An HME has exchange elements (4) at opposite ends of a tubular housing (1, 101) and a central port (2) for connection to a tracheal tube (3). An oxygen port (5, 105, 105′) is located centrally with the major part of it being contained within a recess (40, 140, 140′) on the exterior of the housing and extending at right angles to the length of the housing. The oxygen port (5, 105, 105′) opens into a wider passage (32, 32′) extending within the housing, which opens on the external face (30) of the two exchange elements (4). A large suction aperture (60) aligns with the port (2) opening to the tracheal tube (3) and is covered by a hinged flap (61) when not in use.