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PATHOPHYSIOLOGIC CONSIDERATIONS IN DBD DONORS

  • Cerebral swelling after brain injury is a common phenomenon.

  • The fixed volume of the human skull results in increased intracranial pressure.

  • Brain perfusion=function of mean arterial pressure minus intracranial pressure.

    • Increase of intracranial pressure has to be accompanied by an increase of mean arterial pressure to preserve brain perfusion.

    • The brainstem contains baroreceptors issuing activation of the autonomic nervous system and releasing catecholamines.

    • During cerebral swelling and brain death, catecholamine levels can be observed up to 20-fold of normal values.

    • Consequently, such a catecholamine storm leads to:

      • Dramatically increased systemic blood pressure

      • Subintimal hemorrhage in the arteries (particularly at bifurcations) with a risk of thrombosis

      • Microcirculatory perfusion defects due to increased macrovascular tension

  • Brain herniation and coning lead to:

    • Hypotension and vasodilation

    • Failure of hormonal and neural regulators of vascular tone

      • Cessation of antidiuretic hormone (ADH) secretion (diabetes insipidus and hypernatremia)

      • Failure of the hypothalamic-pituitary axis (steroids, thyroid hormones, etc.)

GRAFT SUITABILITY

Physical graft characteristics:

  • Organ dimensions correlate with donor body weight and height.

  • Transplanted liver mass needs to be sufficient for the demands of the recipient

  • Liver mass of donor organ can be estimated by estimated standard liver weight formulas.1

  • Estimated liver mass needs to be fitted to the allograft body weight ratio2 (minimal graft body weight ratio [GBWR] of 0.8%, optimal GBWR >1%).3

  • Recipient’s abdominal cavity dimensions define transplantable organ dimensions.

    • Large organs:

      • Increase intraabdominal pressure after abdominal closure

      • Large-for-size situation (insufficient perfusion)

      • Estimate: donor body weight 20 kg higher than recipient is acceptable.

    • Small organs:

      • Suitable as long as GBWR seems suitable, with some groups reporting favorable results with GBWR <0.8% in living donor liver transplantation.4,5

The general characteristics of the donor influencing the “donor quality” need to be delineated from characteristics of the donor liver influencing the “organ quality.”

DONOR QUALITY

Factors directly associated with the donor or to the conditions or circumstances of becoming an organ donor have been defined by several studies, but are not always comprehensive.

Donor Age

  • Consent exists that donor age is an independent risk factor for graft survival.

  • Older donors carry the pronounced risk of developing early allograft dysfunction and are more susceptible to ischemia-reperfusion injury.

  • No definite upper age threshold exists.

  • Case series utilizing septuagenarian or octogenarian donors with excellent results have been published.6,7

  • In our experience, the biological age of the donor is far more important but can be hard to assess.

  • The lower age threshold for pediatric donor livers remains undefined.

  • Pediatric donor organs are usually of optimal quality. If not transplanted into pediatric recipients, suitability for allocation to adult recipients is usually given as long as a suitable GBWR exists.8

  • Donor age is used for the calculation of the liver donor risk index.9

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