There have been several changes made over the past few years to the guidelines for advanced life support and, to a lesser degree, basic life support (BLS).

The current guidelines advocate 30 chest compressions to every two rescue breaths (previously this was 15 to two). Performing mouth-to-mouth ventilation tends to discourage people from performing BLS. It also takes time, is technically difficult and probably has a detrimental physiological effect in the setting of cardiac arrest. A new prospective, observational study investigated exactly how useful rescue breaths are in an out-of-hospital cardiac arrest.

The study investigated 4,068 adult patients with witnessed out-of-hospital cardiac arrest. On arrival at the scene paramedics assessed the BLS (if any) that had been provided. Three groups were identified: cases where no resuscitation was attempted (2,917, 72 per cent), where conventional CPR (chest compressions and rescue breaths) was applied (712, 18 per cent) or where chest compressions alone were given (439, 11 per cent). The primary outcome measure was a favourable neurological outcome 30 days after cardiac arrest. Subgroups were also defined to identify differences in those with apnoea, shockable rhythms and resuscitation started within four minutes of arrest.

Not surprisingly, patients who received some form of bystander resuscitation did significantly better than those who were left until the paramedics arrived. However, the numbers achieving the primary outcome were low, with 5 per cent in the bystander resuscitation groups compared with 2.2 per cent in the no resuscitation group.

There was no significant difference in the primary outcome between the chest compression-only group and the conventional CPR group. Furthermore, patients in all three subgroups who only received chest compression fared significantly better than those who received conventional CPR.

It is always difficult to gather robust, evidence-based data in the setting of pre-hospital emergency care, but this study makes interesting reading and could provide food for thought for the next revisions to the resuscitation guidelines.