The impact of response time reliability on CPR incidence and resuscitation success: a benchmark study from the German Resuscitation Registry

Sudden cardiac arrest is one of the most frequent causes of death in the world. In the United States and Europe, about 300,000 and 450,000 people, respectively, meet this fate [1, 2]. Males are affected markedly more frequently than females: The ratio is 4.1:2.7 [3]. In Germany, data derived from the World Health Organisation's MONICA registry (Multinational Monitoring of Trends and Determinants of Cardiovascular Disease) show a predicted incidence 123/100,000 inhabitants/year in the 35- to 64-year-old age group [4, 5], whereas in the European Union (EU), per 100,000 inhabitants, resuscitation attempts are performed to treat only about 55 patients [1, 6‐9]. Thus, in the EU, with about 500 million inhabitants, more than 275,000 resuscitation attempts are made annually. However, more than half of the patients in sudden cardiac arrest die without any resuscitation attempt because the event occurs unwitnessed or the emergency medical service (EMS) team, owing to statutory requirements, arrives too late at the patient's site and only can declare the patient's death. Out-of-hospital cardiopulmonary resuscitation (CPR) poses a huge challenge to emergency medical services because sudden cardiac death is a particularly time-critical event. Additionally, successful management requires a complex and target-oriented response of all acting persons and the entire chain of survival, from dispatch centre personnel to the hospital team.

To improve treatment, the International Liaison Committee on Resuscitation (ILCOR), or rather the European Resuscitation Council (ERC), publishes new resuscitation guidelines regularly every 5 years, with the latest one being released in October 2010 [10‐17]. To develop these guidelines, experts in various scientific fields screen and evaluate current studies, amongst which are studies concerning 'telephone-guided CPR' [18‐20], therapeutic hypothermia [21‐24] or vasopressin treatment [25‐27]. Following publication of the guidelines, it is essential to teach and subsequently implement them into EMS systems.

In highly qualified EMS systems, including well-trained emergency physicians, spontaneous circulation may be restored in up to 53% of patients at least until admission to hospital [1, 9, 28]. Discharge rates in these EMS systems are reported to be 14% to 20%, and 1-year survival rates can reach up to 12%. The 10-year survival rates of patients discharged from hospital may reach 46% [1, 9, 28, 29]. Compared with these highly qualified EMS systems, markedly lower success rates are observed in other EMS systems, with only 9% to 12% of patients being admitted to hospital and only 1% to 3% being discharged from hospital with good neurological outcomes [1, 8, 9, 28‐30].

These data clearly show that there are considerable differences between EMS systems concerning treatment success following cardiac arrest and resuscitation, although in all systems the current international guidelines for resuscitation are used [1, 6, 8, 9, 28]. It is therefore essential to analyse the reasons for these differences. However, few studies have been published correlating resuscitation results with known influencing factors such as response times, qualifications of team members, actions taken during resuscitation and quality management procedures.

Not least for this purpose, the German Society for Anaesthesiology and Intensive Care Medicine (Deutsche Gesellschaft für Anästhesiologie und Intensivmedizin (DGAI)) has set up the German Resuscitation Registry (GRR), which was officially implemented in 2007 [31, 32]. In this study, we investigated the impact of response time reliability (RTR) on CPR incidence and resuscitation success using return of spontaneous circulation (ROSC) after cardiac arrest (RACA) score and data from seven German EMS systems participating in the GRR.

This study demonstrates for the first time a relation between the RTR, CPR incidence and resuscitation success rate for sudden cardiac arrest in Germany (Tables 3 and 4 and Figures 1 and 2). Our study clearly shows that the EMS systems with the longest response intervals have the lowest CPR incidence and CPR success rates, calculated per 1/100,000 inhabitants/year.

It is noteworthy that the 'percentage ROSC rate' and the 'admission to hospital rate', which are usually used to compare EMS systems, did not differ between both groups and thus seem to be weak indicators of the performance of EMS systems (Figure 2). In addition, the RTR seems to be a particularly important influencing factor. On the one hand, it affects the frequency of resuscitation attempts by an EMS system; on the other hand, it affects the resuscitation success related to the population served. In this study, the time interval from when the call is received until the arrival of the first ambulance at the scene was used to calculate, consistently for all centres, the RTR in resuscitation missions. The rate of patients reached within 8 minutes of the call was determined. This time interval corresponds largely to the national standard for response times in the United Kingdom, whereas in Germany, owing to different state laws regarding EMS, there is no nationwide standard. According to the heterogeneous legal requirements, the best RTRs were found in the most densely populated areas (Bonn and Münster), with 90% of the patients reached by the first ambulance within 8 minutes after the call. It is remarkable that in the very rural EMS system of Marburg, which has the second lowest population density, 79.8% of the patients were reached within 8 minutes after the call. This success is explained by high number of EMS vehicles and unit-hours in Marburg. In contrast to the EMS system of Rendsburg-Eckernförde, which also provides service in a rural area, Marburg reached 108.3 unit-hours/km² service area, which is more than twice the provided unit-hours in Rendsburg-Eckernförde.

