Defining Severity of Injury

ABI severity is usually classified according to the level of altered consciousness experienced by the patient following injury. Consciousness levels following ABI can range from transient disorientation to deep coma. Patients are classified as having a mild, moderate or severe ABI according to their level of consciousness at the time of initial assessment. Various measures of altered consciousness are used in practice to determine injury severity. Common measures include the Glasgow Coma Scale (GCS), the duration of loss of consciousness (LOC), and the duration of post-traumatic amnesia (PTA).

Table: The Glasgow Coma Scale

Response/Item

Points

Eye Opening

 

Spontaneous

4

To speech

3

To pain

2

None

1

Motor Response

 

Obeys commands

6

Localizes pain

5

Withdrawal (from painful stimulus)

4

Abnormal flexion

3

Extension

2

None

1

Verbal Response

 

Oriented

5

Confused

4

Inappropriate

3

Incomprehensible

2

None

1

The Glasgow Coma Scale

The GCS is one of the most widely used measures of altered consciousness. Developed by Teasdale and Jennett (1974, 1976) it is comprised of three subsections: eye opening, best motor response, and verbal response (Table 1.2). Higher scores on the GCS are indicative of an increased level of consciousness. The total score is determined by adding the three sub scores. The total score can range from 3-15, with scores of 13-15 indicating a mild injury, 9-12 indicating a moderate injury, and 3-8 indicating a severe injury (Campbell 2000; Murdoch & Theodoros 2001). 

Duration of Loss of Consciousness

For moderate to severe TBI, the duration of LOC appears to be a valid measure of injury severity. LOC of less than 15 minutes, up to 6 hours, and between 6-48 hours represents a mild, moderate, and severe injury, respectively. When LOC exceeds 48 hours, the injury is considered very severe (Campbell 2000). 

Post-Traumatic Amnesia

PTA is the time period post trauma for which the conscious patient has no recall for events. PTA is formally defined as the period following emergence from coma in which the patient may appear confused, disoriented, or agitated (Campbell 2000). Research indicates a dose-response relationship, with the length of PTA frequently being proportional to the severity of injury. Injury severity is defined as mild if the duration of PTA is less than 1 hour, moderate if between 1–24 hours, and severe if PTA is between 1–7 days. PTA exceeding 7 days is considered to represent a very severe injury (Campbell 2000; Russell 1932). 

Table: Definitions of Injury Severity

Mild:

PTA < 1 hour

GCS 13-15

LOC < 15 minute

Moderate:

PTA 1-24 hours

GCS 9 – 12

LOC < 6 hours

Severe:

PTA 1 – 7 days

GCS between 3 – 8

LOC 6-48 hours

Very Severe:

PTA > 7 days

LOC > 48 hours