Emergency Medical Services/Original Research
Optimal defibrillation response intervals for maximum out-of-hospital cardiac arrest survival rates*,**,,*

Presented in part at the Society for Academic Emergency Medicine annual meeting, Boston, MA, May 1999.
https://doi.org/10.1067/mem.2003.266Get rights and content

Abstract

Study objective: Many centers optimize their emergency medical services (EMS) systems to achieve a target defibrillation response interval of “call received by dispatch” to “arrival at scene by responder with defibrillator” in 8 minutes or less for at least 90% of cardiac arrest cases. The objective of this study was to analyze survival as a function of time to test the evidence for this standard. Methods: This prospective cohort study included all adult, cardiac etiology, out-of-hospital cardiac arrest cases from phases I and II of the Ontario Prehospital Advanced Life Support (OPALS) study. Patients in the 21 Ontario study communities received a basic life support level of care with defibrillation by ambulance and firefighters but no advanced life support. Survival was plotted as a function of the defibrillation response interval. The equation of the curve, generated by means of logistic regression, was used to estimate survival at various defibrillation response interval cutoff points. Results: From January 1, 1991, to December 31, 1997, there were 392 (4.2%) survivors overall among the 9,273 patients treated. The defibrillation response interval mean was 6.2 minutes, and the 90th percentile was 9.3 minutes. There was a steep decrease in the first 5 minutes of the survival curve, beyond which the slope gradually leveled off. Controlling for known covariates, the decrement in the odds of survival with increasing response interval was 0.77 per minute (95% confidence interval 0.74 to 0.83). The survival function predicts, for successive 90th percentile cutoff points, both survival rates and additional lives saved per year in the OPALS communities compared with the 8-minute standard: 9 minutes (4.6%; −18 lives), 8 minutes (5.9%; 0 lives), 7 minutes (7.5%; 23 lives), 6 minutes (9.5%; 51 lives), and 5 minutes (12.0%; 86 lives). Conclusion: The 8-minute target established in many communities is not supported by our data as the optimal EMS defibrillation response interval for cardiac arrest. EMS system leaders should consider the effect of decreasing the 90th percentile defibrillation response interval to less than 8 minutes. [Ann Emerg Med. 2003;42:242-250.]

Introduction

Forty years ago, in the original description of closed-chest cardiopulmonary resuscitation (CPR), Kouwenhoven et al1 emphasized the importance of timely defibrillation: “External defibrillation is not likely to be followed by the return of spontaneous heart action, unless the counter-shock is applied in less than three minutes after the onset of ventricular fibrillation.” Since then, the role of rapid defibrillation in the survival of victims of out-of-hospital cardiac arrest has endured the test of a battery of retrospective analyses,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 and recently, it has been validated as an independent predictor of survival in a large, prospective clinical trial.16, 17 Many systems have adopted an 8-minute standard as a targeted defibrillation response interval of “call received by dispatch” to “arrival at scene by responder with defibrillator” in at least 90% of cardiac arrest cases. However, there is little evidence to support 8 minutes as a suitable, let alone optimal, criterion.

The objective of the current investigation is to analyze survival as a function of time to test the evidence for the 8-minute standard. This investigation is a substudy of the ongoing Ontario Prehospital Advanced Life Support (OPALS) study.18 The OPALS study is the largest out-of-hospital investigation yet conducted. With 21 communities and more than 10,000 patients with cardiac arrest, this study provides a unique opportunity to further elucidate the cardiac arrest picture and to generate hypotheses for future study. The study uses a before-and-after clinical trial design to test the incremental benefit of the addition of rapid defibrillation and advanced life support to an existing basic life support system. Within this framework, we conducted an observational cohort study to examine the relationship between response intervals and cardiac arrest survival. The data cover the time before the implementation of advanced life support in the OPALS study.

Section snippets

Materials and methods

The OPALS study involves 21 Ontario urban-suburban study communities that have been identified within the response areas of 11 emergency medical services (EMS) base hospital programs. According to 1991 census data, the combined population served in these 21 centers is 2,815,000. Study community base populations range from 16,000 to 750,000. Ambulance services in these centers respond to more than 120,000 code 4 (highest priority) calls each year. In the study sites, EMS responds to

Results

From January 1, 1991, to December 31, 1997, there were a total of 9,969 cardiac arrest cases in the 21 OPALS study communities. The 696 (7.0%) cases that were EMS witnessed were excluded from this analysis.

Table 1 identifies the patient and EMS characteristics of the remaining 9,273 patients that are the subject of this study.

. Patient and EMS system characteristics.

CharacteristicPatients (N=9,273)
Mean age, y (SD) (n=9,134)68.3 (13.8)
Male sex, No. ( %) (n=9,267)6,269 (67.7)
Bystander-witnessed

Discussion

Pursuing a reduction in the out-of-hospital defibrillation response interval is a key optimization strategy for improving cardiac arrest survival within a community. However, our data indicate that the 8-minute target currently adopted by many EMS systems does not represent sufficient optimization. Rather, it is clear that significant survival gains can be attributed to decreasing the defibrillation response interval well below 8 minutes. The 8-minute mark is not accompanied by any dramatic

Acknowledgements

We thank the OPALS Study Group investigators from the following base hospital programs: Burlington, Ontario, Canada: Matthew W. Stempien, MD, CCFP(EM), Carrie I. Parkinson, RN, BScN; Cambridge, Ontario, Canada: David Waldbillig, MD, CCFP(EM), Kieran W. Ballah, EMCA; Kingston, Ontario, Canada: Gordon J. Jones, MD, FRCPC, Mark R. Halliday, EMCA; London, Ontario, Canada: Jonathan F. Dreyer, MDCM, FRCPC, Kenneth A. Boyle, EMCA, EMT; Niagara, Ontario, Canada: Douglas P. Munkley, MD, MCFP(EM),

References (25)

Cited by (169)

View all citing articles on Scopus
*

Dr. Stiell holds a Distinguished Investigator Award from the Canadian Institutes of Health Research.

**

Supported by peer-reviewed grants from the Emergency Health Services Branch of the Ontario Ministry of Health and Long-Term Care and the Canadian Health Services Research Foundation.

Reprints not available from the authors.

*

Author contributions: VDM, IS, and GW conceived the study and designed the study. IS and GW obtained research funding. VDM, IS, and GW supervised the conduct of the study and data collection. VDM and IS managed the data. VDM, GW, and IS provided statistical advice on study design and analyzed the data. VDM drafted the manuscript, and all authors contributed substantially to its revision. VDM takes responsibility for the paper as a whole.

View full text