Modifiable Factors Associated With Improved Cardiac Arrest Survival in a Multicenter Basic Life Support/Defibrillation System: OPALS Study Phase I Results,☆☆,,★★,

Presented at the Society for Academic Emergency Medicine Annual Meeting, Washington DC, May 1997.
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Abstract

Study objectives: This study was conducted to identify modifiable factors associated with survival for prehospital cardiac arrest in a large, multicenter EMS system with basic life support/defibrillation (BLS-D) level of care. Methods: This observational cohort study constitutes Phase I of the 3-phase Ontario Prehospital Advanced Life Support (OPALS) Study. Included were all adults who had cardiac arrest before EMS arrival in 21 urban/suburban communities that operate under the jurisdiction of 1 ambulance services branch, have 911 telephone service, and provide ambulance defibrillation but no prehospital advanced life support (ALS). Central dispatch and ambulance records were reviewed according to the Utstein guidelines. Associations between multiple patient and EMS factors and survival to discharge were assessed by univariate then stepwise logistic regression analyses. Results: From January 1, 1991, to January 31, 1995, 5,335 eligible patients were treated. Of these, 46.8% of cardiac arrests were witnessed by citizens, 14.5% received bystander CPR, 25.6% received CPR by fire or police, and 38.2% had an initial rhythm of ventricular fibrillation/ventricular tachycardia (VF/VT). The mean interval from call received to vehicle stopped was 6.7 minutes. Survival was 3.5% overall and 8.8% for VF/VT. Multivariate analysis found the following factors to be independently associated with survival (odds ratio with 95% confidence intervals): age .81 (.73, .89), bystander-witnessed arrest 4.05 (2.78, 5.90), bystander CPR 2.98 (2.07, 4.29), CPR by fire or police 2.20 (1.46, 3.31), and response interval call received to vehicle stopped .76 (.71, .82). Conclusion: This represents the largest multicenter BLS-D study of prehospital cardiac arrest yet conducted and clearly indicates that patient survival may be improved by optimization of EMS response intervals, bystander CPR, as well as first-responder CPR by fire or police.

[Stiell IG, Wells GA, DeMaio VJ, Spaite DW, Field BJ, Munkley DP, Lyver MB, Luinstra LG, Ward R, for the OPALS Study Group: Modifiable factors associated with improved cardiac arrest survival in a multicenter basic life support/defibrillation system: OPALS Study phase I results. Ann Emerg Med January 1999;33:44-50.]

Section snippets

INTRODUCTION

Thirty years ago, Pantridge and Geddes1 introduced the concept of providing advanced cardiac life support (ACLS) care to cardiac arrest victims outside of hospitals with mobile intensive care vehicles in Belfast. Many European and North American EMS responders provide out-of-hospital defibrillation and in some cases intravenous drug therapy and advanced airway techniques to cardiac arrest victims. Despite these advances, cardiac arrest survival remains poor in most jurisdictions, ranging from

MATERIALS AND METHODS

Overall, the OPALS Study incorporates a multiphase before-after design with the unit of study being all eligible cardiac arrest patients seen during each of 3 distinct phases. The current study, phase I, represents an observational cohort study conducted from 1991 through 1994 when all communities provided an ambulance automated defibrillation (BLS-D) program. The study was conducted in 21 Ontario urban/suburban communities ranging in population from 16,000 to 750,000. The study communities

RESULTS

Table 1 shows the characteristics of the 5,335 cardiac arrest cases from the study communities during phase I (July 1, 1991–January 31, 1995).

. Characteristics of study patients.

CharacteristicsPatients (n=5,335)*
Mean age (y; SD)68 (13.9)
Range16–102
Male sex (%)3,610 (67.7)
Community population size (%)
<30,000 (n=5)293 (5.5)
30,000 to 100,000 (n=5)1,141 (21.4)
100,000 to 200,000 (n=6)963 (18.1)
200,000 to 500,000 (n=4)1,970 (36.9)
>500,000 (n=1)968 (18.1)
Winter season (%)1,467 (27.5)
Witnessed arrest (%)

DISCUSSION

The OPALS Study represents the largest multicenter BLS-D study of prehospital cardiac arrest yet conducted. Our data clearly show that improved survival is associated with younger age and a witnessed event. Neither of these factors, however, can be improved on or optimized in an EMS system. We found 3 other independent factors associated with improved survival that are amenable to EMS system optimization. Survival may be enhanced by minimizing EMS response intervals, particularly the “call

Acknowledgements

We thank the OPALS Study Group investigators from the following base hospital programs: Burlington—Matthew W Stempian, MD, CCFP (EM), and Rose-Ellen G Rollins, RN; Cambridge—David Waldbillig, MD, CCFP (EM), Donald J Stewart, MD, MCFP (EM), and Bruce D Jermyn, RN, BScN, MBA; Kingston—Gordon J Jones, MD, FRCPC, Brian J Field, EMA III, and Thomas Bedford; London—Jonathan F Dreyer, MDCM, FRCPC, and Kenneth A Boyle, EMCA, EMT, RRT, CMA; Niagara—Douglas P Munkley, MD, MCFP (EM), and Lorraine G

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    Supported by grant 09194N from the Emergency Health Services Branch of the Ontario Ministry of Health, Ontario.

    ☆☆

    Dr Stiell is a career scientist of the Medical Research Council of Canada.

    Address for reprints: Ian G Stiell, MD, MSc, FRCPC, Clinical Epidemiology Unit, Ottawa Hospital Loeb Research Institute, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9; 613-798-5555 ext 8688, fax 613-761-5351.

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