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Differing operational outcomes with six commercially available automated external defibrillators
Resuscitation 62 (2004) 167–174
Differing operational outcomes with six commercially available automated external defibrillators Roman Fleischhackl, Heidrun Losert, Moritz Haugk, Philip Eisenburger, Fritz Sterz, Anton N. Laggner, Harald Herkner∗ Department of Emergency Medicine, General Hospital, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria Received 30 December 2003; received in revised form 18 March 2004; accepted 24 March 2004
Abstract Introduction: In general automated external defibrillators (AED) are handled easily, but some untrained lay rescuers may have major problems with the use of such products. This may result in delayed shock delivery and delay in basic life support (BLS) after use of the AED. To study the effect of voice prompts and design solutions we tested the time from the first shock to the initiation of BLS for six defibrillators available in Austria. Methods: Volunteers, who had no AED training, were evaluated to see when they delivered the first shock and how often BLS was started after the voice prompts were given by the defibrillators. Results: Time to first shock delivered ranged from 78 (95% CI: 68–89) to 128 (95% CI: 110–146) s. The defibrillator-type had a significant influence on the time to first shock delivered (P < 0.0001). The proportion of volunteers who started BLS after defibrillation ranged from 93 to 33% and differed significantly between the AEDs used (P < 0.03). Conclusions: We demonstrated that there are significant differences between AEDs, concerning important operational outcomes like time to first shock and the start of BLS. Further research and development is urgently required to optimise user-friendliness and operational outcomes. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Automated external defibrillator; Basic Life support; Bystander CPR; Out-of-hospital CPR
Resumo Introdução: Na generalidade, os desfibrilhadores automáticos externos (DAE) são facilmente manuseáveis, mas alguns socorristas leigos, sem treino podem ter problemas sérios na utilização de tais aparelhos. Isto pode resultar num atraso na administração do choque e atraso no suporte básico de vida (SBV) após a utilização do DAE. Para estudar o efeito das ordens vocais e desenvolver soluções testámos o tempo do primeiro choque ao in´ıcio do SBV em seis dos desfibrilhadores dispon´ıveis na Áustria. Métodos: Voluntários, sem treino em DAE, foram avaliados para verificar quando administravam o primeiro choque e com que frequˆencia era iniciado o SBV depois de dadas as instruções pelo DAE. Resultados: O tempo até ao primeiro choque variou de 78 (95% CI: 68–69) a 128 (95% CI: 110–146) s. O tipo de desfibrilhador teve influˆencia significativa no tempo para administração do primeiro choque (P < 0.0001). A proporção de voluntários que iniciou SBV após a desfibrilhação variou de 93 a 33% e diferiu significativamente entre os DAE utilizados. (P < 0.03). Conclusões: Demonstramos que há diferenças significativas entre DAE’s, implicando diferenças operacionais importantes como o tempo até ao primeiro choque e in´ıcio de SBV. É necessária investigação adicional para, com urgˆencia, optimizar a facilidade de utilização e os resultados operacionais. © 2004 Elsevier Ireland Ltd. All rights reserved. Palavras chave: Desfibrilhador automático externo (DAE); Suporte básico de Vida (SBV); RCP por leigo; RCP extra-hospitalar
Resumen Introducción: En general los desfibriladores automáticos externos (AED) son fácilmente manipulables, pero algunos reanimadores legos no entrenados pueden tener mayores problemas con el uso de tales productos. Esto puede resultar en retraso en la entrega de las descargas desfibriladoras y retraso en el soporte vital básico (BLS) después de usar el AED. Para estudiar el efecto de las indicaciones audibles y soluciones de diseño, medimos el tiempo desde la primera descarga hasta el inicio del BLS en seis desfibriladores disponibles en Austria. ∗
Corresponding author. Tel.: +43-1-40400-1964; fax: +43-1-40400-1965. E-mail address: [email protected] (H. Herkner).
0300-9572/$ – see front matter © 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.resuscitation.2004.03.018
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Métodos: Voluntarios, quienes no ten´ıan entrenamiento en AED, fueron evaluados para ver cuando entregaban la primera descarga y con que frecuencia iniciaban el BLS después que de las indicaciones audibles de los desfibriladores. Resultados: El tiempo hasta la primera descarga varió en un rango de 78 (95% CI: 68–89) a 128 (95% CI: 110–146) segundos. El tipo de desfibrilador tuvo una influencia significativa sobre el tiempo a la primera descarga (P < 0.0001). La proporción de voluntarios que iniciaron BLS después de desfibrilar varió en un rango de 93 a 33% y difirieron significativamente entre los AEDs usados (P < 0.03). Conclusiones: demostramos que hay diferencias significativas entre los AEDs, que conciernen resultados operacionales importantes como el tiempo a la primera descarga y el inicio del BLS. Se requiere urgentemente ulterior investigación y desarrollo para optimizarla facilidad de uso y los resultados operacionales. © 2004 Elsevier Ireland Ltd. All rights reserved. Palabras clave: Desfibrilador automático externo (DAE); Soporte vital Básico (SVB); Reanimación por testigos; RCP extrahospitalaria
1. Introduction Many out-of-hospital cardiac arrest victims suffer from mild to severe, very often irreversible, neurological damage [1,2]. Like mortality, also neurological impairment can be decreased by early effective resuscitation, whether by lay or professional rescuers [3]. The success of out-of-hospital cardio pulmonary resuscitation (CPR) attempts depends strongly on the period that has elapsed between the occurrence of a life threatening event and the initiation of bystander help [4]. The most important link in the chain of survival is the bystander who witnesses the collapse [5]. The chance of successful CPR nearly correlates linearly with the duration of the interval until basic life support (BLS) and early defibrillation are given [6]. Most citizens worry about making mistakes in bystander CPR, and therefore hesitate to provide immediate support [7]. Automated external defibrillators (AED) can potentially help to quell such anxieties and hesitation. A tremendous amount of public resources have been focused on improving cardiac arrest survival in public places, yet most out-of-hospital cardiac arrest incidents occur in private residences [8]. Therefore, AEDs are becoming increasingly more available for lay responders in Austria, since the Austrian Red Cross initiated a nation-wide public access defibrillation (PAD) project in 2001 [9]. Further, there is a focused strategy initiative, where relatives of high risk patients, like cardiac arrest survivors, are supplied with AEDs [10]. Even though the devices are easily handled in general [11], untrained lay rescuers may have major problems with the use of particular products [12]. Valuable time may be lost, impairing survival and good neurological outcome after cardiac arrest [13,14]. Unambiguous and intuitive understanding of instructions is crucial for time-saving action. Understanding of specific visual and linguistic instructions may depend on cultural particularities. Since most AEDs are produced by international companies for use in many countries, translations of instructions must allow for cultural differences. Not all technical solutions, guiding figures or voice prompts given by the different AEDs may be clear enough for everyone to provide proper BLS. Lay rescuers may become confused by AED prompts, which may result in delayed shock delivery and delay in BLS after the delivered shocks. The current study aims to compare all six defibrillators available in Austria for time to the first shock given and the
initiation of BLS by lay people who are completely untrained in the use of an AED.
