Tipos de estudios

Se incluyeron ensayos aleatorios y cuasialeatorios (ECA y ECCA) que comparaban la atención habitual de los servicios médicos de urgencia (SMU) versus la atención de los SMU más la movilización de los primeros intervinientes de la comunidad (PSC) en los casos de paro cardíaco extrahospitalario (PCEH). Los ensayos con asignación al azar por grupos fueron elegibles para la inclusión, incluidos los estudios de diseño grupal con cruzamiento (cross‐over) de la intervención.

Un ensayo se consideró elegible cuando, sobre la base de la mejor información disponible, se consideraba que los participantes seguidos en el ensayo habían sido asignados de forma prospectiva a la atención habitual de los SMU o a la atención habitual de los SMU con el agregado de la movilización de los PSC, mediante un método de asignación aleatorio o cuasialeatorio (Higgins 2011).

La movilización de los PSC a la escena del PCEH representa una intervención comunitaria compleja que puede depender de estructuras organizacionales fuera del control del sistema de salud. Es probable que en algunos casos no sea factible que los diseños de los ensayos utilicen la asignación aleatoria con participantes individuales que representen la unidad de asignación. Por esta razón, se consideraron elegibles para la inclusión en esta revisión los ensayos aleatorios y cuasialeatorios que incluían métodos grupales.

Se excluyeron los estudios que consideraban principalmente el PCEH debido a causas traumáticas, debido a que es poco probable que las intervenciones centrales proporcionadas por los PSC, a saber, la reanimación cardiopulmonar (RCP) y la desfibrilación precoz, tengan un beneficio significativo en dichas circunstancias.

Tipos de participantes

Se incluyó a adultos y niños mayores de cuatro semanas de vida que habían padecido un PCEH.

Se excluyeron los estudios que consideraban principalmente el PCEH en neonatos al nacer.

Tipos de intervenciones

Se incluyeron estudios que comparaban la atención de rutina de los SMU (grupo de control) versus la atención de los SMU más la movilización de los PSC (grupo de intervención) en los casos de PCEH.

Los primeros intervinientes de la comunidad se definieron según la sección Descripción de la intervención (más arriba). Los primeros intervinientes de la comunidad fueron individuos dentro de una comunidad que estaban organizados en un marco que ofrecía atención del PCEH dentro de dicha comunidad para complementar la respuesta estándar de los SMU.

La movilización de los PSC a la escena de un evento de PCEH representó una intervención compleja con variación en los componentes dependiendo del ámbito de la comunidad y su sistema de prestación de atención médica de emergencia. Entre las características clave que definieron a los PSC en diferentes entornos y sistemas de atención se incluyen las siguientes.

• Los intervinientes de la comunidad estuvieron presentes en la comunidad donde ocurrió el paro cardíaco.

• Los intervinientes de la comunidad no tenían la responsabilidad reglamentaria de la respuesta a un paro cardíaco, sino que más bien servían para complementar la respuesta reglamentaria de los SMU.

• Los primeros intervinientes de la comunidad fueron movilizados a un evento de PCEH por un mecanismo de alerta activo y predeterminado.

En algunas comunidades, el SMU reglamentario o el servicio de ambulancia es proporcionado de forma sistemática por el servicio de bomberos local. Con objeto de realizar esta revisión, este grupo representa el SMU reglamentario, como diferenciado de los PSC, y no se incluyó como una intervención elegible.

No se incluyeron los estudios centrados principalmente en los espectadores casuales. Los individuos que estuvieron presentes en el lugar de un evento de PCEH y que realizaron RCP de acuerdo con la instrucción telefónica proporcionada por quienes tomaron la llamada del SMU no se consideraron PSC.

También se excluyeron los estudios que evaluaban principalmente la repercusión de intervenciones adicionales específicas como la administración de naloxona en la sobredosis de narcóticos o de adrenalina en la anafilaxia.

Tipos de medida de resultado

Búsquedas electrónicas

We identified RCTs and q‐RCTs through literature searching designed to identify relevant trials, as outlined in Chapter 6.4 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). We did not apply restrictions by language or publication status.

We searched the following databases for relevant trials.

• Cochrane Central Register of Controlled Trials (CENTRAL), in the Cochrane Library, on 16 February 2018.

• MEDLINE (Ovid SP, 1946 onwards), on 16 February 2018.

