Non-rebreather mask

A non-rebreather mask, or NRB, is a device used in medical emergencies that require oxygen therapy. An NRB requires that the patient can breathe unassisted, but unlike a nasal cannula, the NRB allows for the delivery of higher concentrations of oxygen.

Design
The non-rebreather mask covers both the nose and mouth of the patient and attaches with the use of an elastic cord around the patient's head. The NRB has an attached reservoir bag, typically 1.5 liters, that connects to an external oxygen tank. Before an NRB is placed on the patient, the reservoir bag is inflated to greater than two-thirds full of oxygen, at a rate of 8–15 liters per minute (lpm). Approximately ¹⁄₃ of the air from the reservoir is depleted as the patient inhales, and it is then replaced by the flow from the O2 supply. If the bag becomes completely deflated, the patient will no longer have a source of air to breathe.

Exhaled air is directed through a one-way valve in the mask, which prevents the inhalation of room air and the re-inhalation of exhaled air. The valve, along with a sufficient seal around the patient's nose and mouth, allows for the administration of high concentrations of oxygen, 60–90% O2.

Strictly, "non-rebreather" masks are "partial-rebreather" (PRB) masks; ideally, a non-rebreather mask would not permit air from the surrounding environment to be inhaled. However, since not all of the exhaled air is completely removed by the one-way valve and the seal created by the mask is imperfect, intake of some exhaled and outside air is unavoidable.

Usage
The non-rebreather mask is utilized for patients with physical trauma, chronic airway limitation/chronic obstructive pulmonary diseases, smoke inhalation, and carbon monoxide poisoning, or any other patient who requires high-flow oxygen, but does not require breathing assistance. Patients uncomfortable with having a mask on on their face, such as those with claustrophobia, or patient's with injuries to the mouth are more likely to benefit from a nasal cannula. Patient's who are unable to breathe on their own would require an active breathing device, such as a bag valve mask.