2. Methods and study design We included volunteers from a large company and one school in Vienna as lay rescuers, who had no experience with an AED beforehand and who consented to participate. The study was carried out by members of the Department of Emergency Medicine at the University General Hospital of Vienna. We used all types of AEDs available in Austria at the time. These were training defibrillators with no electrical discharge, from the six companies represented in Austria. Standardised equipment consisted of the allocated AED, a face shield and latex gloves. At the beginning of the experiment dressed manikins (Recording Resusci AnneTM CPR Manikin, Laerdal Corporation, Norway) were put in supine position on the floor. We performed the experiment in an isolated area, so that volunteers were not aware of the action taken by their predecessors. We chose a parallel group design of six groups and randomly allocated the six types of AEDs. Randomisation was performed by using a random number generator from a spreadsheet programme. According to this random list we produced consecutively numbered sheets revealing the name of the AED allocated. To ensure allocation concealment the numbered sheets were folded and sealed with staples. Immediately after a volunteer gave informed consent, a folded sheet was opened, and the evaluation was started. After assignment to an AED, volunteers were instructed by investigators that they were going to be exposed to a simulated cardiac arrest situation and that they should attempt every action that they would consider to be helpful. After the introduction, no further interaction between the investigators and the volunteers was allowed. The experiment was videotaped and the data were documented on a standardised evaluation form. The time elapsed from start to the first shock delivered (‘time to first shock’) was measured in seconds. Furthermore, we documented whether BLS was started at all after delivery of the first shock. Malpositioning of the electrodes, misunderstanding of voice-prompts or other difficulties and events were recorded on the data-sheets. The positioning of the pads
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was scored as being correct when attached approximately in the axis of lead II [12]. The principle outcome variable being studied was time to first shock delivered. The secondary outcome was how often BLS was started according to the voice prompts from the defibrillators. Due to practical considerations and the largely objective nature of the outcome variables no formal blinding was performed. The trial was stopped after at least one shock was given and after BLS was started. The simulation was also terminated if volunteers indicated no further action, or after 5 min without any action, whichever came first. It is understood that feedback was given and retraining was offered to the lay helpers, but not until after the end of the experiment to avoid contamination of the data.
2.1.4. AccessTM (Access Cardio Systems, Concord, Massachusetts, USA) Electrodes not pre-connected, two adhesive pads in separate plastic liners, stored in the lid of the device, pre-selected simulation algorithm. After the last prompt (the one to start BLS) the device starts with a new simulation cycle and therefore it had to be turned off immediately after the last voice prompt, not to confuse volunteers.
2.1. AEDs and AED training units studied (see Fig. 1)
2.1.6. HS1TM (Philips Medical System, Andover, Seattle, USA) Electrodes pre-connected, two adhesive pads in one plastic liner, stored in a cartridge included in the device, pre-selected scenarios for CPR simulation, device recognises attachment of the electrodes via an impedance simulating metal stripe.
2.1.1. LIFEPAK CRTTM (Medtronic, Minneapolis, USA) Electrodes pre-connected, two adhesive pads in one plastic liner stored in the device, patient simulation through infrared remote control 2.1.2. Fred easy® (Schiller AG, Baar, Switzerland) Electrodes not pre-connected, two adhesive pads in separate plastic liners stored in the bag of the device, patient simulation through infrared remote control. 2.1.3. AED+PLUSTM (Zoll Medical, Chelmsford, Massachusetts, USA) Electrodes pre-connected, one large adhesive electrode, stored in the device, remote control via cable connection.
2.1.5. Power Heart Training UnitTM (Cardiac Science Inc., Irvine, California, USA) Electrodes pre-connected, two adhesive pads in one plastic liner, stored in the device, simulation through infrared remote control.
2.2. Statistical analysis Data are presented as a number and a percentage, the mean and 95% confidence intervals, or the mean and standard deviation if not otherwise stated. The groups allocated to the six defibrillators were regarded as independent. Baseline data including age, gender and time from last CPR training were tabulated. Baseline data were not compared using
Fig. 1. The six automated external defibrillators (AED) currently commercially available in Austria, which were used in the experiment. Rear row (left–right): LIFEPAK CRTTM (Medtronic, Minneapolis, USA), Fred easy® (Schiller AG, Baar, Switzerland) AED+ PLUSTM (Zoll Medical, Chelmsford, Massachusetts USA); Front row (left–right): AccessTM (Access Cardio Systems, Concord, Massachusetts, USA), Power Heart Training UnitTM (Cardiac Science Inc., Irvine, California, USA), HS1TM (Philips Medical System, Andover, Seattle, USA).
