Injury Severity Score

aka ISS

Principle means of predicting trauma outcome

  • Computed from Abbreviated Injury Scale (AIS) scores associated with individual injuries which range from 1 to 6
  • ISS defined as “the sum of the squares of the highest AIS grade in the three most severely affected areas” – because 6 is nearly always fatal the scale therefore goes from 0 to 75

There are six areas in the ISS

  1. Face
  2. Head & neck
  3. Chest
  4. Abdomen & pelvic contents
  5. Bony pelvis & limbs
  6. Body surface

The AIS90 dictionary is used to score every injury & the ISS then calculated

There are several shortcomings:

  • Based on the highest AIS score among the injuries in a particular body region – thus it may underestimate the severity of the condition in the patients with multiple injuries in one or more body regions
  • Diverse injury combinations with distinct survival probabilities can have the same or nearly the same ISS values – e.g. isolated severe head injury AIS=5: ISS=25 given same weighting as abdominal injury (eg liver laceration) AIS=4: ISS=16 + extremity injury (eg open radius fracture) AIS=3: ISS=9
  • ISS gives same weighting to injuries with the same AIS severity in different body regions