Disorders of consciousness
Disorders of consciousness | |
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Specialty | Neurology, psychiatry |
Disorders of consciousness are
Classification
Patients in such a dramatically altered state of consciousness present unique problems for diagnosis, prognosis and treatment. Assessment of cognitive functions remaining after a traumatic brain injury is difficult. Voluntary movements may be very small, inconsistent and easily exhausted. Quantification of brain activity differentiates patients who sometimes only differ by a brief and small movement of a finger.[citation needed]
Consciousness is a complex and multifaceted concept, divided into two main components: Arousal and Awareness. Arousal is associated with functional brainstem neuron populations projecting to both thalamic and cortical neurons.[6] Therefore, the assessment of reflexes (Using the Glasgow Coma Scale) is important to investigate the functional integrity of the brainstem. Awareness is thought to be related with functional integrity of the cerebral cortex and its subcortical connections. The most important point regarding the classification of disorders of consciousness is, that consciousness cannot be measured objectively by any machine, although many scoring systems have been developed for the quantification of consciousness and neuroimaging techniques are important tools for clinical research, extending our understanding of underlying mechanisms involved.[7][8] Disorders in consciousness represent immense social and ethical issues because the diagnosis is methodologically complex and needs careful interpretation. Also the ethical framework must be further developed to guide research in these patients.[citation needed]
Locked-in syndrome
In
Minimally conscious state
In a minimally conscious state, the patient has intermittent periods of awareness and wakefulness. The criteria for minimally conscious state, that patients are not in a vegetative state but are not able to communicate consistently. This means, that patients have to show limited but reproducible signs of awareness of themself or their environment. This could be following of simple commands, intelligible speech or purposeful behavior (including movements or affective behavior in relation to external stimuli, but not reflexive activity).[11] Further improvement towards full conscious recovery is more likely in this state than in the vegetative state, but still some patients remain in the MCS constantly.[12]
Persistent vegetative state
In a
Chronic coma
Although a coma patient may appear to be awake, they are unable to consciously feel, speak, hear, or move. For a patient to maintain consciousness, two important neurological components must function impeccably. The first is the cerebral cortex which is the gray matter covering the outer layer of the brain. The other is a structure located in the brainstem, called
Brain death
Brain death is the irreversible end of all brain activity, and function (including involuntary activity necessary to sustain life). The main cause is total necrosis of the cerebral neurons following loss of brain oxygenation. After brain death the patient lacks any sense of awareness; sleep-wake cycles or behavior, and typically look as if they are dead or are in a deep sleep-state or coma. Although visually similar to a comatose state such as persistent vegetative state, the two should not be confused. Criteria for brain death differ from country to country. However, the clinical assessments are the same and require the loss of all brainstem reflexes and the demonstration of continuing apnea in a persistently comatose patient (< 4 weeks).[18] Functional imaging using PET or CT scans, typically show a hollow skull phenomenon. This confirms the absence of neuronal function in the whole brain. Patients classified as brain dead are legally dead and can qualify as organ donors, in which their organs are surgically removed and prepared for a particular recipient.[citation needed]
Brain death is one of the deciding factors when pronouncing a trauma patient as dead. Determining function and presence of necrosis after trauma to the whole brain or brain-stem may be used to determine brain death, and is used in many states in the US.[citation needed]
Methodological problems
Metabolic studies are useful, but they are not able to identify neural activity within a specific region to specific cognitive processes. Functionality can only be identified at the most general level: Metabolism in cortical and subcortical regions that may contribute to cognitive processes.[citation needed]
At present, there is no established relation between cerebral metabolic rates of glucose or oxygen as measured by
Ethical issues
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Disorders of consciousness present a variety of ethical concerns. Most obvious is the lack of consent in any treatment decisions. Patients in PVS or MCS are not able to decide for the possibility of withdrawal of life-support. It is also a general question whether they should receive life-sustaining therapy and, if so, for what duration. The problems regarding a patient's consent also account for neuroimaging studies. Without patient's consent, such studies are perceived as unethical.[24] Additionally, only few patients have created advance directives before losing decision-making capacity.[citation needed] Typically, approval must be obtained from family or legal representatives depending on governmental and hospital guidelines but, even with the consent of representatives, researchers have been refused grants, ethics committee approval and publication.[citation needed]
Social issues arise from the enormous costs associated with people who have disorders of consciousness, especially chronic comatose and vegetative patients, when recovery is highly unlikely and treatment in the ICU is considered futile by clinicians.[citation needed] In addition to the aforementioned problems, the question rises why medical resources were being used not for the broader public good but for patients who seemed to have only little to gain from them. Nevertheless, the irreversibility of these conditions remains an open question. Some studies demonstrated that some patients with disorders of consciousness may be aware despite clinical unresponsiveness.[citation needed] These findings could have a major impact on ethical and social issues.[25]
See also
References
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- ^ Steriade M, Jones BG, McCormick D. Thalamus. New York Elesevier, 1997.