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hypothesis testing. Upon inspection we did not find major baseline differences, indicating reasonably valid randomisation. The principle outcome variable was time to first shock. Data were near the normal distribution in all groups as tested by the Kolomgorov Smirnov test and visual inspection of histograms. Hence, groups were compared by one-way ANOVA, testing the null hypothesis that there is no difference between the groups. The secondary outcome was how often BLS was started after the according voice prompt by the defibrillators. The proportions were compared between the defibrillator groups employing χ2 -statistics. Two post-hoc analysis sets were performed to validate our findings. (1) To test whether the gender influenced the primary or secondary outcome, we used the Mann–Whitney U-test and a χ2 -test. (2) To test whether the time elapsed from the last CPR training influenced primary or secondary outcome we used linear correlation and a χ2 -test. SPSS for Windows 10.0.7 (SPSS Inc., Chicago, IL) was used for data management and processing. A two-sided P-value < 0.05 was considered statistically significant.
3. Results Overall, 90 volunteers out of 120 consented to participate, and all of those who consented completed the experiment. Twenty-seven (30%) of the volunteers were female. Age ranged from 15 to 55 years with an average of 28 ± 16 years. Lay responders had attended their last CPR training 6.4 ± 6 years ago (range: 0.5–25), none had been trained to use an AED. Two volunteers had never attended CPR training before.
3.1. Main outcome Time to first shock according to defibrillator type is presented in Fig. 2 and ranged from 78 (95% CI: 68–89) when the CR+TM was used to 128 (95% CI: 110–146) s when AED+TM was operated. As assessed by ANOVA, time to first shock was significantly different between the six AEDs (P > 0.0001). Not all users reached the primary goal of delivering a shock. One device was turned off unintentionally (see “specific findings” of Fred easy®), on two occasions the shock was impaired by not removed clothing and/or plastic liner of the pads (AED+TM ). One volunteer was confused by the device and gave up without providing any further help (AED+TM ). 3.2. Secondary outcome The proportion of volunteers who started BLS after defibrillation is presented in Fig. 3. This proportion ranged between AED groups from 93% (14 out of 15) to 33% (5 out of 15). The proportion of volunteers who started BLS after defibrillation in the AED groups, also differed significantly (P < 0.03). The results of the defibrillator “AccessTM ” are marked with an asterisk in Fig. 3 due to a procedural peculiarity of the training device. After completion of the first shock, the training simulation started again from the very beginning, shortly after its last prompt: “in absence of vital signs start cardio-pulmonary-resuscitation”. Therefore, investigators had to turn off the device after this prompt and ask lay helpers what they would do next. Once the device was turned off, 13 out of 15 lay responders stated, that they would start
Fig. 2. Defibrillator type and the time to first shock (seconds, mean and 95% CI). In three occasions with AED+TM and in one occasion with Fred easy® volunteers failed to deliver a shock.
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Fig. 3. The number of volunteers who started BLS after shock according to the defibrillator used in random order. ∗Access had limited comparability to other defibrillators, because the training-device had to be turned off after the last voice prompt.
BLS after the shocks. Hence, regarding the secondary end point, the “AccessTM ” AED cannot be compared to the other AEDs directly. 3.3. Influence of gender, age and time since last CPR training on the use of an AED There was no significant association between gender and time to first shock (P < 0.7) and the proportion of BLS started after the shocks (P < 0.41). There was also no significant association between the time since the last CPR training and time to first shock delivered (P < 0.69) or whether BLS was started after the shocks (P < 0.96). 3.4. Miscellaneous Findings Electrodes were not attached correctly in nine cases (4 Power HeartTM , 2 AED+TM , 2 AccessTM , 1 CR+TM ). Volunteers stated that they were confused about the electrode positioning in 14 cases (5 Power HeartTM , 3 AccessTM , 2 Fred easy®, 2 CR+TM , 1 AED+TM ) but placed the pads correctly. In two cases the lay rescuers did not remove the plastic liner from the pads (1 Power HeartTM , 1 AED+TM ). Two volunteers in the AED+ group did not remove clothing from the manikin’s chest before attaching the electrodes. The information button provided by the HS1TM was pressed by all users (15 out of 15) to be guided through BLS.
4. Discussion We could demonstrate clearly that there are significant differences between the AEDs tested, with regard to the time to first shock. These differences were not only statistically significant, but also of clinical significance. Looking at the time to first shock, the mean difference between the AEDs was as much as 50 s. This is of particular interest, because the time with the AED until the first shock is delivered is most likely time without chest compressions and therefore no-flow time [14]. Hence, this length of time could lead to increased mortality at the rate of almost 10% per minute [4]. Keeping this time to a minimum must be one of the major aims in developing AEDs. Recently, it was reported, that AEDs produced important delays in cardiac arrest situations [14,15]. It was beyond the scope of our study to identify prospectively the factors responsible for these important operational differences, but this heterogeneity should prompt further research. We also found significant heterogeneity in the proportion of BLS started after unsuccessful shocks. The maximum difference was as much as nine failures to start BLS in 15 trials. Theoretically, this could be translated into a relative risk reduction of 90%, when comparing the best and the worst AED, or a number needed to treat of two. Due to the importance of bystander BLS [6], a safe and easily understandable guide through the following steps after shock delivery is of utmost importance. Most volunteers in our experiment had attended CPR training before. This might be due to the fact that first aid
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education is mandatory when applying for a driving license in Austria. Former studies showed quite similar periods before the first shock was provided by untrained lay responders [12]. The large number of successfully simulated defibrillations also strengthens former findings of the simple use of AEDs in general, even by school children [11]. According to current knowledge neither helpers nor patients were endangered through the first aid efforts including defibrillation during our experiment [16]. Therefore, even untrained helpers are able to provide early defibrillation safely. We assumed that effects of the design had been extensively tested in advance for all AEDs by the respective companies. Given the simple aim of an AED to deliver appropriate shocks and guide BLS, it is indeed interesting that we could find differences in the operational outcome. It seems obvious, that the design of the device itself creates these differences. Most likely the key factors for failure were the content and volume of voice prompts and the arrangement of the buttons. We had the impression that some prompts were easier to understand for first time users, whereas others were not. In the absence of any correlation between the time since last first aid training and the initiation of BLS after shock, we conclude that volunteers placed a great deal of trust in the devices prompts. Once confused by a prompt, many of the volunteers stopped their BLS, despite former training. We could observe difficulties if voice prompts were given too quickly in a sequence. Our impression also was, that confusion could occur if the pictures were too numerous or too small. The scenario of our experiment was a semi-public place comparable to the environment of a shopping mall. Though not extreme, the presence of voices and light conditions from a big window seemed to have an effect on the operation of the AEDs. Therefore, it should be assessed if the devices could be used in bright or low light conditions. Also, loud and disturbing surroundings should not detract from the application and operation of an AED. 4.1. Limitations Even though AEDs and their user-friendliness turned out to vary in our experiment, the relevance for real cardiac arrest situations remains unclear. Volunteers knew about the simulated situation and in general showed very calm behaviour, which is unlikely to be the case in a real event. However, as AEDs have been used infrequently by lay-rescuers to date [17], it is currently not possible to gain necessary patient numbers to compare the effectiveness of different AEDs in clinical circumstances. Experimental work is probably the best we can have at the moment. We did not investigate if BLS was performed in an effective way after defibrillation. Possible advantages caused by special interactive voice prompts, for example as given by the AED+TM are therefore not reported in this trial.
