Hi, Actually, the volume guarantee does just affect ventilation, which means CO2 elimination. The tidal volume in HFOV is completely different from the conventional ventilations tidal volume which means how much the lungs should be inflated. To prevent from atelectasis, it is most important to keep adequate mean airway pressure. It is very much up to the Dead Space if you keep normal ventilation to those tiny bebis. I have never used MAP less than 9 cm because of trends of atelectasis, especially due to the small diameter of the ETT.