Article Text
Abstract
Aim Untrained laypersons should perform compression-only cardiopulmonary resuscitation (COCPR) under a dispatcher's guidance, but the quality of the chest compressions may be suboptimal. We hypothesised that providing metronome sounds via a phone speaker may improve the quality of chest compressions during dispatcher-assisted COCPR (DA-COCPR).
Methods Untrained laypersons were allocated to either the metronome sound-guided group (MG), who performed DA-COCPR with metronome sounds (110 ticks/min), or the control group (CG), who performed conventional DA-COCPR. The participants of each group performed DA-COCPR for 4 min using a manikin with Skill-Reporter, and the data regarding chest compression quality were collected.
Results The data from 33 cases of DA-COCPR in the MG and 34 cases in the CG were compared. The MG showed a faster compression rate than the CG (111.9 vs 96.7/min; p=0.018). A significantly higher proportion of subjects in the MG performed the DA-COCPR with an accurate chest compression rate (100–120/min) compared with the subjects in the CG (32/33 (97.0%) vs 5/34 (14.7%); p<0.0001). The mean compression depth was not different between the MG and the CG (45.9 vs 46.8 mm; p=0.692). However, a higher proportion of subjects in the MG performed shallow compressions (compression depth <38 mm) compared with subjects in the CG (median % was 69.2 vs 15.7; p=0.035).
Conclusions Metronome sound guidance during DA-COCPR for the untrained bystanders improved the chest compression rates, but was associated more with shallow compressions than the conventional DA-COCPR in a manikin model.
- resuscitation
- prehospital care, despatch
- prehospital care, first responders
- first responders
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Introduction
Early bystander cardiopulmonary resuscitation (CPR) at the scene of a victim's arrest can increase the chance of survival after an out-of-hospital cardiac arrest (OHCA).1 – 4 All bystanders must activate the emergency medical services (EMS) system immediately and provide chest compressions upon recognition of a possible cardiac arrest victim.2 However, the first responders may have no experience or education in CPR, and therefore, an EMS dispatcher should give instructions to the caller for chest compression-only CPR (COCPR) until trained EMS rescuers arrives.2 Dispatcher-assisted CPR is a key link in the chain of survival, and this is an important EMS system for survival of an OHCA.4–10 This system can increase the chance that chest compressions will be performed by untrained laypersons, but the quality of the chest compressions may be suboptimal compared with the recommendations of the current guidelines.11–15
During CPR, real-time guidance with metronome sounds is an attractive feedback method to ensure the delivery of an accurate rate of chest compression.16–18 This device is simple, cheap and easily available in any environment. Many simulation trials and clinical setting studies have demonstrated improvement of CPR quality with use of audible guidance, such as a metronome or other audible prompt devices.16–21 Recent advances in the speaker function of telephones may provide a good opportunity for communication between the dispatcher and layperson while performing CPR.22
We hypothesised that if dispatchers play metronome sounds via a telephone speaker to the untrained laypersons during COCPR, higher-quality chest compressions can be delivered. To verify this hypothesis, we conducted a randomised controlled simulation study to compare the quality of chest compressions in dispatcher-assisted COCPR (DA-COCPR) with and without metronome guidance.
Methods
Study design and subjects
This study used and performed a randomised controlled trial design in the simulation setting using a manikin. First, the study protocol was reviewed and approved by a university's institutional review board, and written informed consent was obtained from each participant. This simulation trial was conducted at the Basic Life Support (BLS) training centre of the Gyeongsang-Namdo Emergency Medical Information Centre at the university teaching hospital in an urban area. From October 2011 to February 2012, participants were recruited from adult (age >18) laypersons who attended the BLS training courses provided by the BLS training centre of the Gyeongsang-Namdo Emergency Medical Information Centre. Among the participants, those who had no BLS training within the preceding 5 years, and no health problems inhibiting their ability to perform the chest compressions were recruited for the simulation trial. Referencing the data on CPR quality in prior simulation metronome studies,16–18 we assumed that 90% of the group with metronome guidance would have an appropriate compression rate, compared with 60% of the group without guidance. The SD was hypothesised to be 10% in both groups. For an α error of 5% (two-sided) and a power of 80% in the randomised controlled design between the two groups, we estimated that a minimum sample size of 29 would be required in each group. Considering a 20% exclusion rate, we aimed to recruit a total of 70 subjects (35 for each group).