Because of the absent impedance in the manikins, investigators had to push a button, to simulate the attached electrodes. Even though being aware of this problem, this procedure may have caused a minor delay. 4.2. Specific findings in the AEDs 4.2.1. LIFEPAK CRTTM (Medtronic, Minneapolis, USA) Users of the CR+TM defibrillated very quickly. The narrow 95% CI indicates, that many users were guided through the defibrillation process well. The flashing shock button was visible without problems in all light conditions. Voice prompts are given loud and clearly. The two clearly marked electrodes guided users to the correct electrode position. The device prompts the user to start BLS by using the abbreviation “BLS”, which is commonly unknown. This may be why only five out of 15 volunteer helpers started BLS after the initial defibrillation. Helpers reacted in a confused manner by pressing the shock button several times, turning the device off and on or by aborting their bystander support. 4.2.2. Fred easy® (Schiller AG, Baar, Switzerland) Pictures on the electrodes show the users how to attach the pads in a correct position. Lay helpers liked the advice to start BLS or to bring the patient in recovery position depended on the presence of vital signs. Voice prompts that were not understood could be read on a display in addition. The device did not start the ECG analysis on its own. Therefore, users were prompted to press the on/off button after attaching the pads. One user pushed the button until the device was turned off and no shock could be delivered. This was the only device where users had to push an analyse button ( = on/off button). In presence of a non shockable rhythm the device prompts users to start BLS by giving two breaths and compressing the chest 15 times if they were not able to detect vital signs. In the presence of vital signs the recovery position is recommended by the AED. 4.2.3. AED+TM (Zoll Medical, Chelmsford, Massachusetts, USA) The single electrode of the AED+ PLUSTM seems to prevent users from attaching the pads in an incorrect position. If performing the chest massage too weakly the AED+ gives feedback to press deeper. Also the frequency of the chest compressions is advised by a metronome. These feedback features were not tested during our experiment with the training device, therefore maybe existing advantages are not highlighted here. One user failed to open the AED. Another volunteer needed a lot of time to find out how to open the device. Once opened, one participant tried to position the top of the AED under the manikins head unsuccessfully and lost valuable time. It seemed that the device prompted users too quickly and that optical signs were only understood after feedback and training. Two users did not undress the manikin to attach the electrodes. As the volume of the prompting voice of the training unit was quite low, some users had dif-
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ficulties hearing the prompts clearly. The button to switch on the device was not visible enough for all users. 4.2.4. AccessTM (Access Cardio Systems, Concord, Massachusetts, USA) This device was the smallest of the devices tested. Electrode positioning is indicated on the electrode package clearly. Once the package is opened, the guiding pictures are not clearly visible any more. The device prompts users to plug in the electrodes by saying: “Connect electrodes”. This prompt was not understood by all users, some thought that they had to attach the electrodes at that point and were unsure how to do this. The pictures shown on the pads are quite small and were not clearly visible for all volunteers. Some volunteers had problems with opening the lid, because the mechanism is not shown clearly. As already mentioned, the particular training programme of this device produced a peculiar situation for the interpretation of the further BLS guidance by restarting after the first shock instead of continuing the regular algorithm (see above). 4.2.5. Power Heart training unitTM (Cardiac Science Inc., Irvine, California, USA) Opening the lid activates this AED. Because the voice prompts did not start immediately after activation, some users closed the lid again, to search for an activation button. The voice prompt to attach the electrodes was misunderstood by three users concerning the position. These volunteers attached the electrodes directly to the manikin’s mamillae because the AED prompts: “Attach the electrodes to the patient’s chest”. Voice volume was low and the LEDs of the “flashing” button were too weak in daylight conditions. One volunteer did not remove packing material from the electrodes. 4.2.6. HS1TM (Philips medical system, Andover, Seattle, USA) This device guides the user with slow and clear prompts. Users stated that the different signed electrodes of this device were useful. It also provides an information button to get further instruction as to how to start and provide BLS. All users pressed this button and did exactly what the device prompted. The recommended heart compression rate given by a metronome was appreciated by the volunteers. Mouth to mouth ventilation was explained precisely as well as chest compression.
5. Summary We could demonstrate that there are significant differences between AEDs, concerning important operational outcomes such as the time to first shock and start of BLS. It seems to be likely that the design of the device itself accounts mainly for these differences, but the proof for that was beyond the scope of this study. Factors for failure may
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have been related to the content and volume of voice prompts and arrangement of buttons. Further research and development is urgently required to optimise user-friendliness and operational outcomes.
Acknowledgements We are indebted to the training centre of the Vienna Red Cross, for kindly supplying us with the manikins and other training material as well as to Medtronic Austria, Chemomedica Vienna, Zoll Medical, Schiller Austria, Marquette Hellige, and Philips Medical Systems for providing us with the AEDs and the training electrodes.
