Injury Severity Score (ISS)

ISS body regions

The Injury Severity Score (ISS) evaluates trauma severity through the AIS classification of multiple injuries.

This trauma severity coding has been put in use by Baker in 1974 and allows a tracking of the most serious injuries in the six areas of the body.

ISS scores above 15 define major trauma/ polytrauma. The injury severity scale is known to provide a linear correlation with trauma hospitalisation, mortality and morbidity.

The trauma system continues to be updated, with the AIS Committee of the Association for the Advancement of Automotive Medicine (AAAM) being the current responsible authority.

The six body regions that are evaluated separately are:

■ Head and neck – this region also includes injuries to cervical spine.

■ Face – this includes facial skeleton, nose, mouth, eyes and ears.

■ Thorax – this includes chest injuries to rib cage, thoracic spine and diaphragm.

■ Abdomen – includes abdominal organs and lumbar spine.

■ Extremities - includes pelvic skeleton injuries and sprains, fractures, dislocations.

■ External and other – include injuries such as lacerations, contusions, burns, hypothermia.

The ISS was praised for the fact that it helps provide an accurate description of the severity of the injuries sustained.

By comparison, other trauma scoring systems, such as the Revised Trauma Score provide only a general understanding of the overall patient status.

The AIS code and ISS formula

The Abbreviated Injury Scale dates from 1969, however, has been updated in time to provide accurate survival prognosis.

Medical professionals who want to evaluate patients with multiple trauma require training under a Quality Assurance programme before they can allocate AIS codes.

As an anatomic severity scoring system, AIS evaluates and classifies an injury in any body region on a six point ordinal scale, where minor injuries are awarded 1 point and deadly injuries are given 6 points.

This is the current classification:

■ Minor (1 point);

■ Moderate (2 points);

■ Serious (3 points);

■ Severe (4 points);

■ Critical (5 points);

■ Maximal (incompatible with life) (6 points).

The ISS accounts for the three most severely injured body regions. When there are multiple injuries in the same body region, the most severe one is used in the score.

In order to obtain the overall ISS, the scores from the three regions with the highest scores are squared and summed.

ISS values range from 0 to 75 and can be obtained through numerous combinations of scores.

It is important to note that if a region is awarded an AIS of 6, regardless of the situation in the remaining body regions, the overall score is automatically 75 as the injury is deemed incompatible with life.

Because of the type of scoring method, any error occurring during AIS evaluation, is multiplied in the final ISS.

A criticism received by the model is the fact that it is not very specific (does not provide a weighing system) in the case of multiple injuries in the same body region.

Example of ISS calculation

Taking the case of a multiple injury patient who is brought to ER following a motor accident, the physical examination reveals the following:

The three most severely injured regions are: abdomen, face and thorax. The score for the abdomen will be considered 5 because is the highest between 3 and 5.

Therefore, the ISS is = 5² + 3² + 2² = 25 + 9 + 4 = 38 (out of 75 possible)

Original source

Baker SP, O'Neill B, Haddon W Jr, Long WB. The injury severity score: a method for describing patients with multiple injuries and evaluating emergency care. J Trauma. 1974; 14(3):187-96.

Other references

1. Copes WS, Champion HR, Sacco WJ, Lawnick MM, Keast SL, Bain LW. The Injury Severity Score revisited. J Trauma. 1988; 28(1):69-77.

2. Schluter PJ. The Trauma and Injury Severity Score (TRISS) revised. Injury. 2011; 42(1):90-6.