Abstract: To ensure that the inner cannula is mated to the outer cannula of a tracheostomy tube, a pressure adjusting device is provided to the collar of the inner cannula so as to apply a biasing force against the tabs that extend from the hub of the outer cannula. The torque force that is required to assemble/disassemble the inner cannula to/from the outer cannula may be adjusted by increasing or decreasing the thickness of the pressure adjusting device which may be in the form of a spring ring which elasticity is adjustable by varying the thickness thereof. Ramps are provided within the collar of the inner cannula to guide the movement of the tabs relative to that of the collar. In addition, stops are provided within the collar for arresting any further movement of the tabs with respect to the collar. Indents are further provided within the collar whereat the tabs can rest.