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The New Injury Severity Score Is a Better Predictor of Extended Hospitalization and Intensive Care Unit Admission Than the Injury Severity Score in Patients With Multiple Orthopaedic Injuries

Balogh, Zsolt J.; Varga, Endre; Tomka, János; Süveges, Gábor; Tóth, László; Simonka, János A.

Journal of Orthopaedic Trauma:
Original Articles
Abstract

Objective: To compare the scoring efficacy of the injury severity score (ISS) and the new injury severity score (NISS) in predicting extended hospital length of stay (LOS) and intensive care unit (ICU) admission and to determine the effect of multiple orthopaedic injuries (MOI) on the discrepancies between the ISS and NISS and their impact on extended LOS and ICU admission.

Design: Prospective cohort study.

Setting: Level 1 university trauma center.

Patients: All consecutive trauma admissions during the 2-year period ending on December 31, 2000, with age older than 14 years and survival greater than 24 hours were entered into the study.

Main Outcomes: Extended (≥10 days) hospital LOS and ICU admission.

Results: Of 3,100 patients, 7.5% had a higher NISS than ISS, spent more days in the hospital (22 versus 8; P < 0.001) and in the ICU (3.4 versus 0.1; P < 0.001), and had a higher mortality rate (8% versus 1.2%; P < 0.001) than patients with identical NISS and ISS. The NISS was found to be more predictive of longer (≥10 days) LOS (receiver operating characteristic [ROC] NISS = 0.794, ISS = 0.782; P < 0.0001) and ICU admission (ROC NISS = 0.944, ISS = 0.918; P < 0.0001). The multivariate predictive model including NISS showed a better goodness of fit compared with the same model that included ISS. Patients with discrepant scores (NISS > ISS) spent a longer time in the hospital and in the ICU in addition to having an increased frequency of ICU admission. In 61% of the cases, MOI were responsible for the discrepant (NISS > ISS) scores.

Conclusions: MOI have a significant effect on trauma outcomes such as LOS and ICU admission. The recognition of this high-risk group is not possible using the traditional ISS alone from retrospective or prospective databases. Considering its easier calculation and better predictive power, it is suggested that the NISS should replace the traditional ISS in trauma outcome research.

Scores of tissue injury are robust predictors of major trauma outcome measures, such as mortality and postinjury multiple organ failure (MOF). 1,2 The most frequently used anatomic measure, the injury severity score (ISS), has several inadequacies despite numerous modifications. 3,4 The ISS is defined as the sum of the squares of the single highest injury score in each of the three most severely injured body regions. 3 As such, the ISS fails to consider the second most severe injury from the already coded region in favor of less severe injuries that occur in other body regions. 4 The ISS also underestimates multiple orthopaedic injuries (MOI) in polytrauma scenarios and has been found to be a poor predictor of postinjury hospital length of stay (LOS). 5,6 Lastly the unnatural division of the human body into regions complicates calculations and diminishes the predictive power. 7

Despite its limitations, the ISS has been used extensively in trauma outcome research all over the world. Recently, believing that the ubiquitous nature of the ISS makes any improvement in its predictive power worthwhile, the new ISS (NISS) was introduced. 7 It is based on the sum of the squares of the three most severe injuries regardless of the body region. This simple modification makes calculation easier and improves mortality prediction. Meanwhile, the fundamentals of the coding, the Abbreviated Injury Scale (AIS), are preserved. The new score accounts for the most severe injuries, and by omitting the body regions from the calculation, it considers the more significant second and third lesions from the same area. This characteristic is especially important in penetrating injuries and polytrauma. The improved predictive power of the NISS compared with the ISS has been demonstrated in mortality and MOF prediction. 1,7–9

The objectives of our study were to compare the scoring efficacy of the ISS and the NISS in predicting extended hospital LOS and intensive care unit (ICU) admission and to determine the effect of MOI on the discrepancies between the ISS and NISS and their impact on extended LOS and ICU admission. It was hypothesized that the AIS extremity region would have a higher impact on the discrepancies between the NISS and the ISS than the other regions; in other words, MOI are a major cause of extended LOS and ICU admission.

Author Information

Department of Traumatology, Albert Szent-Györgyi Medical and Pharmaceutical Center, University of Szeged, Szeged, Hungary

Accepted April 6, 2003.

This study was presented at the 14th Annual Meeting of the Orthopaedic Trauma Association, San Diego, CA, October 20–22, 2001.

No financial support was received for this study. The authors received nothing of value.

This article does not contain information about medical devices.

Correspondence and reprints: Zsolt J Balogh, MD, Department of Traumatology, Albert Szent-Györgyi Medical and Pharmaceutical Center, University of Szeged, 6 Semmelweis Street, Szeged, Hungary, H-6725. E-mail: balogh@trauma.szote.u-szeged.hu.

© 2003 Lippincott Williams & Wilkins, Inc.