Pathophysiology of brain death: effects on allograft function

Update on donor assessment, resuscitation, and acceptance criteria, including novel techniques--non-heart-beating donor lung retrieval and ex vivo donor lung perfusion

The shortage of adequate organ donors remains a great challenge in clinical lung transplantation. With increasing experience in the medical management and surgical technique of lung transplantation, gradual expansion of the criteria for lung donor selection has occurred with beneficial effects on the donor pool. Interest in donation after cardiac death also is increasing as the gap increases between donors and the needs of listed patients. Successful use of these new sources of lungs depends on the accurate assessment and prediction of transplanted lung function. Promising techniques for lung assessment and diagnostics include investigating key genes associated with graft failure or good graft performance using molecular approaches, and ex vivo evaluation. Further studies are needed to answer remaining questions about the best technique and solution to reperfuse human lungs for several hours without edema formation. As the predictive ability to discern good from injured donor lungs improves, strategies to repair donor lungs become increasingly important. Prolonged normothermic EVLP seems to be a platform on which many reparative strategies can be realized. With these new methods for assessing and resuscitating lungs accurately, it is hoped that inroads will be made toward providing every listed patient a chance for successful lung transplantation.

Brain Death and Organ Procurement

Patients with severe brain injuries (as can result from trauma, subarachnoid hemorrhage, or brain tumor) are monitored closely by nursing staff. It's often the nurse who first recognizes clinical signs of decompensation and begins the process of determining whether the patient is a potential organ donor. When a person is declared brain dead, it's the nurse who maintains hemodynamic stability so that donor organs remain viable. It's therefore crucial for nurses to know how brain death is determined in adults and how potential organ donors are identified, and to know the major physiologic changes that occur upon brain death, as well as essential nursing interventions.

Clinical Management of the Organ Donor

There is a critical mismatch between available organs for transplant and acutely or critically ill patients with end-stage organ disease. Patients who may benefit from organ transplantation far outnumber available organs. The causes for this imbalance are multiple. One cause is family refusal to donate. A second cause is nonrecognition or delay in determination of brain death. A third cause is donor loss due to profound cardiopulmonary and metabolic instability consequent to brain-stem herniation and brain death. Family refusal may be addressed by education, public awareness, as well as close attention to social, cultural and ethical issues, and optimal communication with donor families. Brain death may be consequent to traumatic brain injury, ischemic versus hemorrhagic stroke, as well as massive cerebral anoxia/ischemic following cardiac arrest. Nonrecognition or delay in brain death determination may be addressed by clinician education and frequent clinical assessment to detect early stages of brain-stem herniation refractory to aggressive measures for control of intracranial pressure. Donor loss due to profound cardiopulmonary and metabolic instability may be addressed by aggressive, mechanism-based treatment for clinical instability based on affected body system, as well as measures to support metabolic activity at the cellular and tissue level in the brain-dead organ donor. This article explores cerebral physiology related to impending brain death and catastrophic intracranial pressure elevations. In addition, physiologic consequences of brain death are correlated with affected body systems and mechanism-based therapies to support organ function pending transplantation. Ethical/legal issues are explored as related to patient autonomy and optimal family outcomes. Effective family communication, astute clinical assessment, and optimal clinical management of the organ donor are illustrated using a case study approach, highlighting the role of the advanced practice nurse in donor management.

Hemoadsorption to Improve Organ Recovery from Brain-Dead Organ Donors: A Novel Therapy for a Novel Indication?

While brain-dead organ donors represent the majority of the organ donor pool, it appears that graft survival is adversely affected by brain death itself. Brain death has been shown to cause severe disturbances in the hormonal, hemodynamic and immunological homeostasis, which could in part be responsible for the inferior outcome of organs originating from brain-dead donors compared to living donors. Hemodynamic effects of brain death lead to a wide fluctuation in mean perfusion pressures, blood flow to the organs and systemic oxygen consumption, altering regional perfusion. In addition, a wide array of immunological changes has been shown to occur after brain death contributing to organ injury and hemodynamic instability. Recent studies have shown that brain death upregulates multiple lymphocyte- and macrophage-derived cytokines and the injured brain itself may be the source of proinflammatory factors such as S100B. This increased inflammatory response seen during and immediately after brain death has also been associated with poor allograft function. Furthermore, there is evidence to suggest that the massive inflammatory response seen in brain-dead donors could also lead to increased immunogenicity and accelerated allograft rejection after transplantation. Hence, we hypothesize that nonspecific downregulation of this inflammatory response by hemoadsorption could potentially lead to improved donor organ and allograft function. As a 'proof of concept' we tested the ability of a novel hemoadsorbent to remove S100B in vitro using two human glioblastoma cell lines. Our results indicate a >80% reduction in S100B after 2 h of circulation with the sorbent.