Cet article scientifique rend compte d'une polémique entre un spécialiste américain, qui définit et documente les aspects et problèmes éthiques concernant les prélèvements "à coeur arrêté", et un spécialiste canadien, qui a mis en place les protocoles des prélèvements "à coeur arrêté" au Canada. Le terme anglo saxon correspondant à "prélèvements 'à coeur arrêté'" est "Donation under Cardiac Death" (DCD). Cette polémique est éclairante pour la situation française, même si les protocoles de prélèvement "à coeur arrêté" appliqués en France depuis 2007 sont différents de ceux appliqués aux USA et au Canada. On pourrait d'ailleurs argumenter pour répondre à la question de savoir si cette différence est plus une différence de fond ou de forme ...
Qu'est ce qu'un prélèvement "à coeur arrêté" ? Lire l'article sur Wikipedia.
Friday, April 02, 2010 - Elsevier Global Medical News. By Joseph L. Verheijde, Ph.D., and Samuel D. Shemie, M.D.: Circulatory standard is full of scientific flaws.
VERSION FRANCAISE
"The growing demand for transplantable organs has refocused attention on a circulatory standard of death." [En France : on parle de prélèvements "à coeur arrêté", qui ont repris depuis 2007. Avant 2007, seuls les patients en état de "mort encéphalique" pouvaient constituer de potentiels donneurs d'organes. Leur cerveau est détruit mais leur coeur bat encore pour quelques heures. A présent, les prélèvements "à coeur arrêté" posent le problème inverse : la fonction cardiaque ne peut plus être restaurée. La question est : à quel moment exactement le cerveau est-il détruit dans cette situation ? Rappelons que les critères traditionnels de la mort impliquent la destruction du coeur, du cerveau et des poumons. Ndlr.]
"Cardiac mechanical asystole (or absent arterial pulse) lasting anywhere from 75 seconds to 5 minutes is the U.S. circulatory standard of declaring death in donation after cardiac death (JAMA 2009;301:1902-8). At that point, mechanical ventilation and hemodynamic support are both discontinued in the operating room, and surgical procurement begins after an absent arterial pulse or mechanical contraction of the heart.
However, there are a range of scientific flaws in the current circulatory standard of death used for organ donation.
First, it is based on expert opinion of a zero chance of spontaneous recovery of heart and brain functions (autoresuscitation) after 65 seconds of mechanical asystole. Scientific evidence is based on observations or 'death watch' inferred from published case series (1912 and 1970) and one retrospective study of 12 patients in non-heart-beating donation (Crit. Care Med. 2000;28:1709-12; Philos. Ethics Humanit. Med. 2007;2:28). The sample size necessary to rule out any autoresuscitation after 65 seconds in less than 1 in 1,000 donors with a reasonable scientific certainty is more than 10,000 patients.
Second, procured hearts have normal native mechanical and electrical functions after transplantation (N. Engl. J. Med. 2008;359:709-14; Eur. J. Cardiothorac. Surg. 2010;37:74-9), demonstrating that mechanical asystole is reversible and does not constitute an acceptable standard for irreversibility.
For example, when artificial circulation is restarted with cardiopulmonary bypass for preserving organs (ASAIO J. 2006;52:119-22), donors with normal brains before mechanical asystole can recover neurological functions. Several preprocurement donor interventions performed for organ preservation (Surgery 2000;128:579-88) likely preserve or prevent rapid deterioration of neuronal viability and irreversible cessation of brain functions after mechanical asystole. [C'est aussi ce qui s'est passé en France, voir ce cas de 2008 relayé par la presse : "Le donneur n'était pas mort !" (juin 2008). Ndlr.]
Third, the extent of recovery of integrated brain functions during surgical procurement is unknown. A preliminary report of electroencephalogram recordings during the dying process indicate sharp increases in brain electric activities in pulseless patients for several minutes (J. Palliat. Med. 2009;12:1095-100). Such patients can be donors undergoing surgical extraction of organs without general anesthesia (Anesth. Analg. 2010 March 17 [doi:10.1213/ANE.0b013e3181d27067]).
No neurophysiological monitoring studies of donor brains have been done to exclude residual and clinically relevant pain or awareness during surgical procurement.
Neither are there any histopathological examinations of brains from donation after cardiac death (DCD) donors that validate the claim that 2-5 minutes of mechanical asystole will inevitably result in complete destruction or necrosis of the whole brain and irreversible cessation of neurological functions (Crit. Care Med. 2010;38:963-70; J. Clin. Ethics. 2006;17:122-32). [La question reste donc intacte : le cerveau du donneur "mort", dont les organes sont prélevés "à coeur arrêté", est-il détruit au préalable du prélèvement d'organes ? Ndlr.]
In an article on organ donors after circulatory determination of death, the authors concede that donors may not necessarily be dead, either by neurological or circulatory criteria, but that 'it does not really matter' (Crit. Care Med. 2010;38:1011-2). They assert that any residual neurological functions have 'nothing to do with a person being alive in any meaningful way.'
However, that raises the questions of how and by whose standards the term 'meaningful' is to be defined and how certain neurological functions should be quantified as meaningful in another human being. Advocates consider altruism a sufficient reason for donors to endure this harm, if necessary, because of the desire to donate organs of the highest quality.