A high RTR regularly shortens the interval without treatment, so professional resuscitation attempts may be initiated earlier. In other regions, this leads to improved admission and survival rates as described by Hollenberg et al.[34], who compared the resuscitation success rates of Gothenburg and Stockholm (admission rates 30% vs 16%). Vukmir et al.[35] showed that more patients survive when it is possible to initiate resuscitation attempts within 8 minutes of the call or not (56 vs 32 patients). Our study supports the demand for a standardised response time interval for the arriving first vehicle and RTR > 70%, meaning that > 70% of the patients should regularly be reached within 8 minutes after the call.

Because regional state laws in Germany differ, response intervals are defined differently and healthcare funds provide financial means to reach only the respective standards. Thus, a German EMS system can realise a response interval standard only within a given legislative and financial framework. To compare the quality of EMS care under these conditions, further indicators must be considered. The survival rates following cardiac arrest are, in addition to other factors, influenced by techniques and quality of BLS [36, 37], ALS [38‐41] and postresuscitation care [30, 42‐44]. Therefore, in our study, the quality of EMS care was analysed by additionally assessing 'percentage survival rates', that is, ROSC and admission to hospital, of the total population and subgroups defined beforehand, as well as in comparison to a predictive value (RACA score) [33]. Table 4 shows that both groups of EMS systems could achieve higher ROSC rates than predicted by the RACA score, but did not differ regarding the 'percentage survival rates'. This means that (1) all seven EMS centres studies belong to the the best performing systems in the GRR, and (2) a lower CPR incidence does not lead to a positive selection of 'good risks'. The first statement is additionally supported by a comparison with the admission rates from the GRR, because all seven centres performed better than the other centres participating in the GRR, with, on average, 42.8% vs 32.7% of patients being admitted to hospital.

There might be various reasons for the superior resuscitation results of the seven participating EMS systems that we studied. It is well-known that both a collapse in public and a witnessed collapse improve the chances of surviving an OHCA [9]. However, in this respect, there were no differences between the seven centres participating in our study and the total GRR participants (witnessed = 60.2% vs 61.6%, collapse in public = 18.3% vs 18.2%). The results cannot be explained by the rates of bystander CPR, which were 18.8% in the seven participating centres in our study and 18.5% in the total GRR. It is remarkable that in Germany bystanders too rarely initiate CPR before EMS arrival, even when they witness the collapse. The positive influence of bystander CPR on survival rate has been demonstrated frequently [45‐47]. Previous studies have shown similar setups in German and European systems [9, 48]. One reason for the low rate of bystander CPR in Germany may be that > 70% of the events occur at home and that it is usually elderly people who are affected and live alone or with an elderly partner who is unable to perform BLS spontaneously. As a consequence, the approach of telephone-guided CPR should urgently be intensified in the EMS systems that we studied and in Germany generally.

The comparatively high survival rates in the seven analysed centres in our study may be explained by the higher rate of patients found in a shockable rhythm (rate of VF/VT = 28.4% vs 23.1% in the entire GRR; P < 0.001). Therapeutic hypothermia following ROSC was induced in 46.2% of the patients in the seven centres in our study, but only in 13.7% of all patients in the GRR (P < 0.001).

Special efforts are made in all seven centres studied regarding CPR training in general, particularly BLS CPR. This is reflected by the fact that, in three centres, intensive training is provided in the use of special supportive devices, which are used extensively. Bonn has established LDB CPR use [37, 49], ACD-CPR is applied in connection with an impedance valve in Göppingen [50] and, after intensive training and continuous scientific evaluation, a CPR feedback system is regularly used in Münster [51, 52]. In this study, we found no evidence that using these mechanical or feedback devices increases CPR success. However, as the data derived from the remaining participating centres show, excellent results are possible by applying only committed manual CPR.

The results of this study demonstrate that, with regard to the level of EMS systems, the faster ones more often initiate CPR and increase the number of patients admitted to hospital alive. Furthermore, we have shown that with the use of very different approaches, all EMS systems that adhere to and provide intensive training based on the 2005 ERC guidelines, superior and, on the basis of international comparisons, excellent success rates following resuscitation can be achieved. The data derived from the three EMS systems in our study (Göppingen, Gütersloh and Marburg) in which the discharge rates based on 1/100,000 inhabitants/year could be calculated, with results between 8.0 and 10.7/100,000 inhabitants/year, take a top position in Europe (Table 3). Despite these internationally compared excellent results, some potential improvements could be identified for the centres. (1) Change of location of ambulance and emergency physician's stations, implementation of global positioning systems (GPSs) and computer-aided dispatch systems should be used to improve the rate of calls reached within the standardised response time interval. (2) The time interval between EMS arrival and onset of CPR should be shortened. (3) Intensive, required training in BLS should be implemented, especially when mechanical devices are used. (4) Special CPR training for elderly citizens should be required. (5) Awareness should be raised among, and training should be provided to, the general population regarding the importance of bystander CPR. (6) A structured interview of emergency calls and telephone-guided CPR instructions by the dispatch centre should be implemented. (7) Consistent use of a standard operating procedure concerning treatment of hypothermia, starting in the preclinical phase, should be implemented.