A nonrebreather mask (NRB) is a medical device used to deliver the highest possible concentration of oxygen to a patient who is still able to breathe on their own. It is designed for use when a person requires immediate supplemental oxygen due to low blood oxygen saturation. The NRB is a high-flow system that ensures the patient primarily inhales oxygen, minimizing the dilution that occurs with room air. It is used in acute care settings to treat conditions that cause severe oxygen deprivation.
Anatomy and Key Components
The nonrebreather mask consists of a face mask that covers the nose and mouth, secured with an elastic strap. Attached to the bottom of the mask is the reservoir bag. This bag serves as a holding chamber for the oxygen supply before it is inhaled by the patient.
The mask incorporates one-way valves. One valve is positioned between the face mask and the reservoir bag. Two additional valves are located on the side ports of the mask, which are the openings through which exhaled air vents.
The Mechanism of Oxygen Delivery
The NRB achieves its high concentration of delivered oxygen using its one-way valve system. The reservoir bag is continuously filled with oxygen from an external source, typically at a flow rate of 10 to 15 liters per minute.
When the patient takes a breath, the one-way valve between the mask and the reservoir bag opens, allowing the patient to draw oxygen from the bag into the mask. The one-way valves on the side ports of the mask close, preventing the patient from drawing in room air that would dilute the oxygen concentration. This ensures the inspired gas is supplemental oxygen.
Upon exhalation, the valve to the reservoir bag closes, preventing exhaled, carbon dioxide-rich air from entering the oxygen supply in the bag. The patient’s breath is vented through the side ports of the mask. This mechanism prevents the rebreathing of carbon dioxide and allows the patient to receive an inspired oxygen concentration (FiO2) ranging from 60% to over 90%.
Clinical Usage and Indications
The nonrebreather mask is used for medical situations that demand an immediate increase in blood oxygen levels. It is used when a patient is experiencing hypoxemia, or low oxygen in the blood, but is still breathing without assistance. High-flow oxygen delivery is necessary in cases of physical trauma, such as chest injuries.
The device is used for toxic exposures, including smoke inhalation and carbon monoxide poisoning. In carbon monoxide poisoning, the high concentration of oxygen helps to displace the carbon monoxide molecules that are bound to hemoglobin in the bloodstream, allowing the blood to recover its oxygen-carrying capacity more quickly. For patients experiencing cluster headaches, high-flow oxygen via an NRB has been shown to be an effective treatment option. The NRB is used when lower-flow devices, such as a nasal cannula, would be insufficient to meet the patient’s oxygen needs.