of the injury; the physiological response of the body to the injury; and a priori or host factors such as age, gender, and coexisting disease that mediate the response of the body to the injury. There is general consensus that all four indicators or parameters are important for characterizing the impact of an injury or a constellation of injuries on outcome. More research is needed to improve the measurement of each parameter and to develop better models that establish the relationship between these parameters and outcomes, as discussed below.

The Abbreviated Injury Scale (AIS) has become a standard for measuring the extent of tissue damage (AAAM, 1990), yet its usefulness in detailed clinical studies of trauma involving specific organ systems is limited. Other classifications have been developed, such as to classify solid organ injuries (Moore et al., 1995) and long-bone fractures (Muller et al., 1990). The harmonization of these classifications should be encouraged. The AIS rates the severity of single injuries only. The Injury Severity Score (ISS) (Baker and O'Neill, 1976), defined as the sum of the squares of the maximum AIS obtained in each of the three most severely injured body regions, is currently the most widely used method for assessing the combined effect of multiple injuries. However, recent work has pointed to inadequacies of the ISS (Copes et al., 1988; Cayten et al., 1991). Alternatives such as the Anatomic Profile (Copes et al., 1990) and the New Injury Severity Score (Osler et al., 1997) have been proposed in order to account more adequately for the severity of multiple injuries to a single body system and for the important contribution of head injury in predicting outcome. These newer methods must be evaluated more broadly before their widespread use.

For large, population-based studies, use of the AIS (and its derivatives for scaling multiple injuries) is often not practical, since it takes, on average, between 10 and 20 minutes to score a single patient. Alternative scoring systems based on the International Classification of Diseases (ICD) have been proposed (MacKenzie et al., 1989; Rutledge et al., 1997). Although not as detailed a classification as the AIS, the clinical modification of the Ninth Revision of the ICD (ICD-9CM) does provide an alternative set of anatomic descriptors that is useful for characterizing the nature of traumatic injuries. Given the widespread use of the ICD, the further development and evaluation of ICD-based scoring systems should receive high priority.

The Revised Trauma Score (RTS)—based on the Glasgow Coma Score, systolic blood pressure, and respiratory rate—is the most widely used measure of injury severity based on physiologic parameters (Champion et al., 1989b). Although it has been shown to be a good predictor of mortality when combined with age and mechanism of injury, the RTS is inaccurate when the patient either is under the influence of drugs or alcohol or is intubated, paralyzed, or both (Offner et al., 1992). In addition, RTS values fluctuate over time and are sensitive to prehospital treatment. Further work is needed to better understand how these factors affect RTS values and how this information can be used to identify which values obtained over the course of time and treatment should be used retrospectively as fixed-point indicators of severity. In addition, further research

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