A blower module (28) for a ventilator (50) is disclosed. The blower module (28) comprises an impeller (3) mounted within a stator housing (11) on a rotatable shaft (7), the rotatable shaft (7) defining an axis of rotation (12) of the impeller (3). The housing (11) has a central gas inlet (13) substantially coaxial to the axis of rotation (12), and a substantially annular compression chamber (14) coaxial to the axis of rotation (12), wherein the compression chamber (14) has an annular gas inlet (16) and a gas outlet (17). The impeller (3) is arranged for directing a gas mixture from the central gas inlet (13) of the housing (11) into the annular gas inlet (16) of the compression chamber (14). The annular compression chamber (14) is bounded by a circular outer wall (19). At least part of the circular outer wall (19) is uninterrupted by the gas outlet (17).
