This disclosure describes systems and methods for ventilating a patient with a system that includes an accumulator for storing a gas mixture. The disclosure describes systems and methods for ventilating a patient with a system that includes an accumulator located away from the flow path that reduces or eliminates pockets or burps of an undesirable gas mixture from entering the gas flow path and reaching the patient after a gas mixture change. The disclosure also describes a novel approach for reducing or eliminating these air pockets of undesirable gas by utilizing a dip-tube.