Discussion

In view of the previous studies, the impact of DA-BCPR on survival and neurological outcomes with OHCA may be inconsistent. This systemic review and meta-analysis found DA-BCPR enhanced the provision of BCPR and improved the survival and neurological outcomes in pediatric and adult OHCAs. Survival to hospital admissions have shown trends of improvement but have yet to achieve statistical significance. European Resuscitation Council Guidelines for Resuscitation noted that dispatchers should provide telephone-CPR instructions in all cases of suspected CA, unless a trained provider is already delivering CPR.^{Reference Perkins, Olasveengen and Maconochie29}

Early detection, call for help, early access to emergency services, and promptly initiated CPR were very important and known as elements of the “chains of survival.”^{Reference Perkins, Olasveengen and Maconochie29-Reference Nakahara, Tomio and Ichikawa32} Previous studies showed that the survival rate decreased as CPR was delayed.^{Reference Larsen, Eisenberg, Cummins and Hallstrom33} Speedy BCPR is a key factor in improving survival from OHCA, offering a potential 50% decrease in mortality.^{Reference Herlitz, Bang and Gunnarsson34} Fifty-three percent of CAs were witnessed by a bystander; however, only 32% of victims actually received BCPR before arrival of EMS.^{Reference Sasson, Rogers, Dahl and Kellermann35} Because most OHCA events were witnessed, efforts to improve survival should focus on prompt delivery of interventions of known effectiveness by bystanders. This research demonstrated that DA-BCPR could improve the probability of BCPR. As the effectiveness of BCPR is time-dependent, DA-BCPR before EMS arrival should be encouraged. Though, 56% of CA patients in included studies still did not receive BCPR. Recognition of CA and prompt activation time on the part of emergency medical dispatch are key measures that have been associated with improved survival rates after OHCA.^{Reference Lewis, Stubbs and Eisenberg36}. Vaillancourt, et al found that dispatchers had 65.9% sensitivity and 32.3% specificity for the recognition of OHCA.^{Reference Vaillancourt, Charette and Kasaboski37} An optimized protocol, which includes a dispatcher education and training program, monthly debriefing meetings, and continuous quality control, is promising as it improved the successful recognition of CA.^{Reference Huang, Fan and Chien13} The sensitivity of medical priority dispatch systems in detecting CA was 76.7% and the specificity was 99.2%.^{Reference Flynn, Archer, Morgans and Morgans38} A longer detection time interval from the call for ambulance to the detection of OHCA by the dispatcher in DA-BCPR showed significantly lower good neurological recovery in adult patients with witnessed OHCA. A 30 second delay in detection time interval was associated with a three percent decrease of a good CPC score.^{Reference Ko, Shin and Ro39} Given this situation, simplified DA-BCPR instructions have resulted in time reduction and greater compression depth, even though the hand position might be corrected frequently in the conventional instruction group.^{Reference Dias, Brown and Saini40} Delays in the delivery of dispatcher-assisted CPR chest compressions are common and are attributable to a mixture of dispatcher behavior and factors beyond the control of the dispatcher.^{Reference Lewis, Stubbs and Eisenberg41} Inability to move patients to a hard, flat surface is associated with a reduced rate of DA-BCPR and increased time to first compression.^{Reference Langlais, Panczyk and Sutter42} Even trained bystanders sometimes hesitate to start CPR and the dispatcher can also in these cases play an important role.^{Reference Swor, Khan and Domeier43} Some standardized protocols have the potential to help bystanders initiate CPR.^{Reference Stipulante, Tubes and El Fassi44} Instruction on chest-compression-only CPR; education on how to recognize OHCA with agonal breathing, emesis, and convulsion; recommendations for on-line or re-dialing instructions; and feedback from emergency physicians increased the incidence of telephone CPR and BCPR, and also decreased the incidence of failed DA-BCPR.^{Reference Tanaka, Taniguchi and Wato12} On-going training of medical dispatchers to ensure recognition of OHCA during emergency calls and provision of DA-BCPR instructions to the bystander was encouraged in the 2015 European Resuscitation Council Guidelines as a strategy for improving OHCA recognition and performance of high-quality BCPR.^{Reference Greif, Lockey and Conaghan45}

As was shown in this study, DA-BCPR was able to improve the probability of ROSC before hospital admission and discharge or 30-day survival, as well as the neurological outcomes. The CPR performed before EMS arrival was associated with a 30-day survival rate after an OHCA that was more than twice as high as that associated with no CPR before EMS arrival.^{Reference Hasselqvist-Ax, Riva and Herlitz46} The quality of CPR and prolonged time interval from collapse to CPR have been suggested as possible causes for the limited survival effect of DA-BCPR, but the cause has not been determined.^{Reference Bohm, Vaillancourt and Charette10,Reference Harjanto, Na and Hao47,Reference Rea, Eisenberg, Culley and Becker48} Although a shorter delay from collapse to CPR,^{Reference Group17} the initiation of BCPR prior to the emergency call was not associated with an increase of ROSC or 30-day survival compared with DA-BCPR.^{Reference Viereck, Palsgaard Moller and Kjaer Ersboll49} Conventional CPR is a complex behavior; skill acquisition is difficult and skill retention has been shown to deteriorate rapidly with time following community resuscitation training programs for the lay public.^{Reference Chamberlain, Smith and Colquhoun50,Reference Madden51} Thus, DA-BCPR was originally intended to initiate CPR by bystanders with little or no training, but may be equally important for the large group of trained who panic and failed to start CPR.^{Reference Swor, Khan and Domeier43} Simulation studies suggest that bystanders without former CPR training who receive dispatcher-assisted instructions show comparable CPR skills to previously trained persons, although more time elapses before initiation of CPR for the untrained group.^{Reference Kellermann, Hackman and Somes52} The pre-arrival CPR instructions have been shown to increase the rate and depth of chest compression and improve the quality of BCPR, even in laypersons with previous CPR training.^{Reference Merchant, Abella and Abotsi53} It has been established that dispatcher assistance improves BCPR rates,^{Reference Bohm, Vaillancourt and Charette10,Reference Harjanto, Na and Hao47} which leads to better outcomes.^{Reference Wissenberg, Lippert and Folke54} Implementation of a standardized DA-BCPR protocol (such as medical priority dispatch and criteria-based dispatch) resulted in faster identification of CA, response team dispatching, and arrival at scene. These factors were associated with a trend to better survival.^{Reference Plodr, Truhlar and Krencikova55} Some measures were taken to improve the efficiency of DA-BCPR. Real-time smart-phone video conferencing calls between EMS personnel and physicians is feasible for patients with OHCA, and effective to improve the survival rate and cerebral function recovery rate.^{Reference Lee and Park56} A feedback CPR program with professional recording and feedback of CPR process was associated with good neurological recovery and survival to discharge.^{Reference Park, Shin and Ro57}