Advanced airways include supraglottic airways, laryngeal mask airways, or endotracheal (ET) tubes. These airways should be initiated only by trained personnel as soon as available since they provide ventilation for any age. 

If these advanced airways are not available, rescuers continue to use mouth-to-mouth, mouth-to-mask, or a bag-mask for breathing in an arrest situation. If an advanced airway is in place, the compression to breath ratio should be as explained below.

If a mask or advanced airway is not available, rescuers should be ready to provide mouth-to-mouth rescue breathing during CPR. They should be careful to avoid over-ventilation, which can fill the stomach with air and prevent proper lung expansion.