A recent meta-analysis of 79 studies involving 142 740 patients with out-of-hospital cardiac arrest of presumed cardiac aetiology documented a survival-to-hospital discharge rate of 7.6% (95% CI 6.7–8.4) . This analysis showed that survival from out-of-hospital cardiac arrest has changed little over the last 30 years, although a few recent studies report improving survival rates [2, 3]. Bystander cardiopulmonary resuscitation (CPR) increases the chances of long-term survival after out-of-hospital cardiac arrest [1, 4] but bystander CPR rates are low: in England in 2004–2006 the bystander CPR rate was 36% (unpublished data, National Out-of-Hospital Cardiac Arrest Project), which is consistent with the 32% documented in the recent international meta-analysis . Reasons for bystanders’ not attempting CPR include: no previous training ; panic; concern about causing harm; and unwillingness to perform mouth-to-mouth ventilation (rescue breathing) .
Is ventilation of the lungs absolutely necessary during CPR? Intuitively, the provision of oxygen, even if in the form of expired air (approximately 17% oxygen) ought to be essential if full neurological recovery is to be achieved after anything but a very brief period of cardiac arrest. Yet many animal studies of cardiac arrest have shown either no difference in survival  or reduced survival [8, 9] with the addition of ventilation to chest compressions. A limitation of these studies is that, in contrast to humans, the airways of the animals are generally patent when supine, which may enable chest compressions alone to generate some ventilation. In animal studies, frequent gasping occurs during good quality CPR and this provides significant ventilation . Gasping is also common after cardiac arrest in humans but it decreases rapidly with time. Only 7.1% of patients with out-of-hospital cardiac arrest were noted to be gasping on arrival of emergency medical services (EMS) personnel in Japan , but in another study, gasping was present in 39 of 119 (33%) cardiac arrests that were witnessed by EMS personnel . When the EMS arrival time was more than 9 min after cardiac arrest, gasping was present in just 25 of 338 (7%) patients . Not surprisingly, gasping is associated with survival . Animal models that incorporate an obstructed airway [14, 15] or paralysis of the animals  may better reflect the clinical situation: they show worse outcomes with compression-only CPR – in these studies arterial oxygenation decreased substantially with compression-only CPR. If airway patency is maintained, do chest compressions generate adequate ventilation in human cardiac arrest? A study of 17 patients in an emergency department who were undergoing chest compressions using a mechanical compression device (Lund University Cardiopulmonary Assist System – LUCAS), their tracheas intubated, documented a median tidal volume per compression of just 42 ml – considerably less than the dead space . These patients had been in cardiac arrest for more than 40 min, which implies that their lung compliance was probably poor (lung compliance decreases with prolonged CPR). Almost five decades ago, Peter Safar  showed that following failed prolonged attempts at CPR, chest compressions alone produced zero ventilation in 10 out of 12 patients with intubated tracheas. To my knowledge, there are no human data on tidal volumes produced with chest compressions immediately after the onset of cardiac arrest, but high-quality compressions may prolong gasping, probably adding significantly to any ventilation achieved with compressions alone.
Aside from the reluctance by laypeople and healthcare professionals to provide mouth-to-mouth ventilation [19–21], the latter has other disadvantages. Mouth-to-mouth ventilation is associated with a significantly increased risk of regurgitation compared with no CPR or compression-only CPR . The time taken to attempt two rescue breaths, which may be as long as 14–16 s [23, 24], represents a significant interruption to chest compressions and contributes to the ‘no-flow’ time. In comparison with conventional CPR, compression-only CPR is easier to learn . In a study of dispatch-assisted CPR (the caller is given instructions by the ambulance controller on how to do CPR), full instructions were more likely to be delivered completely when the ventilation component was omitted and survival was non-significantly higher in the compression-only group .
