Emergency medical services/original research
Effect of Transport Interval on Out-of-Hospital Cardiac Arrest Survival in the OPALS Study: Implications for Triaging Patients to Specialized Cardiac Arrest Centers

Presented at the 38th annual scientific meeting of the Society for Academic Emergency Medicine, May 2008, Washington, DC.
https://doi.org/10.1016/j.annemergmed.2008.11.020Get rights and content

Study objective

To identify any association between out-of-hospital transport interval and survival to hospital discharge in victims of out-of-hospital cardiac arrest.

Methods

Data from the Ontario Prehospital Advanced Life Support Study (January 1, 1991, to December 31, 2002), an Utstein-compliant registry of out-of-hospital cardiac arrest patients from 21 communities, were analyzed. Logistic regression identified factors that were independently associated with survival in consecutive adult, nontraumatic, out-of-hospital cardiac arrest patients and in the subgroup with return of spontaneous circulation.

Results

A total of 18,987 patients met criteria and 15,559 (81.9%) had complete data for analysis (study group). Return of spontaneous circulation was achieved in 2,299 patients (14.8%), and 689 (4.4%) survived to hospital discharge. Median transport interval was 4.0 minutes (25th quartile 3.0 minutes; 75th quartile 6.2 minutes) for survivors and 4.2 minutes (25th quartile 3.0, 75th quartile 6.2) for nonsurvivors. Logistic regression revealed multiple factors that were independently associated with survival: witnessed arrest (odds ratio 2.61; 95% confidence interval [CI] 2.05 to 3.34), bystander cardiopulmonary resuscitation (odds ratio 2.22; 95% CI 1.82 to 2.70), initial rhythm of ventricular fibrillation/tachycardia (odds ratio 2.22; 95% CI 1.97 to 2.50), and shorter emergency medical services (EMS) response interval (odds ratio 1.26; 95% CI 1.20 to 1.33). There was no association between transport interval and survival in either the study group (odds ratio 1.01; 95% CI 0.99 to 1.05) or the return of spontaneous circulation subgroup (odds ratio 1.04; 95% CI 0.99, 1.08).

Conclusion

In a large out-of-hospital cardiac arrest study from demographically diverse EMS systems, longer transport interval was not associated with decreased survival. Given the growing evidence showing major influence from specialized postarrest care, these findings support conducting clinical trials that assess the effectiveness and safety of bypassing local hospitals to take patients to regional cardiac arrest centers.

Introduction

Despite more than 4 decades of development of sophisticated emergency medical services (EMS) systems, very little is known about the effect of out-of-hospital care on patient outcomes.1, 2, 3, 4, 5 The most dramatic exception to this is the ability to successfully resuscitate victims of sudden cardiac death with timely provision of resuscitative care in the field.6, 7, 8, 9, 10 In fact, survival from out-of-hospital cardiac arrest is so extremely time-sensitive that, if patients do not achieve return of spontaneous circulation before arrival at the hospital, survival is exceptionally rare.11 Survival from out-of-hospital cardiac arrest is so dependent on timeliness and sequencing of specific interventions that, for decades, events occurring in the field were believed to be the only significant determinants of outcome.11, 12, 13, 14, 15, 16, 17 Perhaps this explains why a widespread sense of futility has been identified in the inhospital approach to patients who have return of spontaneous circulation but do not immediately appear to be neurologically and hemodynamically intact. Many patients with return of spontaneous circulation do not receive aggressive postarrest care after arrival at the hospital unless they are alert and relatively stable.18, 19, 20, 21, 22 However, this approach is highly inappropriate, given the results of several recent investigations. In the setting of aggressive postarrest critical care, the initiation of mild therapeutic hypothermia in patients who remained comatose after return of spontaneous circulation has yielded dramatic improvement in the rates of neurologically intact survival.23, 24, 25, 26, 27 With the appearance of hope that such care may have a major effect on outcome for patients with return of spontaneous circulation, the concept of bypassing closer hospitals en route to regional centers that can provide the entire spectrum of interventions and critical care has been suggested.28, 29 However, the potential benefits of triaging patients to more distant regional centers must be weighed against the risks involved in prolonging the time patients spend in the ambulance before arrival at the hospital.

Despite many years of intense investigation of out-of-hospital cardiac arrest, almost nothing is known about whether the amount of time required to transport the patient from the scene to the hospital affects patient outcomes. Without such information, the advisability of triaging patients to regional centers must be questioned. Thus, the objective of this study was to evaluate any potential effect of out-of-hospital transport interval on outcome, using patient data from a very large out-of-hospital cardiac arrest database.

Section snippets

Setting and Selection of Participants

The Ontario Prehospital ALS (OPALS) Study is a multicenter, multisystem, clinical trial evaluating numerous aspects of the effect of providing basic life support (BLS) and advanced life support (ALS) out-of-hospital care to patients presenting with out-of-hospital cardiac arrest. The methodology of the study has been reported in detail.30 The OPALS study was funded by Ontario Ministry of Health and Canadian Health Services Research Foundation.

Methods of Measurement

The cardiac arrest database developed for the study

Characteristics of Study Subjects

The Figure shows the adult out-of-hospital cardiac arrest cases of presumed cardiac origin that were entered into the OPALS database during the study period. Among the 20,695 cases, 1,708 were excluded because they were witnessed by EMS personnel, leaving 18,987 cases eligible for this analysis. Among these patients, 15,559 (81.9%) had complete data, and this cohort composed the overall study group. Patient outcome (the dependent variable) was missing in only 5 cases (0.024%). In the study

Limitations

This investigation has several limitations. First, this was a secondary review. Thus, unidentified confounders may have “masked” an underlying association between transport interval and survival. Despite this, we believe that the size of the database and the fact that the cases were prospectively entered into the study with the intention of specifically identifying the characteristics that affect survival add credence to the findings. Certainly the opposite finding would have been significant.

Discussion

A long history of intense evaluation has shown dramatic variation in the ability of EMS systems to affect survival from out-of-hospital cardiac arrest. In fact, success rates have varied across more than an order of magnitude: from dismal to impressive.6, 7, 8, 35, 36, 37, 38, 39 Until recently, emphasis on the out-of-hospital aspects of post–cardiac arrest care overshadowed discussions about the interventions and critical care provided after arrival at the hospital. This was partially due to

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    Supervising editor: Donald M. Yealy, MD.

    Author contributions: DWS, IGS, JM, JD, and GAW conceived the OPALS study, designed the original trial, obtained research funding, and supervised the conduct of the trial and data collection. All authors made substantial contributions to the conception and design of this secondary analysis and analyzed the meaning, conclusions, and limitations of the results. MDB and GAW provided statistical advice, and MDB analyzed the data and served as the statistical consultant. DWS drafted the article, and all authors contributed substantially to its revision. DWS 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. Funded by Ontario Ministry of Health and Canadian Health Services Research Foundation.

    Publication date: Available online January 23, 2009.

    Reprints not available from the authors.

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