In addition to the factors of the instructor and the guide, the modes of communication, including telephone voice guidance and remote video online guidance, are important factors affecting the quality of DA-CPR. There is no unified quality evaluation standard for DA-CPR at home and abroad, but in the comprehensive literature(31, 32), the overall quality evaluation index recommends the time of dispatcher accepts emergency calls to judge suspected OHCA, time of starting guidance CPR, time of starting chest compressions, location of chest compressions, frequency and depth, etc. The AHA 2015 guidelines recommended high-quality CPR required adequate chest compression depth (50–60 mm), adequate chest compression rate (100–120/min), full chest wall recoil, minimal pauses in chest compressions, correct hand position during compressions, and avoidance of hyperventilation(10).
Our systematic review included 6 randomized controlled trials reporting on the quality of DA-CPR under different communication methods. The meta-analysis results showed that video communication could improve the average chest compression rate of bystanders during simulated CAs. The compression speed increased from an average of 92 min− 1 in the telephone group to more than 100 min− 1, reaching the standard compression rate for CPR. Abella et al. (22) found that a high chest compression rate is significantly related to the initial return of spontaneous circulation. It is expected that the compression speed improved by video communication can be transformed into a better chance of survival in reality. If the chest compressions are guided by moving video, it will be easier to maintain a proper chest compression rate. However, we also found, judging from the number of subjects who performed an adequate compression rate, there is still 10 ~ 70% proportion of subjects who did not achieve adequate compression rate. This reminds us that when guiding bystanders to perform cardiopulmonary resuscitation, we must emphasize that the compression frequency of bystanders reaches 100–120 times/min recommended by the AHA guidelines.
The depth of chest compressions is another key factor in high-quality CPR. Our meta-analysis revealed that video communication did not improve the average chest compression depth of bystanders during simulated CAs. At the same time, most of the compression depths did not meet the 2015 AHA guidelines for high-quality CPR with a depth of at least 5–6 cm in adults. Regardless of T-CPR or V-CPR, it is realized through interactive real-time feedback between dispatchers and subjects. In this study, most CPR performances did not meet the recommended compression depth. Therefore, it is necessary to emphasize the depth of chest compressions during interactive counseling, either through video presentations or phone calls.
Regarding the correct hand position during chest compressions, different description methods resulted in different results. When as a continuous variable, four studies indicated there was no significant difference between the V-CPR and T-CPR groups, but as the dichotomous variables, the other two studies showed V-CPR was significantly associated with the improved proportion of chest compressions with correct hand positioning. In included some studies, the correct hand position of the participants in T-CPR group was only 43.6%, and that of the participants in V-CPR group was only 45%. The possible reason is that the subjects in T-CPR group may call the dispatcher to ask questions, thus the position of their hands is changed during chest compressions. Video-guided CPR should be able to guide the correct hand position more intuitively in order to improve the correct hand position rate. However, some volunteers did not correct their hand position according to the instructions provided in the CPR video, which might be attributed to the small screen or location of the mobile phone. Different positions of the video phone may help to monitor and feedback the quality of CPR performed, such as the horizontal positioning, thereby achieving the adequate compression depth; on the other hand, the bird's eye view can optimize the judgment of hand positioning. Nevertheless, further research is needed to determine the best location of the video phone and the information obtained during DA-CPR.
Time to first chest compression is one of time-related quality parameters. In this meta-analysis, the V-CPR group had no significant improvement in time to first chest compression compared to the T-CPR group. In fact, only one study showed that the time to first chest compression was 72 s; while the remaining 5 studies were all greater than 100 s, and the longest reached 211 s. Such delay could have an impact on the survival rate of patients with CA. These were limited by the low quality of the video connection and poor training of the dispatcher in using video calls. Although the dispatcher gave accurate instructions, the bystanders in T-CPR group lacked a clear understanding and repeatedly asked questions, thus resulting in a time extension.
There were some inevitable limitations to this systematic review and meta-analysis. Firstly, this study incorporated simulation trials with mannequins, while might not represent real-life CAs. In fact, some bystanders can get plagued with fear; thus, more real-life studies with standardized protocols are needed in the future. Secondly, although the 2015 AHA guidelines recommended that dispatchers should provide CPR instructions with only chest compressions for adults with suspected OHCA, the emergency medical services are different and there are no unified standardized scheduling tools, hence, the instructions provided by the dispatcher may be varied. Thirdly, the research subjects included both adult volunteers and high school students, which could lead to differences in CPR quality due to their ability to learn from mobile videos. Although the adult volunteers (average age = 50 years) reported that they had no difficulty watching and understanding mobile videos, further research should be targeted on older volunteers who are more likely to encounter patients with CA. Fourthly, most included studies did not report the adjusted ORs of primary outcomes, and the ORs calculated by cross-tabs did not consider the confounding factors. Therefore, the results of this meta-analysis should be interpreted with caution.