Coma And Impaired Conscious Level

Consciousness is regarded as a state of awareness of self and surroundings. Impaired consciousness is due to disturbed arousal or content of mental function.

Many pathological processes may impair conscious level and numerous terms have been employed to describe the various clinical states which result, including obtundation, stupor, semicoma and deep-coma. These terms result in ambiguity and inconsistency when used by different observers. Recording conscious level with the Glasgow coma scale (page 5) avoids these difficulties and clearly describes the level of arousal. With this scale:

COMA = NO SPEECH, NO EYE OPENING, NO MOTOR RESPONSE

In this section we describe conditions which may present with, or lead to, coma. Patients experiencing 'transient disturbance of conscious level' require a different approach.

Pathophysiology of coma

A 'conscious' state depends on intact cerebral hemispheres, interacting with the ascending reticular activating system in the brain stem, midbrain, hypothalamus and thalamus. Lesions diffusely affecting the cerebral hemispheres, or directly affecting the reticular activating system cause impairment of conscious level:

Diffuse hemisphere damage e.g. - trauma

- ischaemia

- hypoglycaemia

- hepatic or renal failure

[Note: focal damage to part of the cortex does not affect conscious level]

[Note: focal damage to part of the cortex does not affect conscious level]

Bilateral thalamic involvement, e.g. astrocytoma

Supratentorial mass causing transtentorial herniation - and midbrain compression

Brain stem compression - directly from infratentorial mass lesion

Brain stem involvement

- ischaemia

- haemorrhage

- tumour

- drugs (sedatives, hypnotics)

Bilateral thalamic involvement, e.g. astrocytoma

Supratentorial mass causing transtentorial herniation - and midbrain compression

Brain stem compression - directly from infratentorial mass lesion

- or indirectly from tonsillar herniation

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