Pain Care of Severely Neurally-Compromised Patients
Over the past two decades, the issue of pain in obtunded and vegetative patients has attracted considerable attention and has become the focus of ongoing debate in light of both several “high profile cases”1,2 and an increasing capacity for neurotechnology to afford insight and perhaps access into the “brain and mind” of such patients.3 In this latter regard, neurotechnology has enabled an enhanced understanding of the relationship of brain structure to consciousness and this knowledge has instigated pragmatic and ethical concerns about the capacity of severely neurally-compromised patients (SNCPs) to experience pain. Yet there remains some contention as to whether or not pain actually is experienced in patients with severe neural compromise.4 We argue that any approach to this issue must account for (1) the neuroanatomy of pain, (2) the viability of certain neuroanatomical substrates following particular types and extent of brain injury, (3) the potential for re-organization/re-modeling of the injured brain, (4) the capacity of the injured and compromised brain to sustain some form of pain sensation and/or perception, and (5) the phenomenal nature and extent to which such stimulation might affect the person in whom that brain exists.
In this essay, we pose a fundamental question—namely, what extent of cerebral compromise will obviate the sensation and perception of pain as a noxious event? Thus, while cortical function—considered to represent the requisite neuroanatomical substrate(s) for consciousness, if not identity—may be compromised or absent, can we be certain that pain (in some form that retains the qualities of noxiousness) is not processed by sub-cortical structures to an extent that is subjectively experienced? While a loss of reticulo-thalamic activity certainly might be viewed as sufficient to qualify determination that a patient might not be able to process intero- and/or exteroceptive afferent information,5 the clinical picture is less clear given compromise to other central neural substrates. Simply, we do not know “how much” brain is required to evoke and sustain some semblance of self and we cannot be certain whether pain, in some form that is subjectively nocuous, is “felt” by the SNCP—particularly in light of such patients’ inability for efferent reactions and/or expression.
This issue prompts renewed address in light of progressive knowledge of the function of the nervous system; the interaction of brain, mind and pain; potential influence of neurotechnology on limitations of clinical decision-making; and the ethical questions that these factors generate. A growing body of empirical evidence fortifies appreciation that pain sensation and perception can, and likely does, occur in such patients—particularly during the period after initial neural insult—and that this pain warrants clinical consideration especially during the conduct of invasive procedures.6,7
Despite the hundred-year history of anesthesia as a staple measure in almost every invasive medical intervention,8 the provision of anesthesia and/or analgesia to SNCPs during invasive procedures long remained unconsidered based upon the longstanding belief that the compromised brain was insensate to pain. However, this position is becoming increasingly contested, in light of studies that suggest that the neural pathways for pain are not simply cortical but may involve sub-cortical structures that may remain relatively intact and viable after trauma.9 Hence, we opine that there is a need to at least address, if not precautionarily treat, pain in SNCPs.
The neural systems that subserve pain appear to be differentially plastic throughout the lifespan.10-18 However, it is still not fully known how such pain systems react to global neural insult. Thus, despite inactivity of cortical structures following trauma, the reticular-midbrain, hypothalamic-pituitary, and thalamo-limbic pathways may remain viable. Questions remain as to whether each and/or all of these systems, networks and pathways need to be fully functional for the pain experience to occur and whether the experience of “pain” in SNCPs is equally or equivalently noxious to that in the un-compromised patient.
Given the definition of “pain” as “…an unpleasant sensory and emotional experience…”19 then for a subjective phenomenon of noxious sensation to be “experienced” as “pain” it would necessarily involve the substrates and have some combinatory qualities of sensation, cognition and emotion.20 Chugani et al have posited that if specific areas of the cortex that are responsible for the associative aspects of linking sensation to cognition and emotion are not fully functional,21 then the organism cannot “experience” pain qua pain.
However, the “experience” of pain, while involving a number of higher neuroanatomical areas (e.g., the somatosensory and associative cortices), is reliant upon subcortical structures as well. Furthermore, these structures likely do not function site-specifically, but are engaged as, and within, a network. The properties of network contribute to mental process(es) which may vary in each individual and may be “re-directed” and re-modeled as a consequence of pathologic insult. Thus, arguments that attempt to negate the possibility of SNCPs’ pain may be flawed in that they tend to attribute the function of the whole brain to particular parts (i.e., the mereological fallacy).22 Additionally, it is erroneous to assume that pain is uniform across individuals and “knowable” only in terms of its meaning and the capacities used to express it. Both the sensation and experience of “pain” are subjective and individually variant. We cannot “know” what the feeling(s) of pain are like for another person. Rather, we can only comprehend the expression and/or explanation of their experience.23,24,25 The lack of expressive capability does not refute the possibility that other individuals can have pain. Clearly the example of those with “locked-in syndrome” demonstrates this. Given that the existential reality of “being obtunded” or “vegetative’ cannot be subjectively explained, a frame of reference does not exist for these conditions. Therefore, we must rely upon our understanding of the nervous system, as well as our interpretations of neurophysiologic data and behavioral responses to develop a contemporary hermeneutics that allows some appreciation of such experience. Since we do not concretely “know” if SNCPs feel some sort of “pain,” it is important to consider whether the neural substrates that remain functional could mediate noxiousness. If so, then this would support the provision of analgesia to SNCPs—at least during invasive medical procedures.