Sudden cardiac death is the leading cause of cardiovascular related death in Europe.1 Up to 84% of out-of-hospital cardiac arrests (OHCA) are witnessed by bystanders, but bystander-cardiopulmonary resuscitation (CPR) is initiated in less than 28% of cases prior to the arrival of emergency medical services (EMS).2,3 Outcome and long-term neurologic recovery after OHCA is significantly improved if bystander-CPR was performed.2,4,5 On the other hand, any delay in CPR results in poor prognosis.6 Although survival rates for OHCA have not improved significantly over the last 30 years in most European countries, some subgroup analyses revealed advantages for bystander-CPR, for ventricular fibrillation, and witnessed cardiac arrest.7,8
A primary cardiac cause is the most common mechanism of arrest in adults, but respiratory and other mechanisms are important concurrent factors.9–11 The relative importance of oxygenation depends on patient characteristics and the phase of arrest.12
Telephone-assisted CPR by the EMS dispatch service can improve outcome by reducing hesitancy and improving CPR quality.13–16
Initial dispatcher explanations and instructions are time consuming (especially if chest compressions and rescue ventilation are included) and can delay the start of resuscitation. In contrast, uninstructed CPR (U-CPR) allows immediate CPR but quality may be reduced. As a compromise, dispatcher-assisted compression-only CPR (DACO-CPR) can be performed with a shortened initial instruction phase but reduced CPR-quality because of lack of rescue-ventilation. Thus, the optimal technique for bystander-CPR has to be determined.17,18
We hypothesised that dispatcher instructions for bystanders to provide chest compression alone would result in improved CPR quality as compared with CPR without instructions and dispatcher-assisted chest compression along with rescue breathing.
The study was a prospective randomised controlled single-blinded manikin trial conducted in a university hospital. The study was approved by the local Ethics Committee (registration number: 10-333; 31 January 2011) and conducted from 1 July 2012 to 30 September 2012. Written informed consent was obtained from each participant prior to inclusion.
Sixty laypersons between 18 and 65 years were recruited. Medically educated individuals, medical professionals, those who had undergone more than basic life support training and pregnant women were excluded. Data on sex, age and date of attendance at basic life support training were recorded. The flow diagram according to the Consolidated Standards of Reporting Trials (CONSORT) Statement can be found in the supplement.
Study setting and group assignment
The Ambu Man W (Ambu GmbH, Bad Nauheim, Germany) was used as a manikin in the present study. To evaluate the quality of CPR, video surveillance was installed (Samsung, Seoul, South Korea). Data on CPR quality was collected via Ambu CPR Software Version 3.0.6 (Ambu GmbH, Bad Nauheim, Germany). Data were processed with Excel (Version 14.0; Microsoft Corp., Redmond, USA). To make an emergency call, a telephone connection using a Gigaset AL 275 Duo (Siemens AG, Munich, Germany) was established.
Each participant was randomly assigned using sealed envelopes to one of three different groups: U-CPR, compression-only dispatcher-assisted-CPR and full dispatcher-assisted-CPR including rescue ventilation (DAF-CPR) according to a standardised protocol designed according to the European Resuscitation Council (ERC) Guidelines 2010.19 Each participant received a standardised introduction. All participants were familiarised with the simulated environment including information about the confrontation with a simulated medical emergency situation including a manikin acting as the victim, and being able to elicit signs of life if present. In addition, all participants were instructed to use the mobile phone provided to make an emergency call if requested. Further instructions were given according to the participant's assigned group. During the emergency call, the EMS was dispatched and the test period started. The experiment was stopped after 8 min, based on the mean period of time for an EMS-crew to arrive in Germany. All data were collected by the applied equipment (manikin and software) using a form to ensure comprehensive data capture for each participant. In addition, we used the video surveillance data to assess the correct hand positioning for CPR and head-tilt for ventilation by two independent investigators.
The test period started at the disposition of the ambulance by the dispatcher and stopped after 8 min. During this time the following parameters were collected: no-flow-time (NFT), defined as the time without effective compression (i.e. break of more than 2 s or compression depth less than 20 mm); compression depth as an arithmetical mean over the whole test period; total number of compressions; compression frequency; correct hand positioning; correct release after compression; minute respiratory volume.
For sample size calculation we performed a pilot study with five participants and this suggested a minimum study group size of 16 (α = 5%, β = 80%). Data are presented as means ± standard deviation. To compare different groups, we used Student's t test and a P less than 0.05 was considered significant. For non-parametric, dichotomous data the χ2 test was used.
60 volunteers (33 men, 27 women) were included as participants and randomised. Two participants had to be excluded for technical reasons (one participant each in group, DACO-CPR and DAF-CPR). No significant differences were found amongst the members of the three groups regarding age or date of basic resuscitation training (Supplement, https://links.lww.com/EJA/A89).
The NFT of the DACO-CPR group (99.8 ± 70.7 s) was significantly shorter compared with both the U-CPR group and the DAF-CPR group (Fig. 1). The initial-NFT, representing mainly the instruction phase (NFT from beginning of the test period to the start of a continuous resuscitation), was lowest in the U-CPR group (5.4 ± 4.5 s) compared with both other groups. However, the initial-NFT in the DACO-CPR is significantly lower compared with the DAF-CPR group. Owing to the low NFT in the DACO-CPR group, the proportion of initial-NFT to NFT is significantly lower compared with the other groups (Fig. 2).
