ABSTRACT Objective. Air medical transport programs have been in existence for two decades. During this time, no outcome measures have been developed for these services. The authors examined severity scoring and mortality data from their air medical service to characterize its performance and to identify trends in acuity and mortality over a 15-year peri- od. Methods. APACHE-II scores derived at the time of transport and hospital mortality data have been concurrent- ly recorded in the flight database for adult transports since 1986. The authors analyzed these data and examined the correlation between APACHE-II score at the time of trans- port and hospital mortality for the 15-year period 1986–2001. Results. 13,808 adult transports were identified. APACHE data were available for 8,204 patients (59%) and mortality for 10,845 (79%), respectively. The number of transports increased from 935 to 1,231 per year. Mean APACHE-II for all patients was 11.6 ± 8.4. Overall mortality was 22%. Both patient acuity and mortality were trending upward over time. The correlation between APACHE-II and mortality was close and linear (mortality = 0.018  APACHE-II – 0.0243, R 2 = 0.97). Conclusions. Both severity of illness and mortal- ity of air-transported patients appear to be increasing slow- ly over time in response to changes in the health care system. The strong correlation between APACHE-II performed at the time of transport and mortality validates this technique for benchmarking. The slope of this correlation is an out- come-based characteristic of system performance that may allow monitoring of a system over time and comparisons between systems. Key words: air ambulance; APACHE; hos- pital mortality; transportation of patients. PREHOSPITAL EMERGENCY CARE 2003;7:195–198 Although there has been increasing recognition of the importance of outcome measures in the study of health care delivery systems, the care provided by air medical transport services has not been consistently evaluated either quantitatively or qualitatively. A sim- ple first step toward this end is measurement of the severity of illness or injury among these patients, and examination of the relationship between severity and mortality in the patients wgi have been transported. Severity scoring systems assign points derived by regression analysis for abnormalities in physiologic measures, laboratory data, and patient history, and are used to predict mortality in patient populations. The Acute Physiology and Chronic Health Evaluation (APACHE) system for illness severity measurement was developed by Knaus et al. in 1981 1 and revised in 1985. 2 Physiologic severity scoring in patient transport using variants of the APACHE methodology was advocated and described by Bionet al. in 1985, 3 and then in the United States by Rhee et al. 4,5 Despite these early efforts, little has been written about characterizing severity of illness in air medical patient transport over the past decade and a half. We have kept consistent acuity statistics on all adult transports since 1986. We undertook the present study to address the following questions: 1) Has the acuity of transported patients changed over time? 2) Has the mortality rate of transported patients changed over time? 3) Is there a relationship between APACHE-II score and mortality in transported patients? 4) Can acuity and mortality measures be used to benchmark system performance? The overall goal was to examine the use of physiologic severity scoring and mortality data to identify trends in, and characterize the long- term performance of, our air medical system. ORIGINAL CONTRIBUTIONS Received July 19, 2002, from University of Michigan Departments of Emergency Medicine (RS, MJL, RFM) and Surgery (REB), and University of Michigan Survival Flight (KN, MS, MJL), Ann Arbor, Michigan. Revision received November 22, 2002; accepted for pub- lication November 25, 2002. Presented as a poster at the National Association of EMS Physicians annual meeting, Tucson, Arizona, January 2002. Address correspondence and reprint requests to: Robert Silbergleit, MD, Department of Emergency Medicine, UMMC TC B1354/0303, 1500 East Medical Center Drive, Ann Arbor, MI 48109-0303. e-mail: <robie@umich.edu>. LONG-TERM AIR MEDICAL SERVICES SYSTEM PERFORMANCE USING APACHE-II AND MORTALITY BENCHMARKING Robert Silbergleit, MD, Richard E. Burney, MD, Kris Nelson, RN, Michael Snyder, RN, Mark J. Lowell, MD, Ronald F. Maio, DO 195