Intestinal Transplantation - pediagenosis
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Sunday, November 17, 2019

Intestinal Transplantation

Intestinal Transplantation
Types of transplant
There are three main types of intestinal transplantation performed. All involve transplanting a sufficient length of small intestine to achieve independence from parenteral nutrition (PN). The large intestine is not usually transplanted, although its inclusion has been proposed as a way to reduce fluid losses. The terminal ileum is brought out as an ileostomy to facilitate biopsy, although this may be reversed in the long term by anastomosis to the native colon (if still present) to restore gut continuity. Where there is pre-existing renal failure it is sensible to perform a kidney transplant at the same time.

Other operative combinations are possible (such as liver and small bowel alone), but the three below are the most common.

Intestinal Transplantation, Multivisceral transplant,

Multivisceral transplant
Where there is intestinal failure and severe associated liver disease, it is customary to perform a transplant that includes liver and small bowel; this is most easily accomplished by implanting a bloc of tissue (a cluster) which also includes the stomach, duodenum and pancreas, and which receives its arterial supply from the coeliac trunk and superior mesenteric artery (SMA), with venous drainage via the hepatic veins with the liver implanted either using the caval replacement or piggyback technique (see Chapter 35). The donor stomach is anastomosed to a cuff of recipient stomach just below the diaphragmatic hiatus.
The transplanted stomach is denervated, so the vagus nerve supply is absent, resulting in closure of the pylorus, which prevents gastric emptying. A gastric drainage procedure is therefore necessary, either a pyloroplasty or a gastroenterostomy.

Modified multivisceral transplant
Where the liver is minimally diseased with an anticipation of recovery, a transplant excluding liver is appropriate. If there has been previous gastric or pancreatic disease, such as PN-related pancreatitis, the bloc of tissue should include the stomach and duodenum, with the portal vein being anastomosed to the recipient portal vein at the hilum of the liver.

Small bowel alone
Isolated small bowel transplantation is the simplest procedure to undergo. The SMA is anastomosed to the aorta, the superior mesenteric vein (SMV) to the inferior vena cava (IVC); if the liver function is satisfactory there is no need for a portal venous anastomosis.
An isolated intestinal transplant has the additional advantage that, should serious complications occur, it can be readily removed and the patient returned to PN until fit for a retransplant.

Donor assessment
Since the majority of patients undergoing intestinal transplantation have had multiple bowel resections there is very little perito- neal cavity remaining (known as abdominal domain). Donor organs therefore need to be smaller than the recipient wherever possible, to enable closure of the abdomen.
Aside from the issues of size, the donor organs are generally best obtained from slim individuals with little mesenteric fat in order to facilitate rapid cooling on retrieval.

Operative issues
Anaesthetic concerns
1.    Volume replacement: requires at least one large-volume line.
2.    For veno-veno bypass where caval replacement or cross-clamping of the IVC is involved, a patient central vein above the diaphragm is necessary.
3. Reperfusion of multivisceral block can release a large volume of cold potassium-rich preservation solution, which precipitates cardiac arrest.
Surgical issues
1.   Abdominal domain: is there sufficient space in the abdomen to fit the new intestine/bloc of tissue? It is undesirable to leave the abdomen open, although sometimes necessary in small children.
2.  Arterial inflow to the graft is via an SMA anastomosis on to the infrarenal aorta in an isolated graft; for a multivisceral graft a conduit of donor aorta is used to take blood from the infrarenal aorta to the SMA and coeliac trunk. It is undesirable to clamp the aorta above the renal arteries because of the renal ischaemia this causes.
3.    A gastric drainage procedure, such as a pyloroplasty, is required when the stomach is part of the multivisceral bloc.
4.  Tolerance of the intestine to cold ischaemia is much more critical than that of the liver or kidney. It is desirable to reperfuse the intestinal bloc within 4 hours where possible, although inevitably this is a compromise between proximity of the donor and difficulties encountered during the operation to prepare the recipient to take the bloc, an operation that may take many hours.

Post-transplant complications
Peri-operative complications
1.   Thrombosis of arterial supply or venous drainage is a risk, because many of the recipients have lost their original bowel due to a procoagulant tendency. In some cases this will have been cured by replacement of the liver.
2.   Delayed resumption of normal bowel function is common. The stomach is the last organ to start to work, often taking more than 3 weeks before peristalsis starts and it empties. Nutrition during this time is achieved using a jejunostomy into the new bowel.

Transplantation related complications
1.  Rejection is more common than with other organs, hence enhanced immunosuppression is required. Typical presentations are with increased or decreased bowel activity, with sepsis a common feature. The latter is a consequence of rejection impairing the mucosal barrier and permitting translocation of bacteria. The result is a need to enhance immunosuppression in a septic patient.
2. Infection is common, and often associated with intestinal rejec- tion or intra-abdominal collections.
3. Renal impairment. Intestinal transplant recipients have the highest incidence of kidney failure of any non-renal transplant type. This is in part due to the high-volume fluid losses from the gut, as well as the nephrotoxic immunosuppression.
4.    Recurrent disease, such as Crohn’s disease, may occur.
5.  Graft versus host disease is more likely after a multivisceral transplant than other forms of solid organ transplant and tends to occur within the first 3 or 4 months. This is because of the large amount of lymphoid tissue (mesenteric lymph nodes and mucosaassociated lymphoid tissue) in the graft, particularly if the donor spleen has been transplanted, as used to occur in some centres in the US. Lymphocytes transplanted with the donor can ‘reject’ the recipient, rather than the other way around. Features include perfect function of the donor organs, but rash, impaired liver function (only if liver is not part of graft) and fever. It is fatal in a significant proportion of those affected.

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