i) Glasgow Coma Score

The severity of traumatic brain injury is measured using a series of different scales or assessment tools.

At the point of injury, one of the immediate effects is that a person exhibits a depressed or altered state of consciousness. This may include a period of coma (a loss of consciousness). The depth of unconsciousness can be measured on the Glasgow Coma Scale. The severity of the brain injury is related to the degree of unconsciousness.

The severity of brain injury can be classified according to the Glasgow Coma Score. This scale was devised in the mid-1970s in the hope to try and classify with more accuracy the severity of brain injury as it was thought that severity of brain injury may have some influence with regard to outcome and the ultimate prognosis of the person with a TBI.

There are three classifications of severity of traumatic brain injury when using the Glasgow Coma Scale.

• mild traumatic brain injury is defined when the GCS is between 13 to 15; 15 is a normal score.
• a moderate traumatic brain injury is when the GCS is between 9 to 13 and
• a severe traumatic brain injury is when the GCS is below 8. Generally people have a score between 3-8 for a severe traumatic brain injury, scores less than 3 are not compatible with life.

 

ii) Posttraumatic amnesia

Another method of classifying the severity of traumatic brain injury is determined by the period of posttraumatic amnesia (PTA).

As people emerge from a coma, they go through a period of posttraumatic amnesia (PTA), during which the person is not orientated to time, place, person, and is unable to learn. They may display disinhibition, irritable or agitated behaviour. This is in contrast to the many misleading media portraits, in which a person emerges from a comatose state, as if waking from sleep, fully lucid and oriented. The period of coma and/or PTA, can range from a matter of minutes, through to days, weeks or even months. The duration of PTA is measured until continuous memory is restored. Duration of PTA, as a measure of initial injury severity, is the best predictor of long term outcome after a TBI.

PTA is the period of time it takes from the moment of injury until the person regains not only consciousness but the capacity to remember and learn new material. This can be assessed using a series of rating scales.

In Australia  the Westmead Posttraumatic Amnesia Scale is commonly used to prospectively assess length of PTA. PTA can also be retrospectively estimated by taking a history.  Retrospective assessment of PTA can be unreliable.  The use of a scale such as the Westmead Posttraumatic Amnesia Scale provides a prospective assessment and  a reliable estimate of PTA.

The Westmead scale has been devised in clinical populations, issues such as medication and concurrent medical illness is not thought  as significant influencing factors for the length of PTA.  In cases of PTA less than one week, narcotic administration may alter the duration of PTA.

We have three ratings of severity of injury using the Westmead Posttraumatic Amnesia Scale:

Mild is a posttraumatic amnesia of less than one hour. Moderate is a posttraumatic amnesia of one hour to less than 24 hours.  Severe is a posttraumatic amnesia of 1 to greater than 1day.

Severe can be further classified as:

Severe 1 – 7 days posttraumatic amnesia.
Very severe 8 – 28 days posttraumatic amnesia.
Extremely severe greater than 28 days posttraumatic amnesia.