Can people who are unconscious or in the 'vegetative state' perceive pain.

• Author: McQuillen, Michael P.

"The problem of pain," as C.S. Lewis described it, is one posed by the evolution or appearance of man on planet earth. (1) Man is a being possessed of mind, of consciousness, and of soul--qualities or entities beyond the limits of this article, but upon which the language and recognition of pain depend most critically. As Petrie put it,

There is nothing is human experience more central than our capacity to feel, and no aspect of this so crucial as our capacity to suffer, perhaps more particularly to suffer from extremes of physical pain. (2)

Definition of Terms

People

It is important to recognize from the outset that, although an understanding of much of the basic anatomy, physiology, and pharmacology of pain derives from studies in animals other than man, our concern will--for the most part--be limited to the phenomenon in man.

Unconsciousness

The physical basis and definitional character of consciousness have been described elsewhere. (3) However, it is important to emphasize the will-o-the-wisp nature of the concept and to recall the judgment of the preeminent neurologist of the last century, Hughlings Jackson, that "[t]here is no such entity as consciousness; we are from moment to moment differently conscious." (4) Thus it is that the absence of consciousness--the unconscious state--is defined in essentially negative terms: "insensible; incapable of responding to sensory stimuli and of having subjective experiences." (5) The question is, how do you know that a person is unconscious--that is, "incapable of responding to sensory stimuli"--if you cannot gain access to his subjective experience? As a physician, one of whose major areas of professional interest has been neuromuscular disease, the author agrees with the distinguished neurophysiologist Sherrington, who opined that muscle is the cradle of recognizable mind. (6) If the muscles of speech or those involved with writing do not communicate in a fashion that can be understood, is it legitimate to conclude that there is no experience for them to communicate? As the grandfather of Claire McQuillen, only recently a year of age, the author knows that cannot be so!

"Vegetative State"

In 1972 Jennett and Plum put forth a point of view with regard to a group of patients who, owing to improved acute and intensive care, had survived severe traumatic or ischemic brain damage. (7) Such patients survive in a sleeplike, insensible state, neither unconscious nor in coma, and never show evidence of a working mind. (8) They are wakeful without being aware: their eyes open spontaneously or in response to verbal stimuli, but they do not obey commands, express comprehensible words, or sustain visual fixation and pursuit. (9) They do manifest sleep/wake cycles and maintain cardiorespiratory function. (10) For the most part they are described as exhibiting only patterned responses to noxious stimuli, not complex, intelligible communication. (11) Jennett and Plum state:

[T]he indefinite survival of patients in this state presents a problem with humanitarian and socioeconomic implications which society as a whole will have to consider. If it were possible to predict soon after the brain damage had been sustained that, in the event of survival, the outcome would be a vegetative mindless state, then the wisdom of continuing supportive measures could be discussed. (12)

A variable pathology has been reported with microscopic damage most severe in the neocortex, less so in the hippocampus and thalamus, and least in the brainstem. (13) The neurophysiology of the "vegetative stat" is likewise variable. The electroencephalogram (EEG) shows a range of patterns that have in common no regular change with reference to a changing behavioral state; evoked potentials are normal in the brainstem but are altered at the cortical level in response to somatosensory stimuli. (14) The inference drawn from positron emission tomographic (PET) studies (thus far reported in only seven patients in the "vegetative state" (15)) is that cognitive function is lost because the regional cerebral metabolic rate for glucose is less than half the normal value. (16) This inference must be tempered by evidence that blood flow, not metabolism, is the factor most sensitive to stimuli that elicit a cognitive response. (17) Infants, whose cognition can only be inferred by motor movements not unlike those manifested by the patient in the "vegetative state," (18) have cerebral metabolic rates in excess of healthy adults. (19) This is so in the very regions with regard to which it is inferred, in the "vegetative state," that cognitions is lost because the metabolic rate is low.

In recent years, some researchers have emphasized the essentially clinical nature of the "vegetative state" and have attempted to extend its limits to include the end stage of any chronic, progressive, neurodegenerative disorder at one end of life (20) and to compare it with anencephaly at the other. (21) Such a comparison has obvious pragmatic impact upon any discussion of the ethical consequences of the syndrome (22) but is flawed from the start, since the syndrome is just that: a "set of symptoms which occur together," (23) by no means precise, easily recognized, or even well accepted.

Perception

Easily the most difficult element to grasp in the problem of pain is the concept of perception: how do we know that we know? The language of pain is rich in metaphor and example but very limited in the recognition of what it conveys. Nevertheless, the language is universal and exquisite in its depth--the anguished look of a face in pain; the cry of one in pain; the withdrawal or defensive posture assumed in response to a painful stimulus; the increase in heart rate, blood pressure, and other autonomic concomitants of the reaction to pain. By virtue of the fact that this language is universal and is not limited to man...