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Abnormal consciousness is caused by pathologies that specifically alter the function of a neuronal network responsible for causing awareness and alertness. Understanding of the basic concepts of this arousal system and the pathophysiologic mechanisms underlying its alteration are imperative in the diagnosis, treatment, and long-term management of coma. This chapter will focus on the definition of consciousness, the physiology of arousal, the pathologies underlying coma, the neurologic examination of the comatose patient, management of coma, and assessment of prognosis. Each section is accompanied by a case to illustrate the different clinical scenarios in which coma can present.


CASE 36-1

A 57-year-old woman presented to the emergency department with acute loss of consciousness. She has no relevant past medical history. Her coworkers state she had complained of the worst headache in her life 2 weeks ago that has since resolved. On observation, the patient’s eyes are closed and her respiratory pattern appears irregular. Blood pressure at the bedside is 180/90 mmHg, and heart rate is 54 beats per minute. General examination reveals neck stiffness and bilateral retinal hemorrhages. On neurologic examination, pupillary and corneal responses are present. The patient exhibits no eye opening or motor response to noxious stimuli. Her FOUR score is 6. She is sent for emergent neuroimaging that reveals diffuse subarachnoid hemorrhage (SAH) and obstructive hydrocephalus.

What are the general concepts of consciousness?

Consciousness is a state of full awareness to both self and environment, and is divided into two major categories:1

  • Content

    • Defined as the cognitive and affective responses, which are mediated at a cortical level.

    • Includes language, right and left orientation, reading, writing, behavior, and recognition of faces and colors.

    • Linked closely with the arousal system to maintain the behavioral appearance of wakefulness.

    • Diffuse damage of cortical structures (ie, Alzheimer) can cause a reduced content consciousness.

  • Arousal

    • The ascending arousal system is a diffuse network of afferent mesopontine and diencephalic neurons.

    • Interneurons regulate the relationship between sleep/wake cycles and coordinate phase transition during sleep (ie, non-REM to REM).

    • Ascending neurons target cortical structures, integrating the behavioral and cognitive components of consciousness.

    • Focal or diffuse lesions of the arousal system (ie, infarction) can produce acute alterations in level of consciousness.

What are the definitions of the acutely altered states of consciousness?

  • Delirium:

    • An acute medical condition defined by agitation, clouding of consciousness, and changes in attention that develop over a short period of time.

  • Obtundation:

    • A mild-to-moderate reduction in alertness, accompanied by a lesser interest in the environment, shown clinically by slower responses to stimulation and increased number of sleep hours.

  • Stupor:

    • A moderate-to-severe reduction in consciousness, with or without cognitive impairment, from which a subject can be aroused only with vigorous and continuous stimulation.

  • Coma:

    • A state of unresponsiveness in which the patient lies with eyes ...

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