Coma
Medical Author: Benjamin C. Wedro, MD, FAAEM
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
What is a "coma"?
Coma is a state of unconsciousness whereby a patient cannot react with the
surrounding environment. The patient cannot be wakened with outside physical or
auditory stimulation. The inability to waken differentiates coma from sleep.
Patients can have different levels of unconsciousness and unresponsiveness
depending upon how much or how little of the brain is functioning.
What is the Glasgow Coma Scale?
The Glasgow Coma Scale was developed to provide health-caregivers a
simple way of measuring the depth of coma based upon observations of eye
opening, speech, and movement. Patients in the deepest level of coma:
- do not
respond with any body movement to pain,
- do not have any speech, and
- do not open
their eyes.
Those in lighter comas may offer some response, to the point they may
even seem wake, yet meet the criteria of coma because they do not respond to
their environment.
| Glasgow Coma Scale
|
| Eye Opening |
|
| Spontaneous |
4 |
| To loud voice |
3 |
| To pain |
2 |
| None |
1 |
| |
| Verbal Response |
|
| Oriented |
5 |
| Confused, Disoriented |
4 |
| Inappropriate words |
3 |
| Incomprehensible words |
2 |
| None |
1 |
| |
| Motor Response |
|
| Obeys commands |
6 |
| Localizes pain |
5 |
| Withdraws from pain |
4 |
| Abnormal flexion posturing |
3 |
| Extensor posturing |
2 |
| None |
1 |
The scale is used as part of the initial evaluation of a patient, but does not
assist in making the diagnosis as to the cause of coma. Since it "scores" the
level of coma, the GCS can be used as a standard method for any health-caregiver to assess change in patient status.
There are many causes of coma, but to understand unconsciousness, we need to
know why a person is awake. The brain is a large organ with many parts. There
are two main portions when separated down the middle (right and left cerebral
hemispheres) containing the frontal, parietal, temporal and occipital lobes,
where movement, sensation, speech and thought are housed. The cerebellum sits
under the cerebral hemispheres and is where balance and coordination are
located. The brain stem is where automatic responses to the body including heart
rate, blood pressure, and breathing are controlled. The reticular activating
system (RAS) is located within the brain stem and is the important "on/off"
switch of the brain.
- To be awake, the reticular activating system (RAS) must be functioning, as
well as at least one cerebral hemisphere.
- If a person loses consciousness, either the RAS has stopped working, or both
cerebral hemispheres have shut down.
The reticular activating system stops working in two situations:
- Brain stem stroke:
cells in that area of the brain stem have lost oxygen
and glucose supplied by blood flow,
then function stops. This is either ischemic
(where blood supply is lost) or hemorrhagic (where bleeding occurs and the
structures fail).
- A pre-death
event: increased swelling in the brain pushes down on the brain stem and
causes it to fail. To have both cerebral hemispheres fail requires the
blood supply to the brain be compromised, or some sort of toxic insult has
occurred to all brain tissue.
Next: What are the causes of a coma? »
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