Emergency medical services/original research
Emergency Medical Services Intervals and Survival in Trauma: Assessment of the “Golden Hour” in a North American Prospective Cohort

Presented as an abstract at the Society for Academic Emergency Medicine Annual Meeting, May 2008, Washington, DC.
https://doi.org/10.1016/j.annemergmed.2009.07.024Get rights and content

Study objective

The first hour after the onset of out-of-hospital traumatic injury is referred to as the “golden hour,” yet the relationship between time and outcome remains unclear. We evaluate the association between emergency medical services (EMS) intervals and mortality among trauma patients with field-based physiologic abnormality.

Methods

This was a secondary analysis of an out-of-hospital, prospective cohort registry of adult (aged ≥15 years) trauma patients transported by 146 EMS agencies to 51 Level I and II trauma hospitals in 10 sites across North America from December 1, 2005, through March 31, 2007. Inclusion criteria were systolic blood pressure less than or equal to 90 mm Hg, respiratory rate less than 10 or greater than 29 breaths/min, Glasgow Coma Scale score less than or equal to 12, or advanced airway intervention. The outcome was inhospital mortality. We evaluated EMS intervals (activation, response, on-scene, transport, and total time) with logistic regression and 2-step instrumental variable models, adjusted for field-based confounders.

Results

There were 3,656 trauma patients available for analysis, of whom 806 (22.0%) died. In multivariable analyses, there was no significant association between time and mortality for any EMS interval: activation (odds ratio [OR] 1.00; 95% confidence interval [CI] 0.95 to 1.05), response (OR 1.00; 95% CI 9.97 to 1.04), on-scene (OR 1.00; 95% CI 0.99 to 1.01), transport (OR 1.00; 95% CI 0.98 to 1.01), or total EMS time (OR 1.00; 95% CI 0.99 to 1.01). Subgroup and instrumental variable analyses did not qualitatively change these findings.

Conclusion

In this North American sample, there was no association between EMS intervals and mortality among injured patients with physiologic abnormality in the field.

Introduction

The first 60 minutes after traumatic injury has been termed the “golden hour.”1 The concept that definitive trauma care must be initiated within this 60-minute window has been promulgated, taught, and practiced for more than 3 decades; the belief that injury outcomes improve with a reduction in time to definitive care is a basic premise of trauma systems and emergency medical services (EMS) systems. However, there is little evidence to directly support this relationship.1 Two studies from Quebec suggested that increased total out-of-hospital (ie, EMS) time was associated with increased mortality among seriously injured trauma patients,2, 3 yet this finding has not been replicated in other settings.4, 5, 6, 7, 8, 9, 10 Additional studies suggesting a link between out-of-hospital time and outcome have been tempered by indirect comparisons,11 small samples of highly selected surgical patients,12, 13, 14 rural trauma patients with long EMS response times,15 and mixed samples that included patients with nontraumatic cardiac arrest.16, 17

To date, patients with out-of-hospital cardiac arrest remain the only field-based patient population with a consistent association between time (response interval) and survival.18, 19 Despite the paucity of outcome evidence supporting rapid out-of-hospital times for the broader population of patients activating the 911 system, EMS agencies in North America are generally held to strict standards about intervals, particularly the response interval. Meeting such expectations requires comprehensive emergency vehicle and personnel coverage throughout a community and travel at high speeds in risky traffic situations (eg, intersections) that occasionally result in crashes causing injury and death to emergency vehicle occupants and others.20, 21, 22 Demonstrating the benefit of such time standards in noncardiac arrest patients is important in justifying the resources and risks inherent in meeting such goals in EMS systems. Previous studies assessing the time-outcome association in trauma have been limited by heterogeneous patient groups, single EMS agencies, small sample sizes, and the exclusion of patients who died in the field.

In this study, we tested the association between EMS intervals and mortality among trauma patients known to be at high risk of adverse outcomes (those with field-based physiologic abnormality) in 146 diverse EMS agencies across 10 North American sites. Patients who died in the field were also examined as a subset of this population.

Section snippets

Study Design

This was a secondary analysis of an out-of-hospital, consecutive-patient, prospective cohort registry of injured persons with field-based physiologic abnormality.

Setting

These data were collected as part of the Resuscitation Outcomes Consortium epidemiologic out-of-hospital trauma registry (the Resuscitation Outcomes Consortium Epistry-Trauma).23 The primary sample for this study was collected from December 1, 2005, through March 31, 2007. Eligible patients were identified from 146 EMS agencies (ground

Characteristics of Study Subjects

Of the 7,555 patients meeting Epistry inclusion criteria and transported to a hospital, there were 4,276 adult trauma patients transported by 146 EMS agencies to 51 Level I or II trauma centers during the 16-month period (Figure 1). After exclusion of patients with missing survival status (n=152), coenrollment in a concurrent clinical trial with embargoed outcomes (n=130), and missing or erroneous out-of-hospital times, locations, or other incomplete data (n=338), 3,656 adults with complete

Limitations

Previous studies have demonstrated an apparent association between increasing out-of-hospital time and decreased mortality (ie, the appearance that longer times decrease mortality),7, 8, 9, 10, 16 even after accounting for injury severity. This phenomenon is at least partly explained by EMS providers moving and driving faster for patients believed to have serious injury and spending more time on calls with patients recognized as having minor injury (ie, less urgency to get such patients to a

Discussion

In this study, we were unable to support the contention that shorter out-of-hospital times (as measured from receipt of 911 call to hospital arrival) improve survival among injured adults with field-based physiologic abnormality. This finding persisted across many subgroups, including level of first responding EMS provider, mode of transport, country, age, injury type, and more severe physiologic derangement. Our findings are consistent with those of previous studies that similarly have failed

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    Supervising editor: Daniel W. Spaite, MD

    Author contributions: CDN conceived of and designed the study. RS performed the database management, quality assurance of the data, and all statistical analyses. CDN, RS, JRH, JPT, DPD, EMB, and GN interpreted preliminary findings and assisted in refining the final analysis. CDN drafted the article, and all authors contributed substantially to its revision. RS takes responsibility for data quality and all analyses. CDN takes responsibility for the paper as a whole.

    Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article that might create any potential conflict of interest. See the Manuscript Submission Agreement in this issue for examples of specific conflicts covered by this statement. The Resuscitation Outcome Consortium was supported by a series of cooperative agreements to 10 regional clinical centers and 1 data coordinating center (5U01 HL077863, HL077881, HL077871, HL077872, HL077866, HL077908, HL077867, HL077885, HL077877, HL077873) from the National Heart, Lung, and Blood Institute, in partnership with the National Institute of Neurological Disorders and Stroke, US Army Medical Research and Material Command, the Canadian Institutes of Health Research-Institute of Circulatory and Respiratory Health, Defence Research and Development Canada, the Heart and Stroke Foundation of Canada, and the American Heart Association.

    Publication date: Available online September 22, 2009.

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