The question of how to respond to out of hospital cardiac arrest (OHCA) encapsulates the tension between the individual and the population perspective on health. Faced with someone who has just collapsed with no pulse, the appropriate response is clear. Cardiopulmonary resuscitation (CPR) makes it possible to sustain some individuals until their cardiac rhythm can be diagnosed; those found to have ventricular fibrillation can often be shocked back into sinus rhythm and evacuated to hospital, from which they have an over 70% probability, in the best centres, of being discharged alive.1

The question of what to do, at a population level, to enhance the number of people who survive is more difficult. For almost two decades it has been argued that what is needed is a coordinated “chain of survival”,2 which would include rapid access to skilled care, early CPR and defibrillation. What was initially less clear was how such a system could be put in place. The solution was largely seen as getting more defibrillators into trained hands. In some places the hands were those of physicians,3 while in others they belonged to paramedics.4 Much of the debate about who could take on this role centred around the accuracy of diagnosis; clearly it was undesirable to administer high voltage shocks to people who did not need them. Yet, whichever option had been adopted, there would never have been enough trained health workers to ensure that one would be readily available when he or she was needed.

The development …