because prolonged breaths increase the duration of positive intrathoracic pressure. Keeping artificial ventilation rates low is difficult because the high-adrenaline state of the rescuer alters time perception, and the rapidly refilling
bag ventilation systems set up a reflex in which rescuers are
inclined to deliver breaths as soon as the bag inflates. Because
even focused reduction did not ensure compliance with the
guidelines, the use of adjunct devices that indicate when 6 to 7.5
seconds have elapsed (for delivery of 8 to 10 breaths per minute)
should be encouraged