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Differing operational outcomes with six commercially available automated external defibrillators Roman Fleischhackl, Heidrun Losert, Moritz Haugk, Philip Eisenburger, Fritz Sterz, Anton N. Laggner, Harald Herkner∗ Department of Emergency Medicine, General Hospital, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria Received 30 December 2003; received in revised form 18 March 2004; accepted 24 March 2004
Abstract Introduction: In general automated external defibrillators (AED) are handled easily, but some untrained lay rescuers may have major problems with the use of such products. This may result in delayed shock delivery and delay in basic life support (BLS) after use of the AED. To study the effect of voice prompts and design solutions we tested the time from the first shock to the initiation of BLS for six defibrillators available in Austria. Methods: Volunteers, who had no AED training, were evaluated to see when they delivered the first shock and how often BLS was started after the voice prompts were given by the defibrillators. Results: Time to first shock delivered ranged from 78 (95% CI: 68–89) to 128 (95% CI: 110–146) s. The defibrillator-type had a significant influence on the time to first shock delivered (P < 0.0001). The proportion of volunteers who started BLS after defibrillation ranged from 93 to 33% and differed significantly between the AEDs used (P < 0.03). Conclusions: We demonstrated that there are significant differences between AEDs, concerning important operational outcomes like time to first shock and the start of BLS. Further research and development is urgently required to optimise user-friendliness and operational outcomes. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Automated external defibrillator; Basic Life support; Bystander CPR; Out-of-hospital CPR
Resumo Introdução: Na generalidade, os desfibrilhadores automáticos externos (DAE) são facilmente manuseáveis, mas alguns socorristas leigos, sem treino podem ter problemas sérios na utilização de tais aparelhos. Isto pode resultar num atraso na administração do choque e atraso no suporte básico de vida (SBV) após a utilização do DAE. Para estudar o efeito das ordens vocais e desenvolver soluções testámos o tempo do primeiro choque ao in´ıcio do SBV em seis dos desfibrilhadores dispon´ıveis na Áustria. Métodos: Voluntários, sem treino em DAE, foram avaliados para verificar quando administravam o primeiro choque e com que frequˆencia era iniciado o SBV depois de dadas as instruções pelo DAE. Resultados: O tempo até ao primeiro choque variou de 78 (95% CI: 68–69) a 128 (95% CI: 110–146) s. O tipo de desfibrilhador teve influˆencia significativa no tempo para administração do primeiro choque (P < 0.0001). A proporção de voluntários que iniciou SBV após a desfibrilhação variou de 93 a 33% e diferiu significativamente entre os DAE utilizados. (P < 0.03). Conclusões: Demonstramos que há diferenças significativas entre DAE’s, implicando diferenças operacionais importantes como o tempo até ao primeiro choque e in´ıcio de SBV. É necessária investigação adicional para, com urgˆencia, optimizar a facilidade de utilização e os resultados operacionais. © 2004 Elsevier Ireland Ltd. All rights reserved. Palavras chave: Desfibrilhador automático externo (DAE); Suporte básico de Vida (SBV); RCP por leigo; RCP extra-hospitalar
Resumen Introducción: En general los desfibriladores automáticos externos (AED) son fácilmente manipulables, pero algunos reanimadores legos no entrenados pueden tener mayores problemas con el uso de tales productos. Esto puede resultar en retraso en la entrega de las descargas desfibriladoras y retraso en el soporte vital básico (BLS) después de usar el AED. Para estudiar el efecto de las indicaciones audibles y soluciones de diseño, medimos el tiempo desde la primera descarga hasta el inicio del BLS en seis desfibriladores disponibles en Austria. ∗
Corresponding author. Tel.: +43-1-40400-1964; fax: +43-1-40400-1965. E-mail address: [email protected] (H. Herkner).
0300-9572/$ – see front matter © 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.resuscitation.2004.03.018
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Métodos: Voluntarios, quienes no ten´ıan entrenamiento en AED, fueron evaluados para ver cuando entregaban la primera descarga y con que frecuencia iniciaban el BLS después que de las indicaciones audibles de los desfibriladores. Resultados: El tiempo hasta la primera descarga varió en un rango de 78 (95% CI: 68–89) a 128 (95% CI: 110–146) segundos. El tipo de desfibrilador tuvo una influencia significativa sobre el tiempo a la primera descarga (P < 0.0001). La proporción de voluntarios que iniciaron BLS después de desfibrilar varió en un rango de 93 a 33% y difirieron significativamente entre los AEDs usados (P < 0.03). Conclusiones: demostramos que hay diferencias significativas entre los AEDs, que conciernen resultados operacionales importantes como el tiempo a la primera descarga y el inicio del BLS. Se requiere urgentemente ulterior investigación y desarrollo para optimizarla facilidad de uso y los resultados operacionales. © 2004 Elsevier Ireland Ltd. All rights reserved. Palabras clave: Desfibrilador automático externo (DAE); Soporte vital Básico (SVB); Reanimación por testigos; RCP extrahospitalaria
1. Introduction Many out-of-hospital cardiac arrest victims suffer from mild to severe, very often irreversible, neurological damage [1,2]. Like mortality, also neurological impairment can be decreased by early effective resuscitation, whether by lay or professional rescuers [3]. The success of out-of-hospital cardio pulmonary resuscitation (CPR) attempts depends strongly on the period that has elapsed between the occurrence of a life threatening event and the initiation of bystander help [4]. The most important link in the chain of survival is the bystander who witnesses the collapse [5]. The chance of successful CPR nearly correlates linearly with the duration of the interval until basic life support (BLS) and early defibrillation are given [6]. Most citizens worry about making mistakes in bystander CPR, and therefore hesitate to provide immediate support [7]. Automated external defibrillators (AED) can potentially help to quell such anxieties and hesitation. A tremendous amount of public resources have been focused on improving cardiac arrest survival in public places, yet most out-of-hospital cardiac arrest incidents occur in private residences [8]. Therefore, AEDs are becoming increasingly more available for lay responders in Austria, since the Austrian Red Cross initiated a nation-wide public access defibrillation (PAD) project in 2001 [9]. Further, there is a focused strategy initiative, where relatives of high risk patients, like cardiac arrest survivors, are supplied with AEDs [10]. Even though the devices are easily handled in general [11], untrained lay rescuers may have major problems with the use of particular products [12]. Valuable time may be lost, impairing survival and good neurological outcome after cardiac arrest [13,14]. Unambiguous and intuitive understanding of instructions is crucial for time-saving action. Understanding of specific visual and linguistic instructions may depend on cultural particularities. Since most AEDs are produced by international companies for use in many countries, translations of instructions must allow for cultural differences. Not all technical solutions, guiding figures or voice prompts given by the different AEDs may be clear enough for everyone to provide proper BLS. Lay rescuers may become confused by AED prompts, which may result in delayed shock delivery and delay in BLS after the delivered shocks. The current study aims to compare all six defibrillators available in Austria for time to the first shock given and the
initiation of BLS by lay people who are completely untrained in the use of an AED.
