A hand-held apparatus that delivers pressurized breathing gas to the airway of a patient, thereby creating positive end expiratory pressure (PEEP) and reducing respiratory muscle fatigue. The apparatus includes a deformable reservoir, a breathing interface, and a pressure relief valve. The apparatus may include a means for creating fluid communication between the deformable reservoir and a source of pressurized breathing gas. The apparatus may also include an adjuster that allows a user to vary the pressure of the breathing gas contained in the deformable reservoir.