Transplantation advocates reinterpret the U.S. Uniform Determination of Death Act of 1981, which defined death as a singular phenomenon by either irreversible cessation of circulatory and respiratory functions or of all brain and brainstem functions, to mean that determining death can also be based on intent and action not to resuscitate, and therefore brain, respiratory, and circulatory functions do not necessarily need to have ceased irreversibly.
This reinterpretation masks undisclosed intent (to recover transplantable organs) and action (to begin surgical procurement before legal death) from the general public.
Procuring transplantable organs then becomes an active intervention of ending a human life, bringing up the ethical and legal questions of whether this approach requires sanctioning utilitarian homicide, transgressing on individuals’ constitutional rights, and disclosing relevant scientific information to potential donors and surrogates?"
Dr. Verheijde is an associate professor in the departments of biomedical ethics, physical medicine, and rehabilitation at the Mayo Clinic in Arizona. Some of the materials discussed here will also appear in Critical Care Medicine as a Letter to the Editor in response to a paper coauthored by Dr. Shemie (Crit. Care Med. 2010 March 11 [doi:10.1097/CCM.0b013e3181d8caaa]). He has no relevant disclosures.
"Laws on consent define notion of irreversibility.
The transition from life to death is a complex process fraught with historical, philosophical, and religious debate.
The determination of death affects all physicians regardless of specialty, and modern, sophisticated medical technology has complicated this process. The availability of life-sustaining interventions such as cardiopulmonary resuscitation (CPR), mechanical ventilation, heart-lung support machines, ventricular assist devices, and other organ replacement technologies, including transplantation, has obscured our ability to distinguish between the seemingly discrete states of life and death.
The ethical norm for organ donation is the 'dead donor rule,' which states that living patients must not be killed by organ retrieval. For transplantation to be successful, the arrest of circulation and resulting warm ischemic injury must be minimized. This is partially overcome when death is determined using neurological criteria because the brain dead donor remains on a ventilator and circulation persists until surgical removal of organs.
Brain dead donors continue to be the preferred source of transplantable organs, however, in response to the persistent shortage of organs has been the re-emergence of donation after cardiac death (DCD). DCD programs have developed throughout the world and account for the largest incremental increase in organ donation in active U.S. programs. Accompanying this renewed emphasis on DCD is the requirement to determine death as rapidly as possible following cardiac arrest, to minimize ischemic organ injury. This time pressure has forced the identification of a precise waiting period that is long enough to ensure the donor has died, yet short enough to maintain organ viability for transplantation.
Death is generally understood to be based on the irreversible cessation of either brain or circulatory/respiratory functions. The language and notion of irreversibility is problematic and the U.S. Uniform Determination of Death Act did not define the term. Its meaning and interpretation has evolved, given the profound advances in the technical ability to sustain vital functions indefinitely. Almost uniformly, hospital deaths are preceded by a decision to forego some form of life-sustaining intervention. If your heart is arrested, you are not dead unless CPR or extracorporeal life support is terminated or not initiated. Even in brain death, the notion of irreversibility can be questioned, given the theoretical availability of decompressive craniectomies to prevent the pressure-related arrest of brain blood flow in refractory intracranial hypertension.
Does 'irreversible' mean 'cannot be reversed under any circumstances' or 'will not be reversed,' consistent with appropriate care?
Outside of organ donation, determining death after cardiac arrest has not included standardized diagnostic criteria or a specific time period of observation. DCD has enhanced the rigor of the determination of death after cardiac arrest. However, there is a lack of consensus on how long circulation must cease for a person to be determined dead. Internationally, this time period varies from 75 seconds to 10 minutes.
After circulatory arrest in humans and primates, it takes less than 20 seconds for the EEG to become isoelectric. As long as the circulatory arrest remains permanent, there is a complete arrest of brain function. In this way, cardiac death and brain death are similar. Both are associated with the absence of brain blood flow – no blood flow, no neurological function. Cardiac arrest does not lead to death because if the heart stops, the heart can be artificially restarted, replaced by a machine that provides circulation, and/or replaced by transplantation. Cardiac arrest is death principally when it leads to a permanent arrest of brain blood flow.
Irreversibility of circulation after cardiac arrest thus is defined as a state in which these functions cannot return on their own and will not be restored by medical interventions. This applies to the setting of a legally valid refusal of CPR by the patient directly, through advance directive or via the patient’s substitute decision maker. In this way, irreversible is defined as not physically possible to reverse without violating the law on consent.
Although autoresuscitation, a phenomenon of the heart being able to restart spontaneously and generate circulation, has been cited as an ethical concern, the existing literature in this regard is of extremely poor quality. In our recent systematic review of autoresucitation (Crit. Care Med. 2010 March 11 [doi:10.1097/CCM.0b013e3181d8caaa]), there are no cases described in which CPR was not provided. Thus the existing practices for determining death during controlled DCD, where a consensual decision has been made to withdraw life support and withhold CPR, are consistent with medical, ethical, and legal standards permitting organ donation."
Dr. Shemie is a pediatric critical care physician and director of the Extracorporeal Life Support program at the Montreal Children’s Hospital, McGill University; the Bertram Loeb Chair in Organ Donation Research at the University of Ottawa; and medical director of tissue and organ donation for the Canadian Blood Services.
Copyright (c) 2009 Elsevier Global Medical News. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
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