Alterations in Level of Consciousness, Coma

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Alterations in Level of Consciousness, Coma S30 ()

Alterations in Consciousness, Coma

Last updated: September 5, 2017

Definitions 1

Pathophysiology 3

Anatomy of Arousal 3

Substrate of Coma 6

Anatomy of Awareness 6

Anatomy of Attention 7

Etiology 7

Initial Examination and Stabilization 7

Short History 9

Glasgow Coma Scale 9

Glasgow-Liege scale 14

Sedation Scale 14

Children Coma Scales 15

FOUR score 16

Further Medical Examination 16

Further Neurological Examination 18

Clinical Findings with Different Levels of CNS Dysfunction 29

Instrumental Neurologic Examination 30

Management 33

Prognosis 36

Etiologic Categories 36

Coma-like states 38


Consciousness - set of neural processes that allow individual to perceive, comprehend, and act on internal and external environments; consciousness has two parts:

  1. Arousal - describes degree to which individual is able to interact with environments; waking and sleeping are two different states of arousal; generally, awake = aroused = alert.

  2. Awareness - depth and content of aroused state (i.e. individual is not only alert but is cognizant of self and surroundings, so some authors use term cognition).

    • awareness depends on arousal (one who cannot be aroused lacks awareness).

    • awareness is not modality specific (i.e. equal for all types of stimuli).

    • attention - ability to respond to particular types of stimuli (modality specific); attention depends on awareness.

In general use, consciousness = awareness

To diagnose awareness, one must demonstrate response to various stimuli - several modalities (typically, verbal, visual, and somatosensory) presented from both sides of patient.

N.B. inattention to stimuli chosen could be misinterpreted for unawareness (e.g. failure to respond to verbal commands on part of deaf patient).

Gradations of consciousness:

N.B. many terms lack consistent definitions; physician should clearly describe what patient does spontaneously and in response to various stimuli.

Occasionally, true level of consciousness is difficult to determine (e.g. in catatonia, severe depression, curarization, akinesia plus aphasia).

Coma - profound unconsciousness from which patient cannot be aroused ("nesužadinama, nekontaktinė būsena su užmerktomis akimis").

  • patient lies still (when not stimulated).

  • patient does not make attempt to avoid noxious stimuli!

If patient responds to noxious stimuli by any defensive maneuver, patient is not truly comatose (noxious stimulus powerfully evokes arousal response).

  • eyes are closed! (except vertical eye movements that may accompany suppression-burst EEG pattern).

  • cerebral oxygen uptake is abnormally reduced (vs. normal in sleep or even increased during REM stage).

Stupor - impaired consciousness when only continual intense stimulation arouses patient.

Obtundation, lethargy, sopor - unnaturally deep sleep; patient appears to be asleep much of time when not being stimulated (i.e. patient can be aroused but immediately relapses into sleep).

N.B. it is not EEG sleep!

Drowsiness - simulates light sleep - patient can be easily aroused (by touch or noise) and can maintain alertness for some time.

After period of coma, CNS may re-establish consciousness - patient enters vegetative state (unresponsive wakefulness) – state of arousal without awareness; see p. S32 >>

  • do not respond to any stimuli (auditory, painful, hunger, or other).

    If some response is preserved - minimally responsive state (minimally conscious state):

    "MRS-minus" - patients show low-level behavioral responses, such as reacting to pain or following with the eyes.

    "MRS-plus" - patients are additionally able to follow commands, to verbalize intelligibly, and/or to communicate nonfunctionally.

  • eyes open and close, appear to track objects about room.

N.B. spontaneous eye opening is sign of arousal, not awareness!

  • may chew and swallow food placed in mouth.

  • patient manifests sleep-wake cycling.

  • histopathology - loss of cortex with preservation of ARAS.

Delirium - state of awareness without attentiveness, i.e. disturbance of consciousness (ARAS dysfunction) + clouding of consciousness* (cortex dysfunction) → inability to maintain attention → global change in cognition. see p. S15 >>

* reduced mental clarity, altered mental content (confusion)

  • patient may be hyperactive (rather than lethargic) with heightened alertness.

  • may alternate with obtundation, stupor, coma.


Anatomy of Arousal

Reticular Activating System (RAS)

- complex polysynaptic pathway in rostral* reticular formation of brainstem. see p. A57 (2-5) >>

* paramedian tegmental gray matter of midbrain & diencephalon (pontine RF is not necessary for arousal!)

  • collaterals funnel into RAS from all long ascending sensory tracts and also from trigeminal, auditory, visual, and olfactory systems.

RAS receives collaterals from and is stimulated by every major somatic and sensory pathway directly or indirectly.

  • degree of convergence abolishes modality specificity - reticular neurons are activated with equal facility by different sensory stimuli (nonspecific system).

    • RAS projects to thalamic nuclei (intralaminar and related) → projected diffusely & nonspecifically to whole neocortex:

    activation of these areas is shown by PET during shift from relaxed awake state to attention-demanding task.

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