There are no prospective randomised trials comparing compression-only CPR with conventional CPR. However, eight observational studies have showed similar survival rates when bystanders delivered compression-only CPR instead of conventional CPR, and all showed that survival to hospital discharge was higher with compression-only CPR compared with no CPR [11, 27–33]. The methodology in all these studies was similar: on arrival at the scene, EMS personnel observed and documented the technique of bystander resuscitation (none, compression-only, or conventional CPR). Although compression-only CPR was not associated with statistically higher survival rates overall compared with conventional CPR, one of the studies documented subgroups in which the outcome was significantly better for the compression-only group, for example response times less than 4 min and shockable rhythms . The interpretation of observational studies such as these is fraught with difficulties because of the strong possibility of undetected confounders. Despite this, there has been a strong plea from some experts for compression-only CPR to be incorporated into international guidelines [34, 35] and the American Heart Association has published an advisory statement on ‘hands-only’ CPR – this advocates compression-only CPR if the bystander is not trained in CPR or is not confident in the ability to provide high-quality conventional CPR with minimal interruptions for rescue breaths .
Should we stop teaching rescue breathing to laypeople, and instead teach them to perform compression-only CPR? The strongest reason to adopt this approach is that it ought to (although we have no proof) increase the chance of a bystander’s providing CPR – we know that ‘any CPR is better than no CPR’. This strategy should produce at least equivalent outcomes (compared with conventional CPR) for those patients in cardiac arrest from a cardiac cause and where EMS response times are short. Approximately 58% (Japan)  to 80% (Scotland)  of out-of-hospital EMS-treated cardiac arrests are of primary cardiac aetiology. Those with asphyxial cardiac arrests (e.g. children or drowning victims), or where response times are long, are likely to need early ventilation if they are to have any chance of surviving. The findings of a recent observational study (using the methodology described above) of outcome among children in Japan with out-of-hospital cardiac arrest impact significantly on the compression-only CPR debate . Of 5170 paediatric (aged 17 years and younger) out-of-hospital cardiac arrests in Japan from 2005 to 2007, 71% were from non-cardiac causes. Within this subgroup, conventional CPR produced more favourable neurological outcome than did compression-only CPR (7.2% (45/624) vs 1.6% (1/380); odds ratio 5.54 (95% CI 2.52–16.99)). Among those children who had arrests from cardiac causes, favourable neurological outcome did not differ between conventional and compression-only CPR (9.9% (28/282) vs 8.9% (14/158), respectively; odds ratio 1.20 (95% CI 0.55–2.66)).
New cardiopulmonary resuscitation guidelines will be published in October 2010; what should be advised in relation to CPR by laypeople? The 2005 International Consensus on CPR Science already includes the recommendation that: ‘Rescuers should be encouraged to do compression-only CPR if they are unwilling to do airway and breathing manoeuvres or if they are not trained in CPR or are uncertain how to do CPR’ . This message is consistent with the advisory statement that was published later by the American Heart Association  and remains reasonable in the face of data published since then. This stance should encourage bystanders at least to attempt some CPR. More controversial is the suggestion that laypeople should be taught to provide compression-only CPR in preference to conventional CPR for witnessed, sudden collapse (even if they have been trained in conventional CPR) ; all the available data indicate that this is likely to be beneficial only if the EMS response times are short (4 min or less). If we want laypeople to provide conventional CPR for victims of asphyxial cardiac arrest (including most children), it implies that everyone still needs to be trained to provide mouth-to-mouth ventilation, which takes us back to where we are now. Handley has described a solution that would, at a minimum, get everyone trained to do compression-only CPR, while encouraging as many as possible to learn conventional CPR as well . In this very sensible, staged approach, compression-only CPR is taught to the whole community; the training would be simple and brief and, with the use of a variety of media, could even be self-directed. Those completing this training could then be encouraged to attend ‘follow-up training’ where they would be taught conventional CPR. Those with a duty of care, for example lifeguards and healthcare professionals, should continue to be trained in conventional CPR. Whether or not this strategy is adopted in the 2010 European Resuscitation Council and Resuscitation Council (UK) Guidelines will be made known later this year.