When heart attacks occur out of a hospital setting, members of the public often step in to provide cardiopulmonary resuscitation (CPR). These bystanders are often advised by the emergency medical services (dispatchers) on how to proceed while waiting for an ambulance to arrive. A study published Online First (www.thelancet.com) and in an upcoming Lancet says that dispatcher-assisted CPR produces better results when it involves chest compression only, rather than the standard protocol of chest compression and mouth-to-mouth ventilation. The Article is by Dr Peter Nagele, Washington University School of Medicine, St Louis, MO, USA and Medical University of Vienna, Austria, and Drs Michael Hüpfl and Harald F Selig, also of the Medical University of Vienna.
The authors systematically reviewed existing evidence regarding chest-compression-only CPR and compared the findings with standard CPR in a meta-analysis. In the primary meta-analysis, they included trials in which patients were randomly allocated to receive one of the two CPR techniques, according to dispatcher instructions; and in the secondary meta-analysis, they included observational cohort studies of CPR. All studies had to supply survival data. The primary outcome was survival to hospital discharge.
The results of the primary meta-analysis—that pooled data from three randomised trials involving over 3,000 patients—showed that chest-compression-only CPR was associated with improved chance of survival compared with standard CPR (14 % vs 12%, with the relative chances of survival increased 22% by chest-compression only CPR). The absolute increase in survival was 2•4%. Put another way, one life would be saved for every 41 patients treated with the new chest-compression only method.
In the secondary meta-analysis of seven observational cohort studies (but no randomised trials), no difference was recorded between the two CPR techniques, with both groups recording survival rates of 8%. However this second group of studies did not cover dispatcher-assisted CPR; rather they were based on bystanders who had decided on their own whether to do chest-compression only CPR or chest-compression plus mouth-to-mouth.
The authors note that in the primary meta-analysis, none of the three trials involved on its own showed a statistically significant difference in the two techniques, probably due to insufficient statistical power. The three had to be combined for the results to gain statistical significance. The authors say: "The fact that only three randomised trials have been done is testament to the difficulties associated with well designed prospective studies in this setting, such as obtaining of informed consent*, the little time available to randomise patients, adherence to the study protocol, tracking of patients and outcomes, and masking of investigators, study personnel, and patients from the allocated intervention. Because survival rates after out-of-hospital cardiac arrest are low and large treatment effects are unlikely, very large sample sizes are needed to show a significant survival benefit."
The authors say that that continuous, uninterrupted chest compressions are vital for successful CPR. They say: "By avoidance of rescue ventilations (mouth-to-mouth) during CPR, which are often fairly time-consuming for lay bystanders, a continuous uninterrupted coronary perfusion pressure is maintained, which increases the probability of a successful outcome."
They add that provision of oxygenation and ventilation during the first minutes after cardiac arrest may not be as important as successful chest compression in the moments immediately following a cardiac arrest. This is because when the heart stops following a heart attack, there should be enough oxygen in a person's system to keep them alive. As such, chest-only CPR is easier to teach than that involving mouth-to-mouth, increasing the chances of a bystander being prepared to carry out CPR.
They conclude: "Our findings support the idea that emergency medical services dispatch should instruct bystanders to focus on chest-compression-only CPR in adults with out-of-hospital cardiac arrest." They add that further research is now needed into whether unassisted and dispatcher-assisted bystander chest-compression-only CPR provide similar survival benefits.
In a linked Comment, Dr Jerry P Nolan, Royal United Hospital NHS Trust, Bath, UK, and Dr Jasmeet Soar, Southmead Hospital, North Bristol NHS Trust, Bristol, UK, say: "How should the results of these meta-analyses affect practice? If the information from a caller suggests sudden adult cardiac arrest, the dispatcher should provide instructions assertively on compression-only CPR. Thus the 'kiss of life' should be replaced by 'Keep It Simple, Stupid', which is broadly consistent with the practice of many emergency medical dispatchers in the UK. For adult primary cardiac arrest, dispatchers instruct the bystander to give 600 compressions (about 6 min) followed by two rescue breaths and then a compression:ventilation ratio of 100:2 until emergency medical personnel arrive**. The general role of bystander compression-only CPR is less clear. A bystander who starts CPR will not know how long the emergency medical services will take to arrive, and will not understand the difference between asphyxial and primary cardiac arrest. Therefore, ideally, lay people should continue to be trained in standard CPR. But any CPR is better than no CPR. Compression-only CPR has an important role in increasing the rate of bystander CPR by those who are untrained, who have only a minimum time for training, or who are unwilling or unable to provide rescue breathing."
In addition to his Comment, Dr Nolan adds that new CPR guidelines will be published by the Resuscitation Council (UK) on Monday, October 18. (www.resus.org.uk).
Peter Nagele, Medical University of Vienna, Austria and Washington University School of Medicine, St Louis, MO, USA. T) +1-314-362-5129 E) nagelep@wustl.edu
Dr Selig T)+43-676-9492220 E) harald.se@gmx.at
Dr Hüpfl E) michael.huepfl@meduniwien.ac.at
Dr Jerry P Nolan, Royal United Hospital NHS Trust, Bath, UK. T) +44 (0) 7768 595911 E) jerry.nolan@nhs.net
For full Article and Comment, see: http://press.thelancet.com/cpr.pdf
Note to editors: * usually there is a waiver of informed consent; other prehospital studies require consenting of next of kin or family members
**Barron T, International Academies of Emergency Dispatch, Bristol, UK, personal communication
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Journal
The Lancet