Is There A Golden Hour in Combat Casualty Evacuation?

Abstract

University of Washington Abstract Is There A Golden Hour in Combat Casualty Evacuation? Joint Theater Trauma Registry 2003 to 2011 Scott H. Robinson Chair of the Supervisory Committee: Professor Joel D Kaufman Department of Environmental and Occupational Health Sciences Background In the late 1960s and early 1970s it was asserted that the most critical aspect of trauma care was early arrival to surgical care, especially within the first sixty minutes after injury. This presumed relationship between time and mortality became popularly known as "The Golden Hour", and has driven Emergency Medical System (EMS) organization since. In robust civilian Emergency Medical Services trauma transport and treatment systems, large studies are now showing that there is no relationship between relative increases in total pre-hospital time and mortality. These new surprising and robust results contradict the conceptual framework that drove the development of rapid response EMS systems in our nation and across the globe. Purpose The purpose of this study is to test the hypothesis that there is a relationship between total out of hospital time and mortality in the US military combat casualty care system, especially whether there is a "Golden Hour". We did this using data from the main data collection on casualty care and outcome within the military, the Joint Theater Trauma Registry, with the secondary aim of informing improvements to this data collection system. Methods The Joint Theater Trauma Registry collects data primarily at the point of surgical care on patients evacuated to and treated at a theater surgical hospital. A data set of all patients with a known value for total pre-hospital time was requested and provided to the researchers. Data was available on evacuations occurring between 2003 to early 2012. Using logistic regression, adjusted odds ratios were calculated for the association of total out of hospital time and mortality. We also report adjusted odds ratios and p values for multiple other descriptors of interest. Results We found lower in-hospital mortality among casualties with longer pre-hospital time. Using a time variable grouped by 20 minute intervals, we determined an odds ratio of 0.890 (95% CI of 0.823 to 0.963) for mortality trend associated with increasing pre-hospital time. Testing for interaction between Injury Severity and increasing prehospital time revealed a magnification of this protective effect. Casualties arriving with an Injury Severity Score (ISS) score of between 16-50 had a 1.3 times greater survival with prehospital times greater than sixty minutes as compared to those with less than sixty minutes, and the same comparison for patients with ISS scores of 51 or greater yielded a four fold higher survival. Conclusion In-hospital mortality is significantly lower for patients with longer pre-hospital times, and this effect is magnified for patients with greater injury severity. This observation may be explained by selection out of the group available for analysis, or due to more rapid evacuation of the most seriously injured but survivable injuries. Overall, rather than testing the golden hour hypothesis, our findings likely represents a winnowing effect, in which longer pre-hospital times and greater injury severity result in death during the pre-hospital period.