An adaptor (10) is used to convert an oxygen face mask (50) for capnography. The adaptor (10) comprises a body (12) with a first connector (14), a second connector (16) and a passageway (18) extending therebetween. The first connector (14) is configured to engage a respiratory gas (C02) monitoring line (not shown). The second connector (16) has a substantially tapering profile, with its cross-section decreasing with increasing distance from the first connector (14). The substantially tapering profile of the second connector (16) is made up of a plurality of annular ribs (24), separated by annular grooves (26), forming a graduated or stepped configuration. Such a configuration is helpful for securely engaging any one of a number of apertures of different sizes when converting the oxygen face mask (50) for capnography.
