopsies of the colon as colonoscopic biopsies usually suffice for diagnosis of inflammatory conditions of the large intestine. Large intestinal closure is performed by this author in the same way as for small intestine with a single layer appositional suture pattern although some surgeons prefer a two-layer closure for large intestine, especially in large-breed dogs.

References

1.  Kieves NR, Krebs AI, Zellner EM: A Comparison of ex vivo leak pressures for four enterotomy closures in a canine model. J Am Anim Hosp Assoc 2018;54:71–76.

2.  Weisman DL, Smeak DD, Birchard SJ et al: Comparison of a continuous suture pattern with a simple interrupted pattern for enteric closure in dogs and cats: 83 cases (1991–1997). J Am Vet Med Assoc 1999;214:1507–1510.

3.  Ehrhart NP, Kaminskaya K, Miller JA: In vivo assessment of absorbable knotless barbed suture for single layer gastrotomy and enterotomy closure. Vet Surg 2013;42:210–216.

4.  Schwartz Z, Coolman BR: Closure of gastrointestinal incisions using skin staples alone and in combination with suture in 29 cats. J Small Anim Pract 2018;59:281–285

5.  Schwartz Z, Coolman BR: Disposable skin staplers for closure of linear gastrointestinal incisions in dogs. Vet Surg 2018;47:285–292

6.  Duell JR, Thieman Mankin KM, Rochat MS et al: Frequency of dehiscence in hand-sutured and stapled intestinal anastomoses in dogs. Vet Surg 2016;45:100–103

7.  Davis DJ, Demianiuk RM, Musser J et al: Influence of preoperative septic peritonitis and anastomotic technique on the dehiscence of enterectomy sites in dogs: A retrospective review of 210 anastomoses. Vet Surg 2018;47:125–129.