Patients diagnosed as being in a persistent vegetative state have figured prominently in the law and medical ethics relating to end-of-life decisions since the case of Karen Quinlan in 1976. These patients have profound brain injuries that leave them in the seemingly anomalous condition of being awake but not aware. They have normal sleep-wake cycles and the capacity to breathe on their own, but lack clinical signs of consciousness. Recent scientific developments that suggest signs of willful modulation of mental activity have roiled the waters relating to the care of patients in a vegetative state.
On November 10 The Lancet published a report that showed that EEG detected brain activation in a proportion of patients considered to be permanently unconscious. When asked to imagine making a fist or wiggling their toes in response to hearing a beep, these patients displayed brain activation comparable to that of healthy volunteers given the same task.
This result adds to earlier evidence (here and here) from functional magnetic resonance imaging (fMRI) that found that some patients considered vegetative showed brain activation identical to healthy volunteers when asked to imagine engaging in tasks such as playing tennis, moving around a room in their homes, or responding to a question. Studies on a limited number of patients diagnosed as being in a persistent vegetative state have found that between 10 percent and 20 percent of them show brain activation indicative of consciousness on either fMRI or EEG. Although the meaning of the studies is not without controversy, it seems reasonable to interpret them as demonstrating consciousness in some of patients considered vegetative based on expert clinical examination.
The EEG findings have immediate clinical implications. Unlike fMRI, which is a research tool not readily available in clinical settings, EEG can be brought to the bedside, is much less expensive, and is minimally intrusive.
In response to this stunning development questions need to be posed and pondered relating to three issues: (1) further testing and refinement of the potential for EEG to probe consciousness in vegetative patients, as well as other patients with related profound brain disorders; (2) technological ways to communicate with these patients to enhance their quality of life; and (3) end-of-life decision-making.
The expansion of scientific knowledge often opens up new areas of uncertainty. Clearly, the validity of EEG to detect consciousness needs to be confirmed by further research. As is the case with any diagnostic technology, there is a risk of false positives and false negatives: some patients thought to be conscious may be exhibiting only unconscious brain activity; others may be conscious even if they do not display signs of consciousness on EEG. But they might be judged conscious if tested with fMRI or some new technology.
Beyond diagnosis lie important questions about whether and how EEG can be used to communicate with seemingly vegetative patients. In addressing this issue we are not completely in the dark. The analogous situation of patients in a locked-in state, with intact consciousness and the ability to communicate via blinking an eye, deserves attention.
These patients can communicate their quality of life and autonomous preferences for treatment without speech or conventional sign language. A key difference, however, is that with locked-in patients, clinicians and family members can readily interpret the meaning of eye blinks, as is so vividly represented in the remarkable book, The Diving Bell and the Butterfly, composed and dictated by Jean-Dominique Bauby while in a locked-in state. But interpretation of signals recorded by EEG or fMRI is more open to question, especially in the early stages of scientific investigation and clinical applications. Uncertainly about interpretation of brain signals might be mitigated in the future if it is possible for patients to respond to questions and initiate communication with the aid of computer technology.
The potential to communicate with patients who have no clinically detectable signs of consciousness raises a host of questions about understanding and enhancing their quality of life. Are they in pain? How can pain be assessed? If they are in pain, can it be relieved without sedation diminishing or extinguishing consciousness? Does a patient want to be wheeled outdoors or listen to music? And, more generally, what are these patients entitled to receive to optimize their quality of life?
Clearly, if EEG is eventually used routinely to assess consciousness for patients who appear to be vegetative, we need to explore the implications for end-of-life decisions. For patients without any signs of consciousness, there is no reason to change end-of-life decision-making approaches. While the possibility of a false negative diagnosis of lack of consciousness cannot be ruled out, it should still be up to surrogate decision-makers, in consultation with clinicians, to determine whether to continue life-sustaining treatment, based on the prior preferences and values of the patient, if known, or what they judge to be in the patient’s best interest.
A major challenge concerns those patients who are able to respond to commands and questions by means of EEG. How will their decision-making capacity be assessed? How can we be confident that technologically-mediated communication with these patients can represent their autonomous choices in making fateful decisions about whether to continue living or to stop life-sustaining treatment?
As we reflect on the latest research in this domain and its implications at the bedside, we should also ponder with fascination and humility how science transforms and complicates medical ethics.
Franklin G. Miller, Ph.D., is a member of the senior faculty in the Department of Bioethics, National Institutes of Health. Robert D. Truog, M.D., is a professor of medical ethics, anesthesiology, and pediatrics at Harvard Medical School and a senior associate in critical care medicine at Children’s Hospital Boston. The opinions expressed are the views of the authors and do not necessarily reflect the policy of the National Institutes of Health, the Public Health Service, or the U.S. Department of Health and Human Services.