Does the New Injury Severity Score (NISS) Outperform the Injury Severity Score (ISS) for Predicting Mortality Among Blunt Trauma Patients in a Conflict-Affected Setting?

Trauma is a leading global cause of morbidity and mortality, particularly among individuals under 40 years of age, accounting for approximately 5 million deaths annually. To address the challenges of assessing trauma severity, tools like the Injury Severity Score (ISS) and the New Injury Severity Score (NISS) have been developed to predict patient outcomes, including mortality. The ISS, introduced in 1974, is based on the Abbreviated Injury Scale and evaluates the three most severely injured body regions. However, it has limitations, including its inability to account for multiple injuries in the same body region. To overcome these, the NISS was introduced in 1997, summing the squares of the three most severe injuries, irrespective of location, potentially offering improved predictive accuracy in certain trauma populations.

The predictive accuracy of ISS and NISS has been extensively studied, with mixed findings. Meta-analyses and cohort studies suggest both tools are effective, with NISS often demonstrating slightly superior sensitivity and area under the curve (AUC) for mortality prediction. For instance, one analysis reported an AUC of 0.9095 for NISS versus 0.9009 for ISS in predicting mortality. While both tools are considered reliable, NISS's ability to account for multiple severe injuries within the same region makes it particularly advantageous in cases of polytrauma.

Despite these advances, significant heterogeneity exists among studies, largely due to differences in trauma mechanisms, patient populations, and study methodologies. For instance, blunt versus penetrating trauma and age-related factors can influence the tools' performance. Additionally, the lack of standardized reporting and quality assurance in scoring further complicates comparisons, highlighting a need for more uniform research protocols.

In Iraq, where trauma from road traffic accidents and violence is prevalent, evaluating the predictive utility of ISS and NISS is particularly important. Despite the global use of these tools, limited data exists on their effectiveness in Middle Eastern populations, where differences in healthcare infrastructure and injury patterns may affect performance. This study aims to address this gap by comparing the mortality predictive abilities of ISS and NISS in an Iraqi trauma population. Understanding their relative effectiveness in this context could inform better resource allocation, improve trauma care, and guide future research tailored to local needs.