Читать книгу Gastrointestinal Surgical Techniques in Small Animals - Группа авторов - Страница 26

The colon is considered by most surgeons as a rather “unforgiving” structure when it is incised and repaired, largely because of its unique healing qualities, and when leakage occurs, the results are often devastating to the animal (Williams 2012). An understanding of colonic healing is important, and incorporation of all the principles of repair are critical to reduce life‐threatening anastomotic dehiscence. Healing of the colon undergoes similar phases of wound healing to those found in the skin and other tissue layers but with a number of important differences (Agren et al. 2006). During the inflammatory phase, a fibrin clot forms over the site and, although this clot has minimal strength, it is important to achieve an early “seal,” and it is vital that it remains to act as a scaffold for fibroblast migration during the early repair phase. For the first three to four days, nearly all support for the colonic repair comes from the suture or staple line. Angiogenesis and migration of fibroblasts occurs and eventually replaces the fibrin clot scaffold during days 3 and 4. It is during this stage of repair that breakdown is most likely to occur (Williams 2012).

Although a fragile mucosal bridge also occurs within the first three to four days, depending on the size of the defect, substantive wound strength occurs only when local recruited smooth muscle cells and fibroblasts from the colonic submucosa and muscularis bridge the incision and begin producing collagen. Appropriate‐sized tissue bites are particularly important when repairing the colon because a zone of active collagen lysis occurs in a 1–3 mm zone immediately adjacent to the incised colon edge. The activity of matrix metalloproteases that cause collagen degradation peaks during the debridement phase through day 3 (Agren et al. 2006). Provided there is ample vascular supply after this time, collagen synthesis is accelerated, coupled with a rapid gain in wound strength. Aggressive tissue handling and excess contamination of the colonic wound can greatly increase the debridement activity at the sutured wound edge and this increases the risk of early tissue disruption, leading to dehiscence and leakage (Williams 2012). Return of strength at the healing site reaches about 75% of normal strength at four months after surgery, which is considerably slower than in the small intestine (Thornton and Barbul 1997). Surgeons can influence uncomplicated colonic healing by ensuring adequate tissue perfusion, eliminating any tension on the repair, accurately apposing colonic edges without inducing excess trauma, containing contamination, and avoiding increased intraluminal pressures by eliminating any distal obstruction (Holt and Brockman 2003; Williams 2012). Omental pedicle wraps have been advocated to reinforce the gastrointestinal repairs and support the local healing environment. Omentum may stimulate and augment angiogenesis and may also help maintain the vital fibrin clot and seal during the early phases of wound healing. The benefit of omental wraps in colonic surgery have not been proven in recent human clinical studies of colonic resection and anastomosis. However, most surgeons still recommend covering colonic repairs with omentum (Hao et al. 2008).