Study procedure
We randomised the two trial groups by the sealed envelope selection method (35 sealed envelopes containing a paper labelled ‘the metronome group’ (MG), and 35 envelopes containing a paper labelled ‘the control group’ (CG)). The subjects selected one sealed envelope and then entered the simulation room. We were not informed to which group the participants were allocated.
Before the study, we briefly explained the overview of DA-COCPR to the subjects and introduced them to the simulation room. In the room, we prepared the Resusci Anne SkillReporter on the floor, which was connected to a laptop with the Laerdal PC Skill Reporting System programme (Laerdal Medical Corporation, Stavanger, Norway). The cellular phone (LG-SH860, LG Corporation, Seoul, Korea) was beside the manikin for DA-COCPR.
The simulation scenario consisted of a witness of an OHCA, the activation of the EMS system with the prepared cellular phone, and the performance of bystander COCPR according to the instructions of the dispatcher. After the participant entered the room alone, the participant checked the responsiveness of a manikin on the floor (awareness) and then phoned the dispatcher with the prepared cellular phone. An emergency physician who had ample experience providing medical directions to EMS workers played the role of the dispatcher. The dispatcher stayed outside the simulation room and was not able to see the performance of the participant inside the simulation room. The dispatcher communicated with the subjects only through the cellular phone.
Upon receiving a call from the participant inside the simulation room, the dispatcher instructed the layperson to provide the location and situation of the arrest accident and then encouraged the layperson to perform COCPR. Before beginning the COCPR, the dispatcher instructed the layperson to activate the speaker function of the cell phone and to lay it next to the manikin. Using the speaker function, audible guidance of COCPR was given to the rescuer. For the CG, conventional verbal guidance on high-quality chest compressions (location of hand placement, speed of >100 per min, depth of >50 mm and complete release)2 was provided, and verbal encouragement was given repeatedly throughout the COCPR. For the MG, after providing the same guidance on chest compression technique as the CG, metronome sounds (110 ticks/min; median value of 100–120 compressions/min)2 were played to the rescuer through the speaker during the COCPR instead of repeat verbal encouragement. To standardise the study procedure, the instruction scripts containing the conversation were given to the participants and dispatcher. We made these scripts by referencing the CPR guidelines and dispatcher guidance of Korean EMS system. The subjects performed 4 min of COCPR until the arrival of an ambulance was simulated.
Assessment and data analysis
The values assessing chest compression quality for 4 min of COCPR were obtained for each layperson from the recorded data of the Laerdal PC Skill Reporting System (Laerdal Medical Corporation, Stavanger, Norway). The primary outcomes were the rate of chest compressions (min) and the numbers of providers who performed at chest compressions with appropriate rate (100–120 compressions/min). Additionally, the data for compression depth (mean value, proportion of compression depth <38 mm and proportion of compression depth >50 mm),23 compression duty cycle, proportion of incomplete chest release, proportion of abnormal hand positions and total number of chest compression were analysed.
All the collected data were analysed using statistical software (SPSS V.17.0, SPSS, Inc, Seoul, Korea). To compare the normally distributed data (presented as mean and SD) between the MG and the CG, independent Student t tests were used. To compare the non-normally distributed data (presented as median and IQR), Mann–Whitney U tests were used. Two-sided p values less than 0.05 were considered statistically significant.
Results
Subjects
Of the 112 adult laypersons who participated in the BLS training course, 42 were excluded because of prior experience with BLS training (38), disagreeing with the trial (3) and a health problem (1). A total of 70 volunteers (35 in the MG and 35 in the CG) were finally enrolled in our trial. During the simulation trial, two subjects in the MG and one subject in the CG gave up the completion of 4 min of COCPR. The COCPR data for 33 subjects in the MG and 34 subjects in the CG were collected and analysed (figure 1). Baseline characteristics, including age, gender, body mass index, experience with CPR education within 5 years, and level of education (university graduate), were not significantly different between the groups (table 1).