• Embase (Ovid SP, 1974 onwards), on 19 February 2018.

• Web of Science (1960 to present), on 16 February 2018.

We listed the search strategies used for each database in Appendix 1. We updated the search strategy in January 2019 and re‐ran the searches. We screened all new references obtained but detected no additional eligible studies.

We scanned the following trials registries on 20 August 2018 for ongoing and unpublished trials.

• World Health Organization International Clinical Trials Registry Platform (www.who.int/ictrp/en/).

• ClinicalTrials.gov.

Búsqueda de otros recursos

We scanned the reference lists and citations of included trials for further references to additional trials. We also scanned the abstracts of conference proceedings of the American Heart Association and the European Resuscitation Council. When necessary, we contacted trial authors to request additional information.

Selección de los estudios

Two review authors (TB and MD) independently reviewed all titles and abstracts received to assess potential eligibility, using the inclusion criteria outlined above. We obtained and examined in detail full‐text copies of all papers considered potentially eligible, and we approached authors of trials for additional information when necessary. We resolved disagreements by discussion, and when necessary, we involved a third review author (GB or RS). We have summarized the process of study selection in a PRISMA flowchart (Moher 2009).

Extracción y manejo de los datos

Three review authors (TB, GB, and MD) independently extracted relevant data using our standard data extraction form (Appendix 2), which we adapted from the version used by the Cochrane Effective Practice and Organisation of Care Group (EPOC 2013).

We collected information on study design, study setting, participant characteristics, eligibility criteria, details of intervention(s) given, outcomes assessed, sources of study funding, and any conflicts of interest. We contacted authors of included trials to request additional information when this was necessary. We resolved any disagreements by discussion and consensus.

Evaluación del riesgo de sesgo de los estudios incluidos

Three review authors (TB, GB, and MD) independently assessed the validity of each included trial using the Cochrane 'Risk of bias' tool and provided a summary assessment of risks of bias across studies (Higgins 2011).

We assessed each included trial according to the following domains: sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective outcome reporting, and other potential sources of bias. Where relevant, the latter included sources related to a cluster‐randomized design such as (1) recruitment bias; (2) baseline imbalance; (3) loss of clusters; (4) incorrect analysis; and (5) comparability with individually randomized trials, as outlined in Section 16.3.2 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). For the domain of 'incomplete outcome data', we assessed risk of bias at the outcome level rather than at the study level.

We considered low risk of bias to represent studies with plausible bias unlikely to seriously alter the results; unclear risk of bias to represent studies with plausible bias that raises doubts about the results; and high risk of bias to represent studies with plausible bias that seriously weakens confidence in the results (Higgins 2011). We resolved any disagreements by discussion and consensus.

We constructed a 'Risk of bias' table and generated plots of risk of bias assessments using Review Manager 5 (Review Manager 2014).

Medidas del efecto del tratamiento

We used odds ratios (ORs) with 95% confidence intervals (CIs) to measure the following dichotomous outcomes.

• Survival at hospital discharge.

• Survival at 30 days.

• Survival to hospital admission.

• Cardiopulmonary resuscitation performed before EMS arrival.

It was not possible to calculate an OR for 'defibrillation performed before ambulance service arrival', as in the only study that reported this outcome, no cases occurred in the control group.

We planned to group neurological outcomes into categories of favourable (CPC score of 1 or 2) and unfavourable (CPC score of 3, 4, or 5), as suggested in a previous systematic review concerning OHCA (Huang 2014); however, data for this outcome were not available.

Health‐related quality of life can be measured by many different tools, including the Quality of Life Scale, the Personal Wellbeing Index, Short Form‐36, and the Satisfaction With Life Survey (Dronavalli 2015), with potentially varying validity for this target population. We anticipated substantial heterogeneity in measuring this outcome, and for this reason, planned to assess treatment effects of health‐related quality of life by narrative description and tabulation in this Review. Unfortunately, outcome data for health‐related quality of life were not available.

Cuestiones relativas a la unidad de análisis

We planned that if we included studies with multiple treatment groups, we would follow the recommendations of Higgins 2011 and would combine groups to create a single pair‐wise comparison or would select one pair of groups and exclude the other groups. This was not necessary, as we included no such studies.

