Comparing Exponential Injury Severity Score (EISS) With Injury Severity Score (ISS) and New Injury Severity Score (NISS)

Trauma is defined as a physical injury from an external source of sudden onset and severity, which require immediate medical attention. Polytrauma is a short verbal equivalent commonly used for severely injured patients usually with associated injury (i.e., two or more severe injuries in at least two different areas of the body), less often with a multiple injury (i.e., two or more severe injuries in one body area). Polytrauma patients usually have a much higher risk of mortalities and disabilities than the risk of expected mortalities in individual injuries patients.

Despite improvements in trauma systems worldwide, trauma continues to be one of the leading causes of death and disability in all age groups, especially the young and middle age group. Approximately 5.8 million people die each year due to trauma related injuries, representing 8% of the worldwide mortality.

For studying the outcomes of trauma, accurate and reliable methodological tools are required for appropriate scoring of severity and outcome prediction.

Trauma scores were designed to facilitate the triage of patients in the Emergency Room (ER) and identify patients with Polytrauma with low chances of survival. Those scores were meant to organize and improve the quality of trauma care systems, and to assess resources allocation.

Trauma patients present to the emergency department (ED) with a great variety of injuries and diseases. To address these, the Abbreviated Injury Scale (AIS) system defines the severity of injury throughout the different regions of the body. It is an anatomically based, consensus derived, global severity scoring system that classifies an individual injury by body region according to its relative severity on a 6-point scale (1 = minor and 6 = maximal). The system is constantly revised, expanded, and improved, and the Association for the Advancement of Automotive Medicine recently announced its latest revision, the AIS 2005-Update 2008 and AIS 2015. To summarize a single patient's multiple injures into a single score, the Injury Severity Score (ISS) was created by Baker et al. in 1974, which has been considered the "gold standard" among anatomic injury severity indicators. It is based on the AIS severity values, that is, the summation of the squares of the severity digit in the AIS of the most severe injuries, in three of six predefined body regions.

However, the ISS only includes one injury in each body region, which leads to possible inclusion of a less severe injury in other body regions rather than another serious injury in the same body region. To overcome this limitation, a modified ISS, the New Injury Severity Score (NISS) was introduced by Osler et al. in 1997. NISS is simply the sum of squares of the three most severe injuries, regardless of the body regions injured.

Further, Wang et al. have created the Exponential Injury Severity Score (EISS) in 2014 by modifying the AIS system. The EISS was computed as the simple change in AIS values by raising each AIS severity score (1-6) by 3 taking a power of AIS minus 2, and then summing the three most severe scores (i.e., highest AIS values), regardless of body regions. With this exponential transformation of the AIS values, the EISS is expected to be more reflective of the true severity of injuries in a patient with polytrauma. In Wang's study, the EISS is reported to be more predictive of survival; therefore, it might be used as the standard summary measure of human trauma.