Quality of chest compressions
The compression rate was faster in the MG than the CG (111.9 vs 96.7/min, respectively; p=0.018), and the MG delivered a higher number of chest compressions than the CG (439.3 vs 385.1/min, respectively, p=0.040) (table 2). A significantly larger number of subjects in the MG performed the COCPR with an appropriate chest compression rate (100–120/min) than the subjects of the CG (32/33 (97.0%) vs 5/34 (14.7%), respectively; p<0.0001). The CG showed a wider distribution outside of the appropriate compression rate than the MG (figure 2). No significant difference in the mean compression depth was shown between the MG and the CG (45.9 vs 46.8 mm, respectively; p=0.692). A higher proportion of compression depth <38 mm was shown in the MG than the CG (median % was 69.2 vs 15.7; p=0.035). For the compression duty cycle, the proportion of incomplete chest release and the proportion of abnormal hand positions, there were no significant differences between the two groups (table 2).
Discussion
This simulation study is the first to evaluate the efficacy of metronome guidance during DA-COCPR by an untrained layperson. The addition of metronome sounds could partially improve the quality of chest compressions (higher proportion of appropriate rate of chest compressions and higher number of chest compressions) during the 4 min of simulated DA-COCPR by untrained laypersons, when compared with conventional verbal instructions by a dispatcher. However, the metronome guidance was not associated with better compression depth, less incomplete release or more correct hand positions than the conventional verbally guided subjects.
DA-COCPR for an untrained rescuer
To improve the survival rate of adult OHCA victims, early bystander CPR should be performed after activation of the EMS.2–4 ,24 Many bystanders may lack experience or education in CPR and are not familiar with a situation as chaotic as cardiac arrest.3 ,24–26 To encourage and guide CPR performed by a lay bystander, DA-CPR systems have been established.5–7 This system could increase the performance of bystander CPR at the scene and improve the survival rate of OHCAs.8–10 ,27 Dispatcher-assisted CPR includes recognition of cardiac arrest, start of CPR and methods of CPR. Recent studies have shown that COCPR has beneficial effects on the survival of OHCAs, especially for witnessed cardiac arrests or cardiac arrests with a shockable rhythm.28 Whether COCPR achieves a better survival rate than the conventional 30 : 2 CPR is controversial,25 ,29–31 but COCPR is the best option for untrained rescuers because ‘mouth-to-mouth’ ventilation is too difficult and frightening for them.2 According to the 2010 guidelines, a dispatcher should immediately commend an untrained bystander to perform COCPR to the suspected arrest victim. COCPR with the DA-CPR system can increase the incidence of CPR by an untrained bystander, but this is usually commended by verbal instructions via the phone, and the quality of chest compression may not be monitored. The quality of COCPR guided only by the verbal instructions of the dispatcher may be suboptimal compared with the guideline recommendations. There are no known clinical data analysing the quality of CPR performed by an untrained bystander, but some simulation studies have shown insufficient quality chest compressions, especially in regard to chest compression rate.13–15 To overcome this problem, we should design a method to improve the quality of bystander COCPR with dispatcher assistance. Considering the brief communication time between the bystander and dispatcher until EMS arrival at the scene and the lack of training in CPR, a method for improving the quality of bystander COCPR with dispatcher assistance may be very difficult to establish. Recently, a simulation trial showed that the interactive video instruction of a dispatcher using video cell phones can improve the quality of chest compressions compared with verbal dispatcher instructions in the setting of COCPR by untrained laypersons.32 Another similar simulation trial showed that a CPR video clip stored in cellular phones can improve the performance of chest compressions during COCPR.15 Visual feedback may help to overcome the handicaps of verbal instruction, but it may have several limitations in the real world. Video instruction can delay the initiation of chest compression, and watching the video may be difficult while performing chest compressions.15 ,32 Most of all, a phone with video function may not be available to laypersons in many situations.
