The new 2010 ERC life support guidelines stress the importance of high quality chest compressions for effective BLS, and advise that they are performed to a greater depth and within a narrower range than recommended by their 2005 predecessor [11, 12].
The importance of maintaining a compression rate above 100 min-1 is emphasised within the new guidelines but the upper limit of 120 min-1 remains. Despite this, the rate of chest compression delivery was too fast in a significantly increased fraction of rescuers trained with the 2010, rather than 2005, guidelines. No significant difference in rescuers’ ability to perform any of the other tested skills without error is incurred with use of the new guidelines.
A significantly greater proportion of lay-rescuers trained with the new ERC guidelines performed at least one skill erroneously when demonstrating BLS. The overall increase seen in lay-rescuers performing BLS erroneously therefore appears to be directly related to rescuers completing chest compressions at too fast a rate due to an inability to meet the narrower confines for rate recommended by the new ERC guidelines.
This may result from course teachers emphasising the need to perform chest compressions at a relatively faster rate that does not fall to the lower limit of 80–99 compressions minute-1 that was permitted by previous guidelines. In addition, the need to perform chest compressions at a greater depth may instil within CPR providers a mentality of ‘harder and faster’, through which the more energetic pursuit of greater chest compression depth results in a faster rate.
In order to explore this latter point, further research is required to determine whether lay providers are able to skilfully and effectively dissociate deep chest compressions from a tightly controlled rate of chest compression delivery. In addition, basic life support course directors and instructors should be reminded to focus training for providers towards delivering chest compressions at the depth required by the 2010 guidelines, whilst within a controlled rate (with the use of a metronome, for instance, rather than adopting and disseminating a ‘harder and faster’ mentality towards the new ERC guidelines).
The effect of providers seemingly adopting this mentality is, however, unclear. There exists a strong positive correlation between the number of chest compressions delivered to a casualty each minute and the likelihood of successful outcome . However, although faster chest compressions are thought to improve prognosis by generating greater blood flow to the brain and myocardium, animal studies have indicated that cardiac output reaches a plateau between 60 to 120 compressions per minute [17–19].
At rates of greater than 120 compressions per minute, available time for both diastolic myocardial perfusion and adequate venous return decreases [17–19], thereby potentially limiting coronary perfusion rates and decreasing cardiac output. Furthermore, fatigue occurs earlier, with greater impact on CPR quality, if the number of chest compressions delivered by lay-rescuers is increased . Lay rescuers are unable to meet the narrower range for chest compression rate recommended within the new 2010 ERC life support guidelines in our study. Their resultant tendency to complete chest compressions at rates greater than 120 compressions per minute may therefore decrease the likelihood of successful CPR following cardiac arrest through reduced blood flow to vital organs and increased rescuer fatigue.
It is, however, difficult to detail precisely the potential clinical impact of our findings. For example, this study is limited in its inability to specify the degree to which chest compression rate exceeded the recommended upper maximum. In addition, rescuers using the 2005 and the 2010 guidelines performed all other assessed skills without significant apparent variation in error rates. Lay rescuers were therefore seemingly able to perform compressions at the greater depth required by the new guidelines as successfully as those meeting a shallower depth in the old guidelines. This measurement was subjective, however, and assessors’ appraisal of the depth of trainees’ chest compressions may have been inaccurate as a result. Nevertheless, the effect of deeper chest compressions performed at too fast a rate is not fully known and may require elucidation, particularly if future studies confirm the objective data outlined within this report.
Despite these limitations, the peer-led course from which the data for this study is sourced has run successfully for over 15 years and is of high repute. Instructors are trained to meet international standards, and deliver teaching in accordance with recommendations from the ERC and to the same standard as external faculty . For the periods from which the data included in this study is taken, teaching standards were rigorously reviewed by the same experienced external faculty members for similar periods of time. Therefore, although we acknowledge that our instructors are not under constant supervision, teaching quality is unlikely to have varied within or between courses due to the measures taken in order to ensure standardisation.
End of course assessments on which this study was based were carried out similarly for prospective rescuers using the 2005 and 2010 guidelines. Senior students assessed candidates using set written criteria (which varied only to reflect changes in ERC guidelines, as shown in Additional file 1: Figure S1) and were moderated by external faculty. We have previously shown that agreement between external faculty and student observers is high and do not envisage that the results of this study were affected by the nature of candidates’ assessment .