2. Methods and study design We included volunteers from a large company and one school in Vienna as lay rescuers, who had no experience with an AED beforehand and who consented to participate. The study was carried out by members of the Department of Emergency Medicine at the University General Hospital of Vienna. We used all types of AEDs available in Austria at the time. These were training defibrillators with no electrical discharge, from the six companies represented in Austria. Standardised equipment consisted of the allocated AED, a face shield and latex gloves. At the beginning of the experiment dressed manikins (Recording Resusci AnneTM CPR Manikin, Laerdal Corporation, Norway) were put in supine position on the floor. We performed the experiment in an isolated area, so that volunteers were not aware of the action taken by their predecessors. We chose a parallel group design of six groups and randomly allocated the six types of AEDs. Randomisation was performed by using a random number generator from a spreadsheet programme. According to this random list we produced consecutively numbered sheets revealing the name of the AED allocated. To ensure allocation concealment the numbered sheets were folded and sealed with staples. Immediately after a volunteer gave informed consent, a folded sheet was opened, and the evaluation was started. After assignment to an AED, volunteers were instructed by investigators that they were going to be exposed to a simulated cardiac arrest situation and that they should attempt every action that they would consider to be helpful. After the introduction, no further interaction between the investigators and the volunteers was allowed. The experiment was videotaped and the data were documented on a standardised evaluation form. The time elapsed from start to the first shock delivered (‘time to first shock’) was measured in seconds. Furthermore, we documented whether BLS was started at all after delivery of the first shock. Malpositioning of the electrodes, misunderstanding of voice-prompts or other difficulties and events were recorded on the data-sheets. The positioning of the pads
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was scored as being correct when attached approximately in the axis of lead II [12]. The principle outcome variable being studied was time to first shock delivered. The secondary outcome was how often BLS was started according to the voice prompts from the defibrillators. Due to practical considerations and the largely objective nature of the outcome variables no formal blinding was performed. The trial was stopped after at least one shock was given and after BLS was started. The simulation was also terminated if volunteers indicated no further action, or after 5 min without any action, whichever came first. It is understood that feedback was given and retraining was offered to the lay helpers, but not until after the end of the experiment to avoid contamination of the data.
2.1.4. AccessTM (Access Cardio Systems, Concord, Massachusetts, USA) Electrodes not pre-connected, two adhesive pads in separate plastic liners, stored in the lid of the device, pre-selected simulation algorithm. After the last prompt (the one to start BLS) the device starts with a new simulation cycle and therefore it had to be turned off immediately after the last voice prompt, not to confuse volunteers.
2.1. AEDs and AED training units studied (see Fig. 1)
2.1.6. HS1TM (Philips Medical System, Andover, Seattle, USA) Electrodes pre-connected, two adhesive pads in one plastic liner, stored in a cartridge included in the device, pre-selected scenarios for CPR simulation, device recognises attachment of the electrodes via an impedance simulating metal stripe.
2.1.1. LIFEPAK CRTTM (Medtronic, Minneapolis, USA) Electrodes pre-connected, two adhesive pads in one plastic liner stored in the device, patient simulation through infrared remote control 2.1.2. Fred easy® (Schiller AG, Baar, Switzerland) Electrodes not pre-connected, two adhesive pads in separate plastic liners stored in the bag of the device, patient simulation through infrared remote control. 2.1.3. AED+PLUSTM (Zoll Medical, Chelmsford, Massachusetts, USA) Electrodes pre-connected, one large adhesive electrode, stored in the device, remote control via cable connection.
2.1.5. Power Heart Training UnitTM (Cardiac Science Inc., Irvine, California, USA) Electrodes pre-connected, two adhesive pads in one plastic liner, stored in the device, simulation through infrared remote control.
2.2. Statistical analysis Data are presented as a number and a percentage, the mean and 95% confidence intervals, or the mean and standard deviation if not otherwise stated. The groups allocated to the six defibrillators were regarded as independent. Baseline data including age, gender and time from last CPR training were tabulated. Baseline data were not compared using
Fig. 1. The six automated external defibrillators (AED) currently commercially available in Austria, which were used in the experiment. Rear row (left–right): LIFEPAK CRTTM (Medtronic, Minneapolis, USA), Fred easy® (Schiller AG, Baar, Switzerland) AED+ PLUSTM (Zoll Medical, Chelmsford, Massachusetts USA); Front row (left–right): AccessTM (Access Cardio Systems, Concord, Massachusetts, USA), Power Heart Training UnitTM (Cardiac Science Inc., Irvine, California, USA), HS1TM (Philips Medical System, Andover, Seattle, USA).
