A nonrebreather (NRB) mask is used primarily in emergency situations to deliver the highest possible concentration of oxygen to a patient who is still breathing. It utilizes a one-way valve system and an attached reservoir bag filled with oxygen, ensuring that the air the patient exhales does not mix with the fresh oxygen supply. While highly effective for rapidly increasing blood oxygen levels, the nonrebreather mask has limitations that restrict its widespread and long-term use.
Dependency on High Oxygen Flow
The primary limitation of the nonrebreather mask is its reliance on a high, continuous flow of oxygen. The reservoir bag attached to the mask must remain inflated, or at least partially inflated, even at the end of the patient’s deepest breath. This requirement typically necessitates an oxygen flow rate of 10 to 15 liters per minute (L/min) to prevent the bag from fully collapsing.
If the oxygen supply runs low or the flow rate drops below the minimum, the patient will quickly deplete the reserve of oxygen inside the bag. Because the mask’s one-way valves prevent the patient from drawing in outside air, a deflated reservoir bag presents a risk of suffocation. This high consumption rate rapidly depletes portable oxygen tanks, which is a major logistical concern in pre-hospital and transport settings.
Challenges in Maintaining a Secure Seal
The high oxygen concentration can be diluted if a secure seal is not maintained. The mask is designed to fit snugly over the nose and mouth, but any gap allows ambient air to be drawn in, which contains only about 21% oxygen. This compromises the therapeutic goal of delivering an oxygen fraction between 60% and 90%.
Various physical factors make achieving and sustaining this tight seal difficult. Facial hair, for example, can create channels for air leakage between the skin and the mask’s edges, significantly reducing the intended oxygen concentration. Additionally, structural irregularities like facial trauma, missing teeth, or the patient’s agitation can prevent the mask from conforming properly to the face.
Patient Tolerance and Communication Difficulties
The physical design of the nonrebreather mask introduces limitations related to patient comfort and interaction. Because the mask covers the entire nose and mouth and is secured tightly by elastic straps, many patients experience feelings of claustrophobia. This discomfort can lead to anxiety and agitation, sometimes causing the patient to attempt to remove the device.
The mask creates significant barriers to routine care and communication. The patient cannot eat or drink while the mask is in place, which is a concern even for short periods. The bulky plastic covering muffles speech, making it challenging for the patient to communicate their needs or for providers to hear them clearly.
Constraints on Extended Use
Nonrebreather masks are intended for short-term, acute use, and are not appropriate for prolonged oxygen therapy due to physiological constraints. Unlike other oxygen delivery systems, the NRB mask typically delivers dry, unhumidified oxygen. Over hours of use, this dry gas can irritate and dry out the mucous membranes in the patient’s nose, mouth, and throat, causing discomfort.
Extended use also introduces the risk of skin breakdown and pressure injuries from the mask itself. Localized pressure exerted by the mask and its elastic straps, particularly across the bridge of the nose and the cheeks, can compromise skin integrity. This pressure, combined with the moisture and heat trapped under the plastic, creates a microclimate that increases the risk of developing pressure ulcers.