The invention relates to a breathing assistance device (1) comprising: - a firstgas inlet (5) for receiving a primary respiratory gas and a first regulating meansfor regulating said primary respiratory gas, both being located in a centralunit (2) - a second gas inlet (6) for receiving a secondary respiratory gas anda second regulating means (7) for regulating said secondary respiratory gas- a controlling means for controlling said first and second regulating meansin order to mix said primary and secondary respiratory gases in controlled respectiveproportions into a controlled mix of gases - a feeding means (4) for feeding apatient with said controlled mix of gases, characterised in that said secondgas inlet (5) and second regulating means (7) are both located in a secondary unit(8) removably connected to the central unit (2).