- ^ Laureys S, Majerus S, Moonen G. Assessing consciousness in critically ill patients. In: Vincent JL, ed. 2002 Yearbook of Intensive Care and Emergency Medicine. Heidelberg: Springer-Verlag, 2002: 715-27
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- ^ American Congress of Rehabilitation Medicine. Recommendations for use of uniform nomenclature pertinent to patients with severe alternations of consciousness. Arch Pyhs Med Rehabil 1995; 76;: 205-9
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: CS1 maint: multiple names: authors list (link - ^ a b Laureys, Steven, Adrian M. Owen, and Nicholas D. Schiff. "Brain function in coma, vegetative state, and related disorders." The Lancet Neurology 3.9 (2004): 537-546.
- ^ Giacino JT. Disorders of consciousness: differential diagnosis and neuropathologic features. Semin Neurol 1997; 17:105-11
- ^ Laureys S, Faymonville ME, Goldman S, et al. Impaired cerebral connectivity in vegetative state. In: Gjedde A, Hansen SB, Knudsen GM, Paulson OB, eds. Physiological imaging of the brain with PET. San Diego: Academic Press, 2000: 329-34.
- ^ Tommasino C, Grana C, Lucignani G, Torri G, Fazio F. Regional cerebral metabolism of glucose in comatose and vegetative patients. J Neurosurg Anesthesiol 1995; 7: 109-16
- ^ Menon DK, Owen AM, Williams EJ, et al. Cortical processing in persistent vegetative state. Lancet 1998; 352: 200.
- ^ Bersneider M, Havda DA, Lee SM, et al. Dissociation of cerebral glucose metabolism and level of consciousness during the period of metabolic depression following human traumatic brain injury. J Neurotrauma 200; 17: 389-401
- ^ Plum F, Posner JB. The diagnosis of stupor and coma (3rd edn). Philadelphia: FA Davis, 1983.
- ^ Medical Consultants on the Diagnosis of Death. Guidelines for the determination of death: report of the medical consultants on the diagnosis of death to the President's commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research. JAMA 1981; 246: 2184-86
- ^ Maquet P, Degueldre C, Delfiore G, et al. Functional neuroanatomy of human slow wave sleep. J Neurosci 1997; 17 2807-12
- ^ Buchsbaum MS, Gillin JC, Wu J, et al. Regional cerebral glucose metabolic rate in human sleep assessed by positron emission tomography. Life Sci 1989; 45: 1349-56
- ^ Wu HM, Huang SC, Hattori N, et al. Selective metabolic reduction in gray matter acutely following human traumatic brain injury. J Neurotrauma 2004; 21: 149-61
- ^ Hovda DA, Becker DP, Katayama Y. Secondary injury and acidosis. J Neurotrauma 1992; 9 (suppl 1): S47-60
- ^ Meltzer CC, Zubieta JK, Links JM, et al. MR-based correction of brain PET measurements for heterogeneous gray matter radioactivity distribution. J Cereb Blood Flow Metlab 1996; 16: 650-58
- ^ Fins JJ. Constructing an ethical stereotaxy for severe brain injury: balancing risks, benefits and access. Nat Rev Neurosci 2003; 4: 323-27.
- ^ Jox RJ, Bernat JL, Laureys S, Racine E. Disorders of consciousness: responding to request for novel diagnostic and therapeutic interventions. Lancet Neurol. 2012; 11(8): 732-38