Impact of dispatcher-assisted cardiopulmonary resuscitation on neurologically intact survival in out-of-hospital cardiac arrest: a systematic review

This systematic review was conducted according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines by three reviewers (KEE, GL, MTG) [29, 30]. The research question was developed on the PICOS framework recommended by the Cochrane Handbook [30, 31].

All studies with adult and/or pediatric OHCAs not witnessed by the Emergency Medical Services (EMS) that compared DA-CPR with bystander-initiated CPR and/or no bystander CPR before EMS arrival were included. DA-CPR was defined as OHCAs where bystanders provided CPR after instructions from the dispatcher. Bystander-initiated CPR was defined as OHCAs where bystanders initiated and provided CPR without assistance from the dispatcher. Studies only including traumatic OHCAs were excluded.

The primary outcome was neurologically intact survival at hospital discharge or at least one-month after OHCA. Neurologically intact survival was defined as Cerebral Performance Category (CPC) 1 or 2 or modified Rankin Scale (mRS) 0–3. CPC level 1 represents “good recovery”, and CPC 2 means “moderate disability / disabled but independent” [32, 33].

Secondary outcomes were survival to hospital discharge, or at least one-month survival, and prehospital ROSC or ROSC at hospital arrival.

Only studies written in English were eligible. Simulation studies, case reports, and conference abstracts were excluded. No restrictions on publication and study years were applied.

The following databases were systematically searched: PubMed (MEDLINE), EMBASE, and the Cochrane Library. In collaboration with a professional librarian from Copenhagen University Library, the search was designed to include all studies covering both cardiopulmonary resuscitation and dispatcher assistance. Table 1 provides the search string designed for the PubMed (MEDLINE) database. The search was modified to fit EMBASE and the Cochrane Library databases. The search was performed on the April 14th 2020 in all three databases.

First, two independent reviewers screened all titles and abstracts for eligibility (KEE and GL/MTG). If any disagreement the full-text article was screened. The same reviewers independently screened the selected full-text articles. Any disagreement was resolved by discussion until consensus. Finally, the reference lists of all eligible studies were screened by the first reviewer (KEE) for studies that fulfilled the inclusion criteria [34].

Publications with overlapping study populations were considered duplicates, and only one was included in the final review. The study that reported the primary outcome, neurologically intact survival, was selected for inclusion. If equally relevant, the decision was based on whether secondary outcomes were reported, and finally, the study analyzing the effect of DA-CPR on the largest population was selected.

Outcomes were also assessed for the subgroup of studies including only witnessed arrests. Among the list of eligible studies according to PICOS, studies with witnessed arrests only were extracted, subsequently the criteria for removing publications with overlapping study populations were applied.

Data were extracted into predefined tables by the first reviewer (KEE) and confirmed by a second reviewer (GL/MTG). Data on study characteristics included: study design, inclusion and exclusion criteria, period, country of origin, data sources, and the existence of a standardized CPR instruction protocol and type of basic life support (BLS) instructed (e.g. compression only). Patient data included: age and sex of victim, witnessed status, etiology of arrest, the initial cardiac rhythm, and location of arrest, along with the total number of OHCA analyzed with/without DA-CPR. Finally, outcome measures extracted included: neurologically intact survival and survival at discharge and one-month or longer, and ROSC.

Risk of bias was assessed using the Newcastle-Ottawa Scale by two reviewers (KEE and GL/MTG) [35]. The Newcastle-Ottawa Scale is developed to assess the quality of non-randomized studies by rating three domains of case-control and cohort studies: 1) Selection of study groups, 2) comparability of groups, and 3) ascertainment of exposure or outcome. A study can be awarded from zero to nine stars; nine stars representing a low risk of bias. In the comparability domain, this review defined the most important factor as “witnessed arrest”, according to the findings by Sasson et al. 2010 [36]. A study was awarded one star for comparability if it controlled for “witnessed arrest”, either by study design in the inclusion/exclusion criteria, or in the analyses e.g. by conducting a logistic regression. An additional star was awarded if the study controlled for an additional factor. If less than 10% of the OHCAs were excluded from the analyses because of missing data, one star was awarded for adequacy of follow-up in the outcome domain.

