Small Bowel Transplantation
Progress in small bowel transplantation has lagged well behind that of other types of solid organ transplantation. Intestinal transplants stimulate a particularly strong graft rejection response, probably because the small intestine contains very large amounts of lymphoid tissue. Moreover, ischaemia and rejection increase intestinal permeability and allow translocaton of bacteria from the lumen of the bowel. Added to this, the operation is often complex and made technically difficult because of repeated previous abdominal surgery. Consequently, graft rejection and infection remain a major problem after small bowel transplantation and the results obtained are inferior to those seen after other types of organ transplantation. Small bowel transplantation is a treatment option for patients with intestinal failure as defined by the loss of intestinal function to the extent that long-term parenteral nutrition is required. Intestinal failure may result from short bowel syndrome after resection of the intestine or from intestinal dysfunction. The conditions that may give rise to intestinal failure include the following:
• intestinal atresia;
• necrotising enterocolitis;
• disorders of motility;
• mesenteric infarction;
• Crohn’s disease;
• desmoid tumours.
Because of the substantial risks associated with small bowel transplantation, the procedure should be considered only for those patients where long-term total parenteral nutrition (TPN) has failed, usually because venous access has become impracticable or because of frequent life-threatening line sepsis. The need for small bowel transplantation is estimated at around 0.5—1.0 patients per million population and around 50 per cent of cases are children.
Small bowel transplantation may be carried out as an isolated procedure, performed together with a liver transplant or undertaken as a component of a multivisceral transplant. Around half of all small bowel transplants are performed in children. Where possible, isolated small bowel transplantation is undertaken because patient survival is higher.
A small bowel transplant from a cadaveric donor comprises the entire small bowel but it is no longer considered advisable to include the ascending colon in the graft. The superior mesenteric artery of the graft (with an aortic patch is anastomosed to the recipient aorta and the superior mesenteric vein is anastomosed to the inferior vena cava or to the side of the portal vein. The proximal end of the small bowel graft is anastomosed to the recipient jejunum or duodenum. The distal end of the graft is anastomosed to the side
of the colon (with a loop ileostomy) or is fashioned as an end ileostomy. A gastrostomy tube (to overcome delayed gastric emptying) and a feeding jejunostomy tube are inserted.
About half of all patients who require small bowel transplantation have cholestatic liver disease secondary to TPN and require combined liver and small bowel transplantation. Cholestatic liver disease due to TPN is especially common in children. When combined liver and small bowel transplantation is carried out the two grafts are transplanted en bloc. The donor aorta is fashioned into a conduit including the superior mesenteric and coeliac arteries, and anastomosed to the recipient aorta. The portal vein anastomosis is as for isolated liver transplantation.
Multivisceral or ‘cluster’ transplants may be necessary in the case of large desmoid tumours where excision of both the small bowel and adjacent organs is required, when there has been extensive thrombosis of the splanchnic vessels and for generalised disorders of gastrointestinal motility.
The 1-year graft survival rate after small bowel transplantation is about 60 per cent for both isolated small bowel transplantation and combined liver and small bowel transplantation. After 3 years the graft survival rate is around 40 per cent. As already noted, however, patient survival is better after isolated small bowel transplantation than after combined liver and small bowel transplantation, where loss of the graft usually equates with death of the recipient. Most of the mortality after small bowel transplantation is due to sepsis and multiorgan failure. The risk of infection after small bowel transplantation is heightened by the additional requirements for immunosuppression in order to control graft rejection. This accounts for the relatively high incidence of lymphoproliferative disease (around 10 per cent) observed in patients who have undergone small bowel transplantation. Because of the large amount of donor lymphoid tissue transplanted graft-versus-host disease (GVHD) may occasionally be an added complication. Despite the hazards, small bowel transplantation offers patients with intestinal failure a chance to lead an active life free from the constraints of long-term nutritional support.
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