Whether or not the accident victim was in a coma, and the length of that coma is one of the parameters that best reflects the severity of the brain injury. Unfortunately, there are multiple definitions of a coma. But, everyone can agree that a coma is a period of unresponsiveness or unconsciousness. But, not everyone can agree on the degree of responsiveness that indicates the end of a coma.
In a medical setting, spontaneous eye opening is sometimes used as a marker for the end of a coma. The problem is that using this definition for everyone with very severe injuries is that everyone with a TBI will eventually begin to spontaneously open their eyes. However, a very small minority will not regain any further ability to interact with the environment. They will be in a semi-vegetative state. Because of this, in a rehabilitation setting, coma is most commonly considered to be over when the brain injured accident victim follows simple commands. This proves to the observer that some meaningful interaction has taken place. Some experts disagree with using this as the end point of coma. However, the duration of the coma is defined this way, and has been shown to correlate to long-term outcome.
Research has found that six hours or more of coma indicates a severe TBI. However, the International Classification of Diseases classifies severity of TBI as follows:
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