Aug 15 2008

Persistent Vegetative State – From Schiavo to Egnor

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Last week I wrote an entry about the Terri Schiavo case, discussing a new published study criticizing the news reporting of this controversial case. The case involved the right to life of a woman in a persistent vegetative state (PVS) and the relative rights of her husband vs her parents to decide her care. Michael Egnor, a neurosurgeon who writes for the Evolution News & Views blog, and with whom I have had a long blog debate, mostly about dualism and the nature of consciousness, has responded to my post on Schiavo. Not surprisingly he has taken a different view of the case. He writes:

In my view, the political efforts to save Ms. Schiavo’s life were well-intentioned and completely justified. I believe that many of the medical opinions offered publicly by physicians who favored withdrawal of Ms. Schiavo’s hydration and nourishment were rank pseudoscience. What was done to Ms. Schiavo was an atrocity.

He also offers to have a blog discussion about the topic with me, writing:

A detailed and thoughtful public exchange of views about the Terri Schiavo case by two experts in neurological medicine—an academic neurologist and an academic neurosurgeon who have quite different opinions on this matter—would be very informative. The discussion could take the form of detailed exchanges between Dr. Novella and me on specific aspects of the case, such as the autopsy report, the neurological exams, the nature and reliability of the diagnosis of persistent vegetative state, and the ethical and political issues involved. This discussion extends to many of the issues involving the materialist inference in neuroscience that Dr. Novella and I have debated over the past year.

So here is my first installment. I will focus on the nature of persistent vegetative state and respond to some of the comments of Dr. Egnor.

Persistent Vegetative State

Dr. Egnor defines PVS thusly:

“Persistent vegetative state,” defined succinctly but accurately, is the denial of subjective experience in a brain-damaged human being. PVS is the medical assertion that a human being is an object, but not a subject.

I disagree. The first assertion, that PVS is defined as the lack of subjective experience, is misleading, and the second assertion, that the diagnosis of PVS is a statement that a person is an object, is wrong. The latter comment is more straightforward to deal with. A person diagnosed as being in a PVS is still, legally, medically, ethically, a person. They are most certainly not an object and are not treated as such. All of the medical ethics of a living person are still in play.

By contrast, the diagnosis of brain death does render a person an object – specifically a corpse. Once legally declared brain dead a person is dead. They can now legally and ethically be treated as a corpse. You can harvest their organs, perform an autopsy, and bury them.

In what sense does Dr. Egnor claim a person in a PVS is an object? Demonstrably – in no practical sense. He needs to clarify this statement. He may be referring to the fact that life-sustaining care can be withdrawn. However, living people have the right to refuse medical treatment, even if that treatment is necessary to maintain life. People who, for whatever reason, are unable to make their wishes known or who are not mentally competent to make decisions for themselves will have someone to make health care decisions for them. This defaults to the next of kin, or anyone can appoint a health care power of attorney if in the future they are in a position where they cannot make decisions for themselves, or the court may appoint a health care proxy. Such a person has the right to refuse treatment on behalf of the patient – including refusing life-saving interventions.

The point is that conscious or unconscious, competent or not, the rights of a person in a PVS are the same as anyone. The only difference is that they cannot communicate their wishes (regardless of why they cannot). It is even possible, through a living will, for someone to make a decision for themselves – in advance.

Dr. Egnor’s other assertion – that PVS is defined as the lack of subjective experience, is misleading because it is incomplete. That is the inference that is made, but it is not operationally how the diagnosis is made. Here is one definition, published in the New England Journal of Medicine:

The vegetative state is a clinical condition of complete unawareness of the self and the environment, accompanied by sleep-wake cycles, with either complete or partial preservation of hypothalamic and brain-stem autonomic functions. In addition, patients in a vegetative state show no evidence of sustained, reproducible, purposeful, or voluntary behavioral responses to visual, auditory, tactile, or noxious stimuli; show no evidence of language comprehension or expression; have bowel and bladder incontinence; and have variably preserved cranial-nerve and spinal reflexes.

