Another question here on comas made me read up a bit on them. Apparently, there’s a scale where one can measure how deep a coma is called the Glasgow coma scale. Quoting from Wikipedia:
The Eye and Verbal response parameters seem obvious. But the motor responses 2, 3, 4 and 5 aren’t clear to me. Why is it that one is considered in a deeper coma if they’ll extend when they feel pain, as compared to if they withdraw?
What’s the logic behind the definitions of M2, M3, M4, and M5?
Thanks.
Well, I don’t have any of my reference books right in front of me, but here’s the basic rationale:
1 and 6, as you stated, are straightforward. No movement = bad, obeys commands = good.
#5 might be a somnolent patient who, when pinched on the arm, can slap away the person doing the pinching. The idea is that the patient is able on some level to identify a painful stimulus, the source, and make some effort to stop it.
#4 is less active, a withdrawl from pain. In this case, rather than slapping the pincher away, the patient merely withdraws the pinched limb. Withdrawl from pain is a more basic response and implies less cognitive function.
#3 and #2 are more basic still. In these two instances the patient is unable to make any purposeful movement at all, but in response to a painful stimulus either flexes one or more limbs, or extends one or more limbs. These responses are controlled by the brain stem and spinal cord and are progressively more primitive.
Anyway. In the ER it gets used all the time and it has implications for prognosis. You’ll note that even a rock has a GCS score of 3. I myself spend most of my time between 6 & 7, which I find adequate to get me through the day.
OK, neuro patients were a lifetime ago, so this will be very basic (and I’m sure others can provide a more detailed response)…
If I were to hold your hand over a fire, and you turned your elbows out and tried to touch your fingertips to the inside of your wrists (and did pretty much the same with your legs), that would be…odd, no? I would expect you to yank your hand away (and shout WTF and try to land a haymaker). I don’t mean to be flip.
in a basic neuro assessment like the GCS, the question is “what level of responsiveness is there?”. You don’t respond to voice, so I’ll try other means. “Noxous stimuli” is one way to get a response.
Experience has shown that different levels of brain injury result in different responses to painful stimuli. Those with the gravest injuries don’t respond at all. Next step up is decerebrate posturing (the extension and rotation of extremities I mentioned above). This posturing isn’t only with the extremity being “stimulated”, but involves all extremities. It is not a “local” response, but rather a whole body response to a local stimulus. Next is decorticate posturing, where the arms are drawn in across the chest, fists clenched. Again, a global response to a local stimulus. Etc up the scale of responses.
There is no “logic” behind it, not in the sense of “Hmmm, with this level of injury involving these sensory and motor pathways, it would logically follow that a person would respond thusly based on known anatomic and physilogic properties”. The significance was derived from observational experience. Decerebrate posturing is indicative of brainstem injury - very bad. Decorticate posturing is indicatave of injury to the corticospinal tract - very bad, but less so than brain stem injury.
Jake