We included one cluster‐randomized trial and evaluated whether clustering was accounted for in the determination of required sample size, whether assessment for design effect was carried out, and whether methods used in analysis are appropriate to the cluster design. Had such a study been inappropriately analysed, as though randomization was performed by individual rather than by cluster, we would have adhered to the advice provided in the Cochrane Handbook for Systematic Reviews of Interventions, Section 16.3.4 (Higgins 2011), and we would have adjusted for design effect when possible. This would have necessitated a request to investigators for additional individual‐level data to allow assessment of the intraclass correlation coefficient (ICC) in clusters. As we judged the methods used in the analysis to be appropriate, we believed this was not necessary.

Manejo de los datos faltantes

When summary statistics were missing, we contacted the first author of the trial to try to retrieve relevant data in the first instance.

When individual studies did not account appropriately for missing data, or did not report how these were handled, we considered whether data were likely to be missing at random or otherwise, and we assessed the resulting risk of bias.

When outcome data were missing and could not be recovered, we adopted the approach suggested in the Cochrane Handbook for Systematic Reviews of Interventions, Section 16.2.1 (Higgins 2011), and we used available‐case analysis. We included data only for participants whose results were known, and we addressed the potential impact of the missing data by using the 'Risk of bias' tool. Ultimately, we considered the potential impact of including such studies in the overall assessment of intervention effect.

Evaluación de la heterogeneidad

We considered clinical heterogeneity, methodological heterogeneity, and statistical heterogeneity as outlined by Higgins 2011.

We addressed clinical heterogeneity through detailed reporting of the diagnostic and clinical definitions and characteristics of the included studies. We planned to conduct meta‐analysis if we considered the included studies to be sufficiently homogeneous for participants, interventions, and outcomes. However, the included studies were too heterogeneous for review authors to proceed.

We assessed methodological heterogeneity using the Cochrane 'Risk of bias' tool.

We planned to assess statistical heterogeneity by considering the consistency of study results, and by examining how this impacted the planned meta‐analysis. However as already stated, the included studies were too heterogeneous for review authors to proceed with meta‐analysis. Formerly, we had planned to use the Chi² test and to consider P < 0.10 to represent significant heterogeneity. We also had planned to use the I² statistic to describe the percentage of variability in effect estimates that is due to heterogeneity rather than to sampling error (chance), and to assess its potential impact on the planned meta‐analysis. We had planned to interpret the I² result in keeping with guidance provided in Section 9.5.2 of the Cochrane Handbookfor Systematic Reviews of Interventions (Higgins 2011).

Evaluación de los sesgos de notificación

We planned to create a funnel plot to explore publication bias if at least 10 studies were included in the meta‐analysis. However, we found too few studies and did not proceed with meta‐analysis for the reasons already outlined.

Síntesis de los datos

We planned to perform a meta‐analysis; however as already stated, the included studies were too heterogeneous for us to proceed.

We had planned to use a random‐effects meta‐analysis to provide some robustness against the presence of heterogeneity, with inverse variance weighting provided by the DerSimonian‐Laird estimate of between‐study variance (tau²) (DerSimonian 1986), and with all analyses carried out in Review Manager 5 (Review Manager 2014).

As we deemed individual study designs to be too diverse, and thus statistical combination to be inappropriate, we have presented the findings in a narrative fashion.

Análisis de subgrupos e investigación de la heterogeneidad

We planned a priori subgroup analysis for our primary outcomes in keeping with the following characteristics and rationale.

• Geographical setting (primarily urban or non‐urban): urban CFR mobilization may allow shorter response time.

• Cadre of CFRs (trained laypersons, police service, fire service, and off‐duty paramedics): this may influence CFR training, scope of the intervention, and response time.

• Community first responders routinely equipped with a defibrillator: defibrillation is a key time‐critical intervention after OHCA.

• Witnessed OHCAs: these are likely to have shorter intervals to initiation of CPR and defibrillation from time of OHCA.

• Age groups (children defined as individuals up to 15 years old vs adults): common causes of OHCA are different in children (Meyer 2012), and this may affect the efficacy of interventions.

However, we did not undertake pooled subgroup analysis because we found insufficient data.

Análisis de sensibilidad

We planned to perform sensitivity analysis by excluding studies considered to have high risk of bias; however, the heterogeneity of included studies and insufficient data precluded both meta‐analysis and sensitivity analysis.