The diagnosis of PVS is made on the basis of the absence of evidence for conscious awareness, while retaining some brain reflexes. It is generally understood that we cannot know what is actually going on in the “mind” of the patient. We can only infer from the exam and from other lines of evidence, such as the exam findings outlined in the quote above.

But also a complete neurological assessment will also involve imaging of the anatomy of the brain. If the cortex is clearly severely and diffusely damaged by MRI scanning, that supports the clinical diagnosis of PVS. In addition we can use EEG to look at the degree of electrical activity of the cortex. If a patient displays no signs of conscious awareness, has diffuse damage on MRI, and has reduced electrical activity on EEG, those are three independent lines of evidence leading to the same conclusion – severe brain damage.

It is important to distinguish the methods of assessing a patient and making a diagnosis from the inferences that are drawn from that evidence. In conflating the two Dr. Egnor makes it seem as if we are pretending to read the minds of comatose patients.

There are two aspects of the PVS diagnosis that are important to treatment decisions. The first is an estimate of the level of consciousness that a person currently has. This is an important piece of information in assessing their current quality of life. The second issue is their prognosis – what is the probability that they will improve in the future. These are the two factors that people always want to know in making decisions for their loved ones – what are they experiencing now, and what is their chance for improvement?

I always emphasize to families in such situations that we can never be completely certain. We can only make evidence-based judgments. I am usually also careful to say, for example, “there is no evidence from my exam that there is any conscious awareness,” rather than a more definitive statement that there is no awareness. I will then give the family a sense of my confidence. This depends on many variable – the age of the patient, the time since the injury, the severity of the exam, and the extent of damage seen on imaging and EEG.

My job is not to make the decision for the family, but to give them the best medical facts we have available so that they can make an informed decision. It is up to them to weigh issues of quality of life, their religious or metaphysical beliefs, and their assessment of what their loved-one would have wanted. I do not get directly involved with such considerations – nor should I. The role of science is to inform such decisions, not make them.

Prognosis is an easier question to answer than assessing current quality of life. In patients who have been in a PVS for more than 6 months recovery is extremely rare. There are cases of recovery, which garner great media attention, but they are the rare exception.

Current Difficulties

From Dr. Egnor’s initial post on this topic I imagine he is going to review all of the difficulties in diagnosing a patient with PVS. I am going, to an extent, preempt him by acknowledging up front that there are many difficulties with the diagnosis of PVS and the inferences that we draw from it. The neurological exam is a very poor tool for examining cortical function in a patient that cannot follow commands or communicate. I tell this to students all the time – all we can say is that there is an absence of evidence for cortical activity, but we must acknowledge the limitations of the exam. That is why we must combine that information with MRI, EEG, and other tools.

Of note, as new tools for looking at brain activity are coming into use, such as function MRI scanning, we are learning more about the possible conscious state of patients in PVS and related conditions. Not surprisingly, as more accurate tools come into use we are discovering the inaccuracies of our prior tools. This is a common and expected experience. I certainly hope that as our technology advances we will be able to make more precise and reliable diagnoses of patients in various types of coma – so as to better inform those who must make care decisions.

It is also true that our statements are largely statistical, and we can be wrong in an individual case. Although sometimes the statistics can be overwhelming (the chance of waking up from a PVS that has persisted for more than 6 months is truly vanishingly small), they are still just statistical – not predictions of the future.

But, I would argue that this is no different than all of medicine. Medicine is an applied science. It is the practice of making the best inferences we can from the data we are able to obtain. It involves making statistical statements about probable outcomes in order to make treatment decisions. I am sure that Dr. Egnor does not give his patients absolute certainties about the outcomes of their surgery. A surgeon can only advise a patient as to the likely outcome of operating – or not operating, on their condition.

For example, if someone has a ateriovenous malformation (AVM) we can tell them what the probability is that the AVM will cause a major bleed in the future, and compare this to the risk of surgery and the probable benefit of surgery. These are all statistical statements. No one knows what will actually happen to an individual patient with or without surgery.

This is exactly the same situation with PVS. We can tell families, to the best current available medical knowledge, what the likely condition of their loved-one is and what their likely prognosis is.

Conclusion

In a future post I will discuss the Terri Schiavo case specifically, in light of the above discussion.

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