8. What are the main principles behind deceased organ donation?
Correct answer:
There are two types of organ donation from deceased donors: (1) donations after brain stem death and (2) donation after cardiac death (non-heart-beating donation). Most organs for transplantation come from donors who have sustained a lethal brain injury following a head injury, intracranial haemorrhage or primary brain tumour, and who have been certified dead by ‘brain stem’ criteria. The organs are removed from the donor in the operating theatre after isolating their vascular pedicles and while the heart is still beating; when circulation ceases the organs are rapidly cooled by perfusion in situ with an ice-cold organ-preservation solution. When patients have sustained a catastrophic brain injury, but do not fulfil the criteria for the diagnosis of death by brain stem criteria, the supervising doctors may nevertheless decide that future treatment is futile. In such circumstances life-supporting treatment is withdrawn and the patient dies, death being certified by the absence of a circulation. Following cardiac arrest the donor is transferred to the operating theatre, where the organs are rapidly cooled, perfused with preservation solution and removed. Unlike organs from brain dead donors, organs removed from donors after cardiac death suffer a period of warm ischaemia prior to cooling. During this period, the organs switch from aerobic to anaerobic metabolism, which depletes intracellular energy stores and causes the accumulation of lactic acid. Unchecked, this process rapidly results in cell death. Organs vary in their tolerance of warm ischaemia, with kidneys remaining viable for about 60 minutes whereas the liver tolerates less than 30 minutes. In such cases, the initial function of the organs is inferior to those removed following brain stem death, but the ultimate function is satisfactory.