Animal models show that arterial blood is completely desatu rated in <2 minutes of chest compression without ventilation, and therefore at least some air exchange is necessary to oxygenate blood.82 Recently published guidelines advocate delivering a slower ventilatory rate of 8 to 10 breaths per minute.76 Even slower rates may be optimal, and ongoing experiments will clarify the necessary ventilation rate in states of low blood flow. Furthermore, breaths should be delivered quickly, over approx-imately 1 second, because prolonged breaths increase the dura¬
tion 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 reeducation 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.
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