A light-weight, portable mask connects to a portable capnography device for monitoring carbon dioxide in expiratory gas. The mask includes an enclosure that fits over the mouth and nose of a patient, and a single outlet to which an expiration lumen is attached. The expiration lumen is configured to attach to the portable capnography device. The expiration lumen and the capnography device are in a position that is parallel to the patient's face when the mask is in use. The portable capnography device is smaller than the mask. The mask may also include a one-way inhalation inlet vent that allows atmospheric air to enter the enclosure when the patient inhales. In this manner, an apparatus including the mask and the capnography device is used to monitor the breathing of a non-intubated patient, and is not configured to supply oxygen to the patient.
