When the heart stops pumping during cardiac arrest, cardiopulmonary resuscitation (CPR) is used to continue pushing blood and providing oxygen to vital organs. CPR involves a combination of chest compressions (to push the blood) and ventilations (to provide oxygen and gas exchange). There is a lot of research that has helped to optimize the provision of chest compressions, however there is considerably less research available to guide ventilations. The current guideline recommendations are based on limited data, and no data that is specific to cardiac arrest patients. There is a recognized need for research to better guide ventilation during CPR. This research will help to better define appropriate ventilation targets for cardiac arrest patients.