Richard Maundrell revisits the definition of death in light of new research suggesting the possibility of consciousness after a diagnosis of brain death.
In September 2017, a young Toronto woman, Taquisha McKitty, stopped breathing following an overdose of drugs. She was resuscitated by first responders, but it became apparent in the days that followed that she had suffered brain damage from lack of oxygen. The medical team treating her at Brampton Civic Hospital determined that she was brain dead and advised Taquisha’s family that it was time to remove her from life support. Taquisha’s family disagreed. They insisted that treatment be continued and mounted a legal challenge to Brampton Civic’s diagnosis of brain death. Taquisha’s heart failed the following February, before the case could be heard in court, but cases like hers raise difficult questions about how death should be defined.
It was in 1968 that an ad hoc committee of the Harvard University Medical School introduced the concept of brain death with proposed clinical guidelines for its application. The work of the committee had been motivated by the arrival of mechanically assisted ventilation technology during the 1950’s, which made it possible to sustain blood flow and circulation in a body that had lost the capacity for consciousness. In the years that followed, the concept of brain death, with some variation in diagnostic detail, became part of medical convention worldwide. But the concept continues to elicit ethical controversy.
Questions have persisted about the validity and reliability of the criteria used in diagnosing brain death, particularly in respect to the weight clinical guidelines place on testing for brainstem function. The brainstem, which sits atop the spinal cord, performs a critical role in maintaining and regulating the body’s circulatory and respiratory functions. It also plays a key role in triggering wakefulness and regulating the sleep/wake cycle, and thus is essential to maintaining consciousness. While it is not yet understood exactly which brain structures are involved in producing conscious thought and perception, the coordinated activity of various structures in the cerebral cortex (the convoluted outer layer of the brain) is generally thought to be the source of such phenomena. Clinical guidelines for the diagnosis of brain death based largely on the absence of brainstem reflexes assume that the loss of brainstem function would preclude consciousness even in cases where the cortex remains intact and sufficiently oxygenated. The lingering question – and the stuff of nightmares – is the possibility that this assumption is mistaken.
The fiftieth anniversary of the report of the Harvard committee has come and gone, but the debate continues with new impetus from developments in clinical neuroscience. In an article published in the November 2018 issue of Clinical Neurophysiology, the authors suggest that the brainstem can be damaged in a way satisfying clinical criteria for brain death while leaving the patient with the capacity for consciousness. Any cortical activity detected by EEG where brainstem reflexes are absent might, they argue, be “a surrogate marker of potential residual consciousness”. In a study of 296 subjects whose cortical activity was tracked using EEG following a diagnosis of brain death, cortical activity was present in 3.5% of cases. They argue that an ancillary test of cortical activity, such as EEG, should be a standard part of the procedure by which brain death is determined: a practice which is already a matter of protocol in some localities, and one which is recommended by the American Academy of Neurology.
Cortical activity as indicated by EEG, however, does not mean that consciousness is present and, to date, there is no reliable clinical test for consciousness. But the potential for consciousness has to be the crucial consideration in defining death, for nothing can “matter” except to a conscious being. Perhaps the best general definition of death is that which appears in the Academy of Medical Royal Colleges’ A Code of Practice of the Diagnosis and Confirmation of Death: “Death entails the irreversible loss of those essential characteristics which are necessary to the existence of a living human person and, thus, the definition of death should be regarded as the irreversible loss of the capacity for consciousness, combined with irreversible loss of the capacity to breathe”.
Developing a test that can reliably determine when consciousness has been irreversibly lost remains a large challenge for medical research and neuroscience. It is an issue which will likely become more complicated rather than less as we work toward an understanding of the neurology of consciousness. As the McKitty case highlights, we need a definition of death that will allow us to make appropriate decisions concerning the treatment of the brain-injured, but that definition needs to be informed by the developing science of consciousness.
Richard Maundrell is an Associate Professor in the Department of Philosophy at Lakehead University.