Susan P. Baker

A method for comparing death rates of groups of injured persons was developed, using hospital and medical examiner data for more than two thousand persons. The first step was determination of the extent to which injury severity as rated by the Abbreviated Injury Scale correlates with patient survival. Substantial correlation was demonstrated. Controlling for severity of the primary injury made it possible to measure the effect on mortality of additional injuries. Injuries that in themselves would not normally be life-threatening were shown to have a marked effect on mortality when they occurred in combination with other injuries. An Injury Severity Score was developed that correlates well with survival and provides a numerical description of the overall severity of injury for patients with multiple trauma. Results of this investigation indicate that the Injury Severity Score represents an important step in solving the problem of summarizing injury severity, especially in patients with multiple trauma.

BAKER, SUSAN P. M.P.H.; O'NEILL, BRIAN B.Sc; HADDON, WILLIAM JR. M.D.; LONG, WILLIAM B. M.D. Author Information

* Associate Professor of Public Health Administration, Division of Forensic Pathology. The Johns Hopkins School of Hygiene and Public Health, Baltimore, Maryland. †Vice President for Research, Insurance Institute for Highway Safety, Washington, D. C.

OBJECTIVES: The Injury Severity Score (ISS) has served as the standard summary measure of anatomic injury for more than 20 years. Nevertheless, the ISS has an idiosyncrasy that both impairs its predictive power and complicates its calculation. We present here a simple modification of the ISS called the New Injury Severity Score (NISS), which significantly outperforms the venerable but dated ISS as a predictor of mortality. DESIGN: Retrospective calculation of NISS and comparison of NISS with prospectively calculated ISS. MATERIALS AND METHODS: The NISS is defined as the sum of the squares of the Abbreviated Injury Scale scores of each of a patient's three most severe Abbreviated Injury Scale injuries regardless of the body region in which they occur. NISS values were calculated for every patient in two large independent data sets: 3,136 patients treated during a 4-year period at the American College of Surgeons' Level I trauma center in Albuquerque, New Mexico, and 3,449 patients treated during a 4-year period at the American College of Surgeons' Level I trauma center at the Emanuel Hospital in Portland, Oregon. The power of NISS to predict mortality was then compared with previously calculated ISS values for the same patients in each of the two data sets. MEASUREMENTS AND MAIN RESULTS: We find that NISS is not only simple to calculate but more predictive of survival as well (Albuquerque: receiver operating characteristic (ROC) ISS = 0.869, ROC NISS = 0.896, p < 0.001; Portland: ROC ISS = 0.896, ROC NISS = 0.907,p < 0.004). Moreover, NISS provides a better fit throughout its entire range of prediction (Hosmer Lemeshow statistic for Albuquerque ISS = 29.12, NISS = 8.88; Hosmer Lemeshow statistic for Portland ISS = 83.48, NISS = 19.86). CONCLUSION: NISS should replace ISS as the standard summary measure of human trauma.