What is AIS (Abbreviated Injury
Scale) ?
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AIS is a scale that describes an injury in terms of anatomical position, specific kind and relative severity.
AIS has been developed to provide researchers with a simple numerical method for scaling and comparing injuries according to their severity and for standardizing the terminology used to describe them.
In the first place, AIS is based on the anatomical injuries and, in this respect, it differs from other systems related on physiological parameters. As a result of this principle there is but one unique AIS index for each injury in any given person, whereas in classifications related to physiological aspects there can be several indexes, depending on changing physiological conditions of each patient, for the same kind of injury, over a period of time.
Secondly, AIS establishes an index of injuries, not of their consequences. In improving AIS, the direct consequences of certain injuries have been reintroduced as part of certain injury description in order to define the injury itself more precisely.
Also, AIS is the foundation for I.S.S. (Injury Severity Score) to assess the overall severity of a poly-traumatized patient.
The origin of AIS
Under the joint sponsorship of the American Medical Association, the Association for the Advancement of Automotive Medicine (formerly American Association of Automotive Medicine) and the Society of Automotive Engineers, a committee representing said specialization, assisted by about 35 consultants, drafted the first version of the
Abbreviated Injury Scale, published in 1971.
This first version was followed by others, including the 1990 version still "in force" now. Each edition represents a revision of the previous one, depending on medical progress and based, in any case, on the observations and remarks from all those using AIS worldwide.
The copyright and the right of development of AIS and I.S.S. belong to AAAM (Association for the
Advancement of Automotive Medicine), with offices in Illinois, USA, who spread the scale by holding courses against payment of an enrollment fee all over the U.S. and, exceptionally, in the U.K.
Thanks to those courses, the AIS methodology has been spread throughout the U.S., in Northern Europe, Australia and Asia.
Since 1999 , for the first time in the history of AIS, teachers who will conduct AIS courses in a language other than English are being trained in Italy, so that courses in Italian language can be held directly in this country.
Aims of AIS
Initially, AIS was developed to be used for research into road accidents involving motor vehicles, in order to standardize the data on frequency and severity of the resulting injuries. The 1971 edition of AIS, although elementary in its structure, became the standard means for groups investigating into road accidents, funded by the US Department of Transportation as well as by other university-based teams or car-makers in the U.S., in Europe and in Australia.
Its application has been extended to include epidemiology, research performed in trauma-centers to predict the probability of survival, evaluation of a patient's clinical response, research into the sanitary system and assessment of the social costs of injuries.
The increased sophistication in the injury description (the present edition includes over 4000 definitions) has promoted an ever increasing use of AIS for data collection: if the first versions of AIS were fit to treat large quantities of data related to road accidents, the most recent versions can be used for research into quite different subjects. For that reason, AIS is now adopted worldwide, making comparative studies on any kind of injury easier.
It is thanks to its characteristics that AIS has become a tool of classification, inquiry and report particularly useful in Trauma Centers and Trauma Registers, as in the US they are considered an essential requisite for their qualification as such. Supposing, for instance, that we want to examine the evolution of a certain sector of traumatology over a period of time (due to accidents at work or due to road accidents), we could find this kind of data:
number of traumatized persons in the year X: 2,300
number of traumatized persons in the year X+ 5: 2,350
In this form, the numbers indicate nothing about the real evolution of the phenomenon as to the severity of the injuries, unless going into details for single injuries, individually indicated and entered into a table that would be most analytical and, therefore, long and confusing.
On the contrary, if the data are collected according to the AIS methodology right from the start, the following scheme can be easily obtained:
It shows the extremely different distribution of the severity of injuries in the periods taken into account, starting from the lowest level (AIS 0) up to the highest (AIS 6).
Far from excluding other methods of classification like ICD9, ICD10 or DRG or others used in emergency or therapy centers, AIS integrates these methods designed for aspects different from those of AIS.
Structure of AIS
The Abbreviated Injury Scale (AIS) is a system - based upon anatomy and fruit of the consensus of experts - designed to classify injuries according to the body region on an ordinal scale of severity starting from value AIS 1 (lowest level) up to value AIS 6 (presently without possibility of treatment). AIS does not assess the combined effects of multiple injuries.
Instead, the Injury Severity Score (ISS) elaborated by Bakers, defines the overall severity of injuries in poly-traumatized patients. The ISS index is the total of the squares of the highest AIS values in three different body regions.
The AIS methodology envisages the use of a "dictionary", that reports injuries one by one, according to the scheme shown ahead. There are specific rules inside the dictionary itself by which some classification quandaries can be solved, as for instance, a number of possible descriptions of an injury or several body regions to which the injury can be ascribed, and it suggests when the clinical diagnosis can be used. Synonyms or descriptions in brackets are used frequently to allow the codifier to match, in the best possible way, the description of the injury resulting from the medical record, with the description according to the AIS dictionary. These coding rules, together with the coder training and experience, determine the work's reliability both as far as each coder is concerned and as regards the relationship between people acting in different fields.
For that reason it is important that AIS is taught by qualified trainers and that the coding methodology is followed strictly.
This makes AIS a "universal, unequivocal language" used by all researchers, scholars and experts in traumatology.
In the AIS dictionary, each injury description is assigned a unique 6-digit numerical code, followed by the AIS code indicating the severity of the injury.
As shown in the scheme below, the first digit identifies the "body region", the second one identifies the anatomic region; the third and fourth digits identify the specific anatomical structure or, in case of injuries to the external region, the specific nature of injury; the fifth and sixth digits identify the level of injury within a specific body region and a specific anatomical structure. The digit to the right of the decimal point is the AIS scale for the severity of the
injury.
Click here to visualize (in italian)
an example of how a page of the AIS dictionary is structured; the example illustrates the coding of some injuries in the "head" region.
Conclusion
Please, note that the assignment of a description in the dictionary and, subsequently, of the corresponding AIS code must be supported by precise evidence such as diagnostic-instrumental diagnosis (Rx, TAC, etc.), surgical or post-mortem reports etc. That is to say, a diagnosis that merely considers the possibility of injuries cannot be taken into account; the traumatic injury must be observed and assessed in its real evidence.
The injuries data collection can be hindered by problems due to the type of scale applied, or by the quantity of information available to the coder or, finally, by the coder himself, that is the person who has to assign that code.
Therefore, we stress once more that AIS should be used only after serious training conducted by teachers authorized by AAAM. This association owns the exclusive copyright of the AIS and it is in a position to guarantee the observance of AIS "philosophy" and its application principles. In fact, the accurate and consistent application of AIS is essential to any serious injury data
collection.
