12 Transplant surgery
Introduction and definitions
• Cadaveric donors who are brainstem dead are the commonest source of organs, often following severe head injury. The procedure for confirming brainstem death requires two senior doctors to perform a series of tests to establish the diagnosis (Box 12.1).
• Cadaveric non-heart-beating donors are occasionally used for renal transplants.
• Live donors may be related or non-related to the recipient. Living donors are usually first degree relatives of the recipient. Unrelated donors are rare in the developed world, though trading in organs occurs in poor countries.
• Autograft: transplantation of an organ from one part of the body to another part of the same individual.
• Isograft: transplantation of tissue between genetically identical individuals, i.e. identical twins.
• Allograft: transplantation of tissue from an individual of the same species. Most human organ transplants are allografts.
• Xenograft: transplantation of tissue from one species to another. This is limited to avascular tissues that have been treated to remove antigens. Porcine heart valves are examples of such grafts. Larger organs are rejected immediately. Using animal organs for human transplants would solve the organ shortage problem but there remain serious difficulties related to rejection and the potential for transfer of infectious diseases from the animal to human population.
• Orthoptic graft: the donor organ is transplanted to the same site after removal of the recipient’s diseased organ, e.g. liver transplantation.
• Heterotopic graft: the organ is grafted to a site remote from the normal anatomic position, e.g. renal transplantation to the iliac fossa.
Box 12.1
Defining brain-stem death
3 Absent oculo-vestibular reflexes
4 No response to supraorbital pressure
5 No cough reflex or gagging response
6 No observed respiratory effort in response to disconnection of the ventilator (such that CO2 >6 kpa)
(from Academy of Medical Royal Colleges 2008 A Code of Practice for the Diagnosis and Confirmation of Death)
Rejection
• Hyperacute rejection is caused by preformed circulating antibodies present in the recipient’s blood which recognise antigens present on the cells of the donor organ. Rejection begins within hours and immediate loss of the graft ensues.
• Acute rejection is cell mediated and usually occurs 5–14 days after transplantation, though sometimes it may take several months.
• Chronic rejection involves cell- and antibody-mediated processes and causes graft ischaemia. Deterioration is slow and insidious but inevitably results in graft failure.
Matching donor to recipient
Tissue typing
The molecules that are involved in immune recognition are the major histocompatibility (MHC) antigens. Class I MHC antigens are expressed as integral proteins of the surface membranes of all nucleated cells and platelets. Class II MHC antigens are found on lymphocytes. The genes coding for the MHC proteins are located on the short arm of chromosome 6, termed the human leucocyte antigen (HLA) loci (Table 12.1). Tissue typing identifies which of the HLA-A, -B and -DR alleles are present for a donor or recipient.
Table 12.1 The four HLA loci and their importance in organ transplantation. Modern immunosuppressants have made HLA compatibility less critical
| HLA locus | Number of alleles identified/function |
|---|---|
| HLA-A | 20 alleles |
