4. LARGE BOWEL ANASTOMOSIS

Introduction

The technique and principles of a large bowel resection are similar to those of a small bowel anastomosis. You should remember that the colon (particularly the left side) does not have as good a blood supply as the small bowel and that there is greater risk of contamination of the peritoneum.

Modification of the basic techniques will be required for colo-rectal anastomosis (see appropriate section) but a colo-colic anastomosis can often be performed as for a small bowel anastomosis. This may be the case after a transverse colectomy or a left hemicolectomy.

1. Adequate exposure

For most colonic surgery a midline incision is recommended. This can readily be extended if greater access is required.

2. Assessment of the situation

The same series of questions that were posed in the previous section should again come to your mind :

• Is resection required?
  For example, in a case of inflamed diverticular disease, if there is no perforation then resection may be unnecessary (so probably was the laparotomy). In a case of an iatrogenic perforation with a colonoscope, primary repair may be possible.
  
  
• What is the extent of the resection required?
  For a carcinoma this will be determined by the lymph node drainage and the pattern of the vascular supply. For a lesion in the transverse colon it may be that an extended right hemicolectomy is safer option than a transverse colectomy. Similarly, the distal sigmoid colon is not recommended for anastomosis (due to probable diverticular changes) and a colorectal anastomosis is preferred after a sigmoid colectomy. In resection for colorectal cancer or polyps, always remember to examine the large bowel carefully for a second (synchronous) tumour or polyp.
  
  
• Is an anastomosis wise?
  As stated above, the blood supply to the colon is not generally as good as to the small bowel. Therefore, in an emergency setting with unprepared bowel it may be wiser to think about a colostomy rather than an anastomosis. Certainly, in cases of sepsis most surgeons would avoid primary left-sided colonic anastomoses, although in patients who are in good condition and have an obstruction, the case for on-table lavage and anastomosis should be considered.
  
  
• Do I need help?
  You should be able to answer this one - but if in doubt ask.
  

3. Preparation of the bowel for anastomosis

Adequate mobilisation prior to your anastomosis becomes more of a problem when considering large bowel rather than small bowel resections. If a transverse colectomy is being considered (an uncommon procedure) you will have to mobilise both hepatic and splenic flexures. For a sigmoid colectomy, the splenic flexure should be mobilised so that the transverse colon can be potentially brought down for the anastomosis.

Pay particular attention to the vascularity of the colonic resection margins, ensuring that they are viable. The blood supply of the colon is not as rich as that of the small bowel and this is particularly the case with the left side of the colon

The other problem with colonic surgery is the potential for contamination of the peritoneal cavity. To counteract this, preparation should start, if possible, pre-operatively with mechanical bowel preparation. The wound edges should be protected, and, prior to resecting the colon, the bowel ends should be isolated with antiseptic-soaked swabs. The use of soft non-crushing clamps may also be considered.

4. Set-up of anastomotic site

In many colonic anastomoses you will have difficulty in bringing the ends to the surface of the wound. In such cases a technique as described later for an anterior resection may be used. Otherwise, set up as for a small bowel resection.

5. Technique

In cases where the bowel ends can be brought out onto the surface and rotated, the technique is very similar to that described in the small bowel section with an inverting sero-submucosal technique. Some surgeons find that, with the larger diameter of bowel to be joined, suture placement is helped by placing the mesenteric and anti-mesenteric sutures followed by a suture at the mid-point, thus dividing the anastomosis into four, shorter but equal lengths and thereafter placing sutures equidistant.