Trauma scores are widely used to quantify severity of injury of trauma patients for research and audit purposes.
With increasing use of CT for evaluation of major trauma,
radiologists play a crucial role in supporting accurate trauma scoring.
Unfortunately,
most have no idea this is the case.
The Injury Severity Score (ISS) is an anatomical score,
derived from the Abbreviated Injury Scale (AIS) that is concerned with injuries to the 6 body areas below and was first described by Susan Baker in 1974.
- Head and neck
- Face
- Chest
- Abdomen
- Pelvis and extremities
- Skin
Each injury receives an AIS of 0-5,
with 0 being uninjured,
1 trivial/minor through to 5 which is extremely severe.
This AIS is converted into the ISS by adding together the square of the three highest-scoring injuries from three highest-scoring body regions (i.e.
only one injury per body region is included).
Thus,
the ISS may range from 0 to a maximum of 75 (3 x 52) .
An ISS of 16 or more is typically regarded as "major trauma" and an ISS >40 as "massive trauma".
Injuries are scored from clinical examination findings,
radiological investigations,
or at post mortem.
The primacy of CT as the imaging modality of choice in major trauma means that CT reports are the principal source from which trauma scores are calculated,
but few UK and European radiologists have knowledge or experience of trauma scoring.
The ISS for individual cases forms part of the data record in the UK's national Trauma Audit and Research Network (TARN).
Injury Severity Scores form the major part of TARN's Predicted Survival Score (PSS) which is used to assess whether individual hospitals have more or fewer trauma survivors than expected.
This data is used as a tool to directly compare the "performance in major trauma care" of one hospital against another.
An earlier study at our institution found that post-mortem reports were insufficiently precise to calculate an accurate ISS to trauma fatalities.
This could lead to the under-scoring of injuries and hence give the impression that patients have died from injuries that their PSS suggests "should" have survived.
We wondered if the same applied to CT reports: are conventional,
free-text CT reports sufficiently precise to calculate a reliable ISS? And if not,
do ISS calculated from conventional free-text CT reports cause under or over-scoring of the AIS? If the former,
hospitals' "trauma performance" may be under-rated and if the latter,
vice versa.