Median and interquartile range (IQR) for the primary and secondary outcome measures were calculated. For neurologically intact survival, unadjusted odds ratios and confidence intervals comparing DA-CPR and bystander-initiated CPR with no bystander were determined.

The included studies were awarded from 6 to 9 stars on the Newcastle-Ottawa Scale (Table 2). The most common reason for increased risk of bias according to the Newcastle-Ottawa Scale (lower score) was that the study did not control for confounding factors.

Results of individual studies are presented in Tables 3, 4, and 5 and in Fig. 2, which show that generally, the higher odds for neurologically intact survival with bystander-initiated CPR without dispatcher assistance compared with DA-CPR were reduced when adjusting for confounding factors.

Median neurologically intact survival at discharge with DA-CPR was 7.0% (IQR: 5.1–10.8%), with bystander-initiated CPR without dispatcher assistance 7.5% (IQR: 6.6–10.2%), and with no provision of bystander CPR before EMS arrival 4.4% (IQR: 2.0–9.0%) (four studies, Fig. 3, Table 3) [37, 42, 44, 47]. At one-month, median neurologically intact survival was 3.1% (IQR: 1.6–3.4%) with DA-CPR, 5.7% (IQR: 5.0–6.0%) with bystander-initated CPR, and 2.5% (IQR: 2.1–2.6%) with no bystander CPR (three studies, Fig. 3, Table 3) [38, 39, 45]. Only one study reported neurologically intact survival at longer follow-up (six-months) [40].

When excluding studies with only pediatric patients (2 studies), median neurologically intact survival at discharge with DA-CPR was 8.8% (IQR: 6.9–12.8%), with bystander-initiated CPR without dispatcher assistance 9.3% (IQR: 7.5–11.1%), and with no bystander CPR 6.6% (IQR: 4.4–11.3%) [42, 44, 47]. At one-month, the numbers were 1.6% (IQR: 0.8–2.3%) for DA-CPR, 5.0% (IQR: 4.6–5.3%) with bystander-initiated CPR, and 2.1% (IQR: 1.9–2.4%) with no bystander CPR [39, 45].

Eleven out of the 33 eligible studies met the additional criteria of witnessed OHCA. Of these 11 studies, three did not provide data on neurologically intact survival, and after removing studies with overlapping study populations four studies remained (Table 2 and Supplementary Material Table 1). Lee et al. [49] reported neurologically intact survival to discharge; DA-CPR: 8.8%; bystander-initiated CPR 10.1%; no bystander CPR 4.2%. Shimamoto et al. [50] and Takei et al. [26] reported neurologically intact survival at one-month; DA-CPR: 6.0% & 4.5%; bystander-initiated CPR: 8.3% & 6.0%; no bystander CPR: 3.4% & 3.1%. Hiltunen et al. [40] reported for a 6-months follow-up (Table 3).

For the secondary outcomes, median ROSC was 16.0% (IQR: 8.3–30.4%) in the DA-CPR group, 20.9% (IQR: 11.8–35.8%) in the bystander-initiated CPR group, and 11.6% (IQR: 4.9–24.2%) in the no bystander CPR group (seven studies, Table 4) [37, 39, 40, 44‐47].

Median survival to hospital discharge with DA-CPR was 15.2% (IQR: 8.6–20.7%), with bystander-initiated CPR survival was 15.5% (IQR: 14.2–23.1%), and with no bystander CPR 10.0% (IQR: 4.7–14.3%) (nine studies, Fig. 4, Table 5) [17, 25, 37, 40‐44, 47]. At one-month median survival rate was 10.9% (IQR: 5.6–11.5%) with DA-CPR, 14.9% (IQR: 8.7–15.4%) with bystander-initated CPR, and 5.0% (IQR: 4.1–6.7%) with no bystander CPR (five studies, Fig. 4, Table 5) [7, 38, 39, 45, 46].