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hypothesis testing. Upon inspection we did not find major baseline differences, indicating reasonably valid randomisation. The principle outcome variable was time to first shock. Data were near the normal distribution in all groups as tested by the Kolomgorov Smirnov test and visual inspection of histograms. Hence, groups were compared by one-way ANOVA, testing the null hypothesis that there is no difference between the groups. The secondary outcome was how often BLS was started after the according voice prompt by the defibrillators. The proportions were compared between the defibrillator groups employing χ2 -statistics. Two post-hoc analysis sets were performed to validate our findings. (1) To test whether the gender influenced the primary or secondary outcome, we used the Mann–Whitney U-test and a χ2 -test. (2) To test whether the time elapsed from the last CPR training influenced primary or secondary outcome we used linear correlation and a χ2 -test. SPSS for Windows 10.0.7 (SPSS Inc., Chicago, IL) was used for data management and processing. A two-sided P-value < 0.05 was considered statistically significant.
3. Results Overall, 90 volunteers out of 120 consented to participate, and all of those who consented completed the experiment. Twenty-seven (30%) of the volunteers were female. Age ranged from 15 to 55 years with an average of 28 ± 16 years. Lay responders had attended their last CPR training 6.4 ± 6 years ago (range: 0.5–25), none had been trained to use an AED. Two volunteers had never attended CPR training before.
3.1. Main outcome Time to first shock according to defibrillator type is presented in Fig. 2 and ranged from 78 (95% CI: 68–89) when the CR+TM was used to 128 (95% CI: 110–146) s when AED+TM was operated. As assessed by ANOVA, time to first shock was significantly different between the six AEDs (P > 0.0001). Not all users reached the primary goal of delivering a shock. One device was turned off unintentionally (see “specific findings” of Fred easy®), on two occasions the shock was impaired by not removed clothing and/or plastic liner of the pads (AED+TM ). One volunteer was confused by the device and gave up without providing any further help (AED+TM ). 3.2. Secondary outcome The proportion of volunteers who started BLS after defibrillation is presented in Fig. 3. This proportion ranged between AED groups from 93% (14 out of 15) to 33% (5 out of 15). The proportion of volunteers who started BLS after defibrillation in the AED groups, also differed significantly (P < 0.03). The results of the defibrillator “AccessTM ” are marked with an asterisk in Fig. 3 due to a procedural peculiarity of the training device. After completion of the first shock, the training simulation started again from the very beginning, shortly after its last prompt: “in absence of vital signs start cardio-pulmonary-resuscitation”. Therefore, investigators had to turn off the device after this prompt and ask lay helpers what they would do next. Once the device was turned off, 13 out of 15 lay responders stated, that they would start
Fig. 2. Defibrillator type and the time to first shock (seconds, mean and 95% CI). In three occasions with AED+TM and in one occasion with Fred easy® volunteers failed to deliver a shock.
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Fig. 3. The number of volunteers who started BLS after shock according to the defibrillator used in random order. ∗Access had limited comparability to other defibrillators, because the training-device had to be turned off after the last voice prompt.
BLS after the shocks. Hence, regarding the secondary end point, the “AccessTM ” AED cannot be compared to the other AEDs directly. 3.3. Influence of gender, age and time since last CPR training on the use of an AED There was no significant association between gender and time to first shock (P < 0.7) and the proportion of BLS started after the shocks (P < 0.41). There was also no significant association between the time since the last CPR training and time to first shock delivered (P < 0.69) or whether BLS was started after the shocks (P < 0.96). 3.4. Miscellaneous Findings Electrodes were not attached correctly in nine cases (4 Power HeartTM , 2 AED+TM , 2 AccessTM , 1 CR+TM ). Volunteers stated that they were confused about the electrode positioning in 14 cases (5 Power HeartTM , 3 AccessTM , 2 Fred easy®, 2 CR+TM , 1 AED+TM ) but placed the pads correctly. In two cases the lay rescuers did not remove the plastic liner from the pads (1 Power HeartTM , 1 AED+TM ). Two volunteers in the AED+ group did not remove clothing from the manikin’s chest before attaching the electrodes. The information button provided by the HS1TM was pressed by all users (15 out of 15) to be guided through BLS.
4. Discussion We could demonstrate clearly that there are significant differences between the AEDs tested, with regard to the time to first shock. These differences were not only statistically significant, but also of clinical significance. Looking at the time to first shock, the mean difference between the AEDs was as much as 50 s. This is of particular interest, because the time with the AED until the first shock is delivered is most likely time without chest compressions and therefore no-flow time [14]. Hence, this length of time could lead to increased mortality at the rate of almost 10% per minute [4]. Keeping this time to a minimum must be one of the major aims in developing AEDs. Recently, it was reported, that AEDs produced important delays in cardiac arrest situations [14,15]. It was beyond the scope of our study to identify prospectively the factors responsible for these important operational differences, but this heterogeneity should prompt further research. We also found significant heterogeneity in the proportion of BLS started after unsuccessful shocks. The maximum difference was as much as nine failures to start BLS in 15 trials. Theoretically, this could be translated into a relative risk reduction of 90%, when comparing the best and the worst AED, or a number needed to treat of two. Due to the importance of bystander BLS [6], a safe and easily understandable guide through the following steps after shock delivery is of utmost importance. Most volunteers in our experiment had attended CPR training before. This might be due to the fact that first aid
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education is mandatory when applying for a driving license in Austria. Former studies showed quite similar periods before the first shock was provided by untrained lay responders [12]. The large number of successfully simulated defibrillations also strengthens former findings of the simple use of AEDs in general, even by school children [11]. According to current knowledge neither helpers nor patients were endangered through the first aid efforts including defibrillation during our experiment [16]. Therefore, even untrained helpers are able to provide early defibrillation safely. We assumed that effects of the design had been extensively tested in advance for all AEDs by the respective companies. Given the simple aim of an AED to deliver appropriate shocks and guide BLS, it is indeed interesting that we could find differences in the operational outcome. It seems obvious, that the design of the device itself creates these differences. Most likely the key factors for failure were the content and volume of voice prompts and the arrangement of the buttons. We had the impression that some prompts were easier to understand for first time users, whereas others were not. In the absence of any correlation between the time since last first aid training and the initiation of BLS after shock, we conclude that volunteers placed a great deal of trust in the devices prompts. Once confused by a prompt, many of the volunteers stopped their BLS, despite former training. We could observe difficulties if voice prompts were given too quickly in a sequence. Our impression also was, that confusion could occur if the pictures were too numerous or too small. The scenario of our experiment was a semi-public place comparable to the environment of a shopping mall. Though not extreme, the presence of voices and light conditions from a big window seemed to have an effect on the operation of the AEDs. Therefore, it should be assessed if the devices could be used in bright or low light conditions. Also, loud and disturbing surroundings should not detract from the application and operation of an AED. 4.1. Limitations Even though AEDs and their user-friendliness turned out to vary in our experiment, the relevance for real cardiac arrest situations remains unclear. Volunteers knew about the simulated situation and in general showed very calm behaviour, which is unlikely to be the case in a real event. However, as AEDs have been used infrequently by lay-rescuers to date [17], it is currently not possible to gain necessary patient numbers to compare the effectiveness of different AEDs in clinical circumstances. Experimental work is probably the best we can have at the moment. We did not investigate if BLS was performed in an effective way after defibrillation. Possible advantages caused by special interactive voice prompts, for example as given by the AED+TM are therefore not reported in this trial.