Most compressions were performed in the DACO-CPR group (512.1 ± 180.1); the compression frequency was significantly higher compared with both other groups (Fig. 3). Compression depth was not statistically different amongst all three groups and there was no significant difference in the fraction of correct compressions with a depth between 50 and 60 mm. Accordingly, there was no significant difference in the mean compression depth amongst all three groups (Fig. 4).
Hand position and compression release
No difference was found in the number of compressions with a wrong hand position. The lowest fraction of compressions with wrong hand positioning was found in DACO-CPR group, followed by the U-CPR group, and the DAF-CPR group. No significant difference was found concerning missing decompression.
For the total number of ventilation attempts, a significant difference was found between both groups: U-CPR 37.4 ± 18.3 and DAF-CPR 23.3 ± 5.0 (P
Comparing the U-CPR and DAF-CPR group there were no significant differences in the applied respiratory volume. However, highest respiratory volume was administered in the U-CPR group. The total amount of correctly performed ventilation attempts related to the tidal volume administered was low in the U-CPR and the DAF-CPR group (Figs 5 and 6).
All tables with results including the related tests of significance can be found in the supplement (https://links.lww.com/EJA/A89).
In the present manikin study, DACO-CPR resulted in the best quality of CPR as evidenced by superior compression frequencies and reduced NFT in comparison with U-CPR and full dispatcher-assisted CPR with rescue ventilation. The full dispatcher-assisted CPR with a longer initial instructing phase (initial NFT) did not result in enhanced CPR quality or an optimised compression depth.
In 2000, Hallstrom et al.20 analysed the influence of different dispatcher-assisted CPR variations on the outcome after OHCA. They could not find a significant difference between conventional CPR and compression-only-CPR but recommended compression-only-CPR as an option for medical laypersons. The time needed for adequate instructions by the dispatcher in their study was comparable to our findings: according to Hallstrom et al.20 dispatcher instructions for a full T-CPR took 1.4 min more than guidance for compression-only-CPR. In the present study a 2.3-fold increase in NFT comparing DACO-CPR and DAF-CPR was found. Other studies show a significant delay of CPR because of the complexity of instructions for a full dispatcher-assisted-CPR compared with compression-only-T-CPR.21,22 Delays because of dispatchers’ instructions extend the initial NFT but may optimise global NFT by enhancing CPR-performance. Each interruption of compression leads to a decrease in the probability of success.23 The results of our study show that compression-only-CPR best fits the recommendation of the ERC to keep the NFT as low as possible.
Compression depth and positioning
In the present study only 17.2 to 31.5% of all compressions met the 2010 guideline recommendations and there was no significant difference amongst groups. We could not find a difference in hand positioning or correct release amongst the three groups. Increased compression depth is associated with a higher chance of return of spontaneous circulation24–26 and should be deeper than 42 mm,27 and indeed the ERC recommends a compression depth of 50 to 60 mm.28
Compression frequency in the DACO-CPR group was significantly higher compared with both other groups. The compression frequency is an independent factor in the chance of return of spontaneous circulation and patient outcome.29,30 Nevertheless, a mean frequency of 66 compressions per minute (DACO-CPR group) is definitely low and thus keeping a compression frequency within the recommended range is an essential component of dispatcher protocols.
In the U-CPR group, an average of 37 ventilation attempts led to a single successful ventilation (3.1%) within the recommended tidal volume of 500 to 600 ml, whereas in the DAF-CPR group 23 attempts led to 0.4 (1.6%) correct ventilations. Analysis of the video records revealed an inadequate head tilt as one major reason for ventilation failure. In contrast, prevention of ‘excessive’ ventilation is one measure of good quality resuscitation.31 In our study, we could show that ventilation by medical laypersons led to tidal volumes over 600 ml in 36.9% (U-CPR group), compared with 26,2% when supported by dispatcher's guidance (DAF-CPR group). Studies in animals32–34 and humans9,10,35–37 suggest no definitive proof of a benefit from ventilation during CPR. In most of these studies, CPR without ventilation was equivalent or superior to CPR with rescue ventilation although this benefit was often inconclusive.38 Three subsequent studies compared outcome of DACO-CPR and CPR with rescue ventilation20,39,40: all trials favoured compression-only-CPR, but an assessment of which dispatcher-assisted CPR method is superior was inconclusive.38 Ventilation in an OHCA setting done by medical laypersons is known to be ineffective22 and this is confirmed in our study. Continuous feedback or frequent advice by the dispatcher may be more effective.
The study is of a manikin rather than in vivo but allowed consistent measurements avoiding clinical variation and confounding factors. Such a simulation study does not allow prediction of outcome and our results will have to be verified by clinical outcome studies.
In the present study, best quality of CPR was achieved by DACO-CPR because of superior compression frequencies and reduced NFT. Furthermore, no evidence was found that quality of ventilation was enhanced by dispatcher instructions. Our findings indicate that emergency medical dispatchers should primarily instruct compression-only CPR. The use of a full dispatcher-assisted CPR protocol should be reserved for cases that can be identified quickly as likely to benefit from ventilation.
Acknowledgements relating to this article
Assistance with the study: none.
Financial support and sponsorship: none.
Conflicts of interest: none.
Presentation: preliminary data for this study were presented as a poster presentation at the European Society of Anaesthesiology (ESA) Euroanaesthesia 2014, Stockholm.
Comment from the Editor: BWB is an associate editor of the European Journal of Anaesthesiology.
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