This systematic review suggests that DA-CPR increases the rate of neurologically intact survival compared with no bystander CPR. Odds ratios adjusted for established confounders that compared DA-CPR with no bystander CPR are provided by five studies. They all report significantly higher odds of neurologically intact survival with DA-CPR [37, 38, 44, 45, 47].

Previous studies demonstrate the effect of immediate bystander CPR, which slows the inevitable decline in survival until defibrillation and advanced EMS treatment [5, 51]. The studies included in this review show an increase in ROSC with DA-CPR compared with no bystander CPR. Thus, the prehospital intervention is strengthened by the dispatchers and their role in motivating and assisting bystanders to provide early CPR. Also, survival rates are higher with DA-CPR than no bystander CPR for all follow-up periods reported.

DA-CPR appears inferior to bystander-initiated CPR without dispatcher assistance looking at the crude neurologically intact survival outcomes, as well as ROSC and survival. However, when adjusting for confounding factors the difference is reduced, and confounding factors account for some of the difference in the crude neurologically intact survival outcomes between the DA-CPR group and bystander-initiated CPR group. For example, witnessed arrest and initial-shockable rhythm, two established predictors of survival, are both seen more frequently in the bystander-initiated CPR group than in the DA-CPR group [36]. It is likely that time to first compression is shorter for bystander-initiated CPR, because a trained bystander can recognize and initiate CPR without the delay of the emergency call, during which the dispatcher first has to recognize cardiac arrest and secondly provide instructions on CPR [46]. A trained bystander initiating CPR reduces time to first compression and increases time with CPR until EMS arrival compared with an untrained bystander relying on dispatcher assistance; time factors that are associated with higher survival rates [7, 24‐26].

Simulation studies have demonstrated comparable quality of DA-CPR and bystander CPR without dispatcher assistance [27, 28]. Whether the results are transferable to real-life OHCA resuscitation attempts has not yet been proven, and differences in CPR quality may account for differences in outcomes. Finally, most of the simulation studies have investigated the quality of CPR among young adults while the majority of cardiac arrests occur in men above 60 at home [13]. This leaves CPR to his elderly wife, and physical limitation is a frequent reason for bystanders to reject CPR [52].

Little consensus exists on how to define and report DA-CPR [33, 53]. This means that variability in extent and quality of dispatcher instructions, and the extent and quality of the bystanders’ CPR attempt will influence OHCA outcomes and may produce inter-study variability. For example, none of the included studies specified what motivation and instruction the dispatcher needed to provide in order to define the bystander attempt as dispatcher-assisted. Also, information defining the actions bystanders were to provide and how the provision of bystander CPR was determined varied and sometimes lacked. In some studies bystander CPR was determined from the emergency call, while in other studies from the report of on-site EMS personnel. Both methods have limitations, i.e. Linderoth et al. [54] found that the understanding of bystander interventions from emergency call records was not always accurate (assessed emergency call records versus closed-circuit televisions from public locations).

The outcomes in OHCAs with dispatcher assistance reported in this review reflect cases where the bystander initiated CPR following instructions. Not every attempt by the dispatcher results in bystander CPR, which is further discussed in Supplementary Material 2.

This review focuses on neurologically intact survival, a marker for not only survival but survival with preserved neurologic function and quality of life. A systematic, recent and comprehensive literature search was performed using broad search criteria to report contemporary knowledge and minimize selection bias. Study characteristics and results of individual studies are presented along with any study-reported adjusted outcomes for transparency incl. transparency of the inter-study variability. Summary measures are provided to condense contemporary knowledge.

In future studies, it may be relevant to assess the effect of DA-CPR in untrained vs. trained bystanders as training status may confound the results of the current publications. Also, the DA-CPR protocol should likely be adjusted to the training status of the bystanders and the setting and situation of the OHCA, why a “one-size-fits-all” protocol may not exist. New technological solutions such as live video streaming from the OHCA location transmitted via the bystander’s smartphone to the dispatcher may enhance communication and improve the quality of the DA-CPR.