Dr Gilberto Leung and Dr Gary Lau
Our level of consciousness is governed by our cerebral cortex as well as the subcortical ascending reticular formation. Patients with normal consciousness have a high level of arousal and awareness, whilst the level of arousal and awareness is low in patients who are comatosed.
The level of arousal of a patient is mainly controlled by the subcortical ascending reticular formation and can be assessed by determining their eye opening response to a variety of stimuli.
In contrast, awareness is mainly controlled by the cerebral cortex, and can be assessed by one’s verbal and motor response, again to a variety of stimuli.
One’s conscious level, is therefore often affected by pathologies that affect the subcortical ascending reticular formation or cerebral cortex. The reticular formation may be affected by brainstem pathologies such as a stroke or demyelinating diseases. Whilst the cortex maybe affected by a large cortical lesion (e.g. stroke, tumour or infection), or pathologies affecting the cortex as a whole such as infections (meningitis or severe sepsis causing septic encephalopathy), severe metabolic disturbances (hepatic and uremic encephalopathy) or even due to side effects of drugs (barbiturates, benzodiazepines etc.).
The Glasgow Coma Scale (GCS) is a standardized method of assessing one’s conscious state. It can be conveniently performed at the bedside and incorporates the assessment of one’s eye opening response (arousal), as well as verbal and motor response (awareness) into a simple scale. The scale ranges from 3 to 15. A score of 3 means that the patient is completely comatosed, whilst 15 suggests that the subject is fully conscious and alert. The breakdown of the individual components is as follow:
Eye opening (total score of 4):
4: Spontaneous eye opening
3: To speech
2: To pain
1: No eye opening
Verbal response (total score of 5):
T: Not assessible (e.g. in an intubated patient)
5: Oriented conversation
4: Confused speech
3: Inappropriate words
2: Incomprehensible sounds
1: No verbal response
Motor response (total score of 6):
6: Obeys simple commands
5: Localises pain
4: Withdrawal response to pain
3: Stereotyped flexion to pain
2: Stereotyped extension to pain
1: No motor response
An example of how the GCS is performed is being demonstrated in the video shown here. In order to elicit pain, a number of areas could be stimulated which include the sternum, supra-orbital ridges and nailbeds of the fingers or toes.
There are a number of entities of patients with impaired consciousness which may be of interest. The first one being patients with “unresponsive wakefulness syndrome”. Many people refer these patients as in a “vegetative state”. However, use of such a term should be discouraged as this term is associated with a negative meaning. In patients with unresponsive wakefulness syndrome, they are fully arousable (i.e. they are awake and can open their eyes). However, they have impaired awareness with marked impairment in their motor response.
Another entity of interest is patients with “locked-in syndrome”. These are often caused by strokes at the ventro-pontine region, thus affecting the cortico-spinal and cortico-bulbar tracts. These patients are therefore fully aroused and aware of their surroundings. However, as their cortico-spinal tract is affected, they are unable to move their limbs. These patients therefore communicate by eye-blinking.