The brain is very sensitive to the amount of blood getting through to it, so anything which impedes the flow of blood to the brain or lowers oxygen to the brain, can damage it. Poisons in the blood, such as carbon monoxide from car fumes, can poison the brain. Finally there are treatments people can receive in good faith, which can damage the brain, a surgeon operating on the brain to remove a tumor can inadvertently damage it and radiation therapy, which is often used to treat malignant brain tumors, can damage the it especially in young people.
There are two broad guidelines to assess the severity of a brain injury. The first is how unconscious the patient is at their very worst, and this is measured with something called the Glasgow Coma Score, this is usually measured out of 15, 15 is fully conscious and three is as deeply unconscious as you can be and still be alive. The Glasgow Coma Score has three levels in it, one is to do with response to eye movement and eye opening, another is to do with response to speech, and the third is to do with response to movement. These three levels can all be given a number, and that gives you the total figure. Broadly speaking, any head injury in which the Glasgow Coma Score goes to eight or below is classified as a very severe brain injury.
The second things that’s used to assess the severity if a brain injury is what’s called the post traumatic amnesia (PTA), this is the period of time from the accident to when continuous memory returns. The PTA doesn’t shrink, so if a month after a head injury a person has a PTA of an hour, it’s still going to be an hour a year later. The PTA has a very close connection to time taken to get back to work and it’s also one of the factors in the risk of getting late traumatic epilepsy.