Because of the absent impedance in the manikins, investigators had to push a button, to simulate the attached electrodes. Even though being aware of this problem, this procedure may have caused a minor delay. 4.2. Specific findings in the AEDs 4.2.1. LIFEPAK CRTTM (Medtronic, Minneapolis, USA) Users of the CR+TM defibrillated very quickly. The narrow 95% CI indicates, that many users were guided through the defibrillation process well. The flashing shock button was visible without problems in all light conditions. Voice prompts are given loud and clearly. The two clearly marked electrodes guided users to the correct electrode position. The device prompts the user to start BLS by using the abbreviation “BLS”, which is commonly unknown. This may be why only five out of 15 volunteer helpers started BLS after the initial defibrillation. Helpers reacted in a confused manner by pressing the shock button several times, turning the device off and on or by aborting their bystander support. 4.2.2. Fred easy® (Schiller AG, Baar, Switzerland) Pictures on the electrodes show the users how to attach the pads in a correct position. Lay helpers liked the advice to start BLS or to bring the patient in recovery position depended on the presence of vital signs. Voice prompts that were not understood could be read on a display in addition. The device did not start the ECG analysis on its own. Therefore, users were prompted to press the on/off button after attaching the pads. One user pushed the button until the device was turned off and no shock could be delivered. This was the only device where users had to push an analyse button ( = on/off button). In presence of a non shockable rhythm the device prompts users to start BLS by giving two breaths and compressing the chest 15 times if they were not able to detect vital signs. In the presence of vital signs the recovery position is recommended by the AED. 4.2.3. AED+TM (Zoll Medical, Chelmsford, Massachusetts, USA) The single electrode of the AED+ PLUSTM seems to prevent users from attaching the pads in an incorrect position. If performing the chest massage too weakly the AED+ gives feedback to press deeper. Also the frequency of the chest compressions is advised by a metronome. These feedback features were not tested during our experiment with the training device, therefore maybe existing advantages are not highlighted here. One user failed to open the AED. Another volunteer needed a lot of time to find out how to open the device. Once opened, one participant tried to position the top of the AED under the manikins head unsuccessfully and lost valuable time. It seemed that the device prompted users too quickly and that optical signs were only understood after feedback and training. Two users did not undress the manikin to attach the electrodes. As the volume of the prompting voice of the training unit was quite low, some users had dif-
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ficulties hearing the prompts clearly. The button to switch on the device was not visible enough for all users. 4.2.4. AccessTM (Access Cardio Systems, Concord, Massachusetts, USA) This device was the smallest of the devices tested. Electrode positioning is indicated on the electrode package clearly. Once the package is opened, the guiding pictures are not clearly visible any more. The device prompts users to plug in the electrodes by saying: “Connect electrodes”. This prompt was not understood by all users, some thought that they had to attach the electrodes at that point and were unsure how to do this. The pictures shown on the pads are quite small and were not clearly visible for all volunteers. Some volunteers had problems with opening the lid, because the mechanism is not shown clearly. As already mentioned, the particular training programme of this device produced a peculiar situation for the interpretation of the further BLS guidance by restarting after the first shock instead of continuing the regular algorithm (see above). 4.2.5. Power Heart training unitTM (Cardiac Science Inc., Irvine, California, USA) Opening the lid activates this AED. Because the voice prompts did not start immediately after activation, some users closed the lid again, to search for an activation button. The voice prompt to attach the electrodes was misunderstood by three users concerning the position. These volunteers attached the electrodes directly to the manikin’s mamillae because the AED prompts: “Attach the electrodes to the patient’s chest”. Voice volume was low and the LEDs of the “flashing” button were too weak in daylight conditions. One volunteer did not remove packing material from the electrodes. 4.2.6. HS1TM (Philips medical system, Andover, Seattle, USA) This device guides the user with slow and clear prompts. Users stated that the different signed electrodes of this device were useful. It also provides an information button to get further instruction as to how to start and provide BLS. All users pressed this button and did exactly what the device prompted. The recommended heart compression rate given by a metronome was appreciated by the volunteers. Mouth to mouth ventilation was explained precisely as well as chest compression.
5. Summary We could demonstrate that there are significant differences between AEDs, concerning important operational outcomes such as the time to first shock and start of BLS. It seems to be likely that the design of the device itself accounts mainly for these differences, but the proof for that was beyond the scope of this study. Factors for failure may
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have been related to the content and volume of voice prompts and arrangement of buttons. Further research and development is urgently required to optimise user-friendliness and operational outcomes.
Acknowledgements We are indebted to the training centre of the Vienna Red Cross, for kindly supplying us with the manikins and other training material as well as to Medtronic Austria, Chemomedica Vienna, Zoll Medical, Schiller Austria, Marquette Hellige, and Philips Medical Systems for providing us with the AEDs and the training electrodes.
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