Efficacy of metronome sounds during COCPR with dispatcher guidance
The faster chest compression rate during CPR is associated with improvement of haemodynamic parameters and increase of survival independently.19 ,33 One of the most notable findings of this study was that less than 20% of the CG (given conventional verbal instructions) could deliver an accurate compression rate (100–120/min). However, nearly all the bystanders in the MG could deliver an accurate rate of chest compressions. As the metronome is a cheap and simple device, EMS can easily set the sound guidance system. Any kind of phone (wired or wireless) can play metronome sounds via a phone speaker, and all laypersons can receive real-time feedback of the metronome sounds during DA-COCPR. Therefore, we assume that a dispatch protocol with metronome sound guidance may be one of the methods to improve the quality of COCPR by untrained bystanders in the future.
Limitations of metronome sound guidance
Like the various reports of another simulation study using metronomes,16–18 we could not ensure sufficient compression depth, accurate hand position or fully released chest compressions. Some studies have shown that metronome-guided chest compressions were associated with a relatively shallow depth of chest compression.16 ,17 The current study showed a slightly shallower mean depth of compression in the MG than in the CG without statistical significance. Moreover, the MG showed a higher proportion of shallow compressions (depth <38 mm)24 than the CG. No studies have fully explained why chest compressions under metronome sound guidance are associated with relatively shallow chest compression depths. We assume that the relatively shallow compression depth can be attributed to the relative increase in the number of total chest compressions. The increase in the number of chest compressions in the MG may have increased the rescuers’ fatigue and, therefore, adversely affected the depth of chest compression. Rescuers develop fatigue earlier during COCPR than conventional 30 : 2 CPR, and the decrease in chest compression quality (especially compression depth) started early, after 1 min of CPR.34 The MG delivered a higher number of chest compressions than the CG over 4 min of COCPR, and the rescuers’ fatigue may have had a greater effect in the MG than in the CG. Another possible explanation is that the metronome sound guidance itself could have adversely affected the chest compression depth. Without the metronome guide, untrained rescuers performed the chest compressions with maximum effort. However, with the metronome, the rescuers performed chest compressions while concentrating on the rhythm, resulting in each compression not being performed with maximum effort.
To improve the survival rate of cardiac arrest victims, providers should perform chest compressions faster than 100 compressions per minute and deeper than 5 cm. During the DA-COCPR, metronome sound can serve for higher chance of correct compression rate, but may sacrifice the compression depth. We could not verify the overall net effect (increased rate and decreased depth than conventional DA-COCPR) of metronome sound-guided DA-COCPR in the current study. Further researches are warranted in future.
Limitations of the study
There are some limitations to this study. First, most of the participants were 20–40 years of age. The subjects did not consist of the elderly, who most often suffer from OHCAs.24 ,35 It may be difficult for these older persons to understand the metronome guidance system, and different results may be shown in this age group. Second, this study is not a true out-of-hospital CPR, but was conducted in a simulated situation, and therefore, the study environment might not have reflected the real stress of the situation of an OHCA or the variations in chest stiffness or anatomy of real human victims. In particular, the environmental noise at the scene of an OHCA may interfere with the communication and metronome sounds via a speaker, but we could not simulate this noisy environment, which happens occasionally in the real world.
Conclusions
Metronome sound guidance via a phone speaker during DA-COCPR for the untrained bystanders improved the rate of chest compressions in the current simulation trail. However, metronome sound-guided DA-COCPR was associated more with shallow chest compressions (compression depth <38 mm) than the conventional DA-COCPR in a manikin model.
Acknowledgments
We thank all residents of the Gyeongsang-Namdo, Republic of Korea who participated in this simulation trial. This work was supported by Konkuk university in 2012. We thank all residents of the Gyeongsang-Namdo, Republic of Korea who participated in this simulation trial.
References
Footnotes
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Contributors SOP established the main conception and, SOP and SYH designed this study. Each author took part in procedure of simulation trials (JKH and JHL), analysis and interpretation of data (all authors), and participated in writing and correcting the manuscript (SOP, SYH, JY and DHS). All authors read and approved the manuscript. SYH takes responsibility for the paper as a whole.
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Competing interests None.
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Ethics approval Changwon Samsung Hospital, Sungkyunkwan University's Institutional Review Board.
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Provenance and peer review Not commissioned; externally peer reviewed.