To Breathe or Not to Breathe.

The publication of the National Academy of Sciences scientific statement on cardiopulmonary resuscitation (CPR) in 1966 was a pivotal moment in the modern era of cardiac arrest care.1 This scientific statement recommended that CPR should consist of both exhaled air ventilations and chest compressions, and that is how standard CPR (S-CPR) was taught and performed for the next halfcentury. In 1997, the American Heart Association first revisited the role of rescue breathing during CPR on the basis of emerging laboratory and clinical research demonstrating the efficacy of chest compressions alone during cardiac arrest.2 However, at that time, there was inadequate evidence to make specific recommendations. In 2000, the American Heart Association first recommended compression-only CPR (CO-CPR) in circumstances when rescuers were unwilling or unable to perform mouth-to-mouth rescue breathing or for dispatcher-assisted CPR instruction.3 Over the subsequent years, a growing body of evidence emerged to support the efficacy of CO-CPR and its positive impact on bystander CPR rates, resulting in significant evolution of American Heart Association and other international CPR guidelines. The most recent 2017 American Heart Association and Emergency Cardiovascular Care Science focused update on basic life support for adult out-of-hospital cardiac arrest recommends CO-CPR for untrained rescuers and those trained in COCPR.4 When dispatcher instruction is needed, it is recommended that dispatchers provide CO-CPR instructions. However, when a lay rescuer is trained in CPR with chest compressions and rescue breaths, the guidelines now state that it is reasonable to provide rescue breaths in addition to chest compressions. The weakened recommendation on rescue breaths was based on persistent uncertainty about the relative efficacy of S-CPR versus CO-CPR for adults in cardiac arrest when delivered by lay providers. However, for infants and children in cardiac arrest, CPR with chest compressions and rescue breaths continues to be recommended unless bystanders are unwilling or unable to deliver rescue breaths.5 This recommendation is based on the fact that a majority of pediatric cardiac arrests have an asphyxial cause, as suggested by a subset of observational clinical studies.6–9 In this issue of Circulation, Riva et al10 describe the changes in the frequency and type of bystander CPR performed for all bystander-witnessed out-of-hospital cardiac arrests reported to the Swedish Register for Cardiopulmonary Resuscitation from 2000 to 2017. They also analyzed the independent associations between CPR technique and 30-day survival. A number of key observations are reported that support current guidelines, generate new hypotheses for future research, and highlight persistent disparities. Of greatest significance is the increase in bystander CPR frequency from 40.8% to 68.3% during the study period, which was © 2019 American Heart Association, Inc.