Extensive recent human data have indicated that ventilation during CPR is usually overzealous. Both emergency medical personnel and in-hospital resuscitation teams have been shown to deliver artificial breaths at rates far exceeding the published recommendations of the time (12 to 15 breaths per minute), averaging 20 to 30 breaths per minute.77,78 Despite retraining efforts, ventilation remained excessive with rates that, although slower, still exceeded guidelines, with an observed increase in breath duration as well.77 Positive pressure in the thoracic cavity hinders circulation by decreasing venous return, increasing intracranial pressure, and decreasing coronary perfusion pres¬sure, a critical predictor of return of spontaneous circulation.79,80 In animals, hyperventilation during 4 minutes of resuscitation reduced absolute survival by 70%.77 Furthermore, before a secure airway is obtained, breathing efforts interrupt chest compression, and 2 breaths take the average lay rescuer >15 seconds (stopping circulation for at least 25% of each minute).79 In an intriguing randomized trial of CPR technique, Seattle's 911 telephone staff randomly instructed bystanders to perform both ventilation and chest compressions versus performing chest compressions alone. Both groups had similar outcomes, with a trend toward higher survival to hospital discharge in patients assigned to the latter.81 The apparent benefit of withholding artificial respiration in this trial was likely the exclusive consequence of maintaining uninterrupted circulation because the human unconscious airway is often obstructed, and chest compressions do not provide any meaningful airflow.70