Oxygen delivery is a foundational aspect of medical intervention, especially when a patient is experiencing difficulty breathing or low blood oxygen levels. Specialized tools are necessary to provide high concentrations of oxygen, which is crucial in acute medical situations. The Non-Rebreather Mask (NRB) is a highly effective device for rapidly increasing the fraction of inspired oxygen (FiO2) delivered to the patient. Correct usage depends entirely on setting the proper oxygen flow rate, which ensures the device delivers the highest possible oxygen concentration. The liter-per-minute setting is critical for patient safety.
What is a Non-Rebreather Mask and How Does it Work?
The Non-Rebreather Mask is a specialized oxygen delivery system designed to provide the highest possible concentration of oxygen to a spontaneously breathing patient. This system is composed of three main components: the face mask, a reservoir bag, and a series of one-way valves. Unlike low-flow devices like a nasal cannula, the NRB aims to minimize the entrainment of ambient air. The plastic face mask fits over the patient’s nose and mouth and connects to a reservoir bag that holds a supply of pure oxygen.
The unique function of the NRB relies on a one-way valve system placed between the mask and the reservoir bag. When the patient breathes in, this valve opens, allowing them to inhale oxygen directly from the reservoir bag. The valve immediately closes when the patient exhales, preventing carbon dioxide-rich air from flowing back into the pure oxygen supply. Additionally, one-way valves on the sides of the mask vent the exhaled air into the atmosphere, simultaneously blocking the inhalation of room air. This mechanism ensures the patient is breathing a high fraction of inspired oxygen (FiO2), typically ranging from 60% to 90%.
Determining the Minimum Flow Rate
The core requirement for the Non-Rebreather Mask to function properly is an adequate oxygen flow rate. The standard minimum recommended flow rate for an NRB is 10 to 15 Liters per Minute (LPM). This range is a necessary threshold to maintain the device’s high-concentration delivery integrity. The goal is to ensure the volume of oxygen flowing into the reservoir bag always exceeds the patient’s peak inspiratory flow demand.
The oxygen flow must be set high enough so the reservoir bag remains inflated during the patient’s entire breathing cycle. If the flow rate is insufficient, a patient taking a deep breath can rapidly empty the reservoir bag. This high flow rate is necessary because the patient’s inspiratory flow rate can be much higher than the flow meter setting, especially during respiratory distress. The 10 to 15 LPM setting serves as a safety margin, preventing the reservoir bag from completely collapsing when the patient inhales. The flow rate should be visually adjusted to keep the reservoir bag at least one-third to two-thirds full during the peak of inhalation.
Safety and Monitoring: The Importance of the Reservoir Bag
The visibility and inflation of the reservoir bag are the primary indicators of correct NRB function and patient safety. If the oxygen flow rate is set too low (e.g., below 10 LPM), the reservoir bag will deflate completely during the patient’s inhalation. This collapse is a safety failure because it compromises the one-way valve system that defines the NRB’s function.
When the reservoir bag collapses, the patient’s inhalation effort pulls air from the path of least resistance. In a properly functioning NRB, the patient draws exclusively from the pure oxygen in the reservoir bag. However, with a collapsed reservoir, the negative pressure created by the patient’s breath can cause the valve blocking exhaled air from entering the reservoir to malfunction. More significantly, it forces the patient to draw air from the side exhalation ports on the mask.
These exhalation ports are equipped with one-way valves designed to allow exhaled air out and prevent room air from entering. If the reservoir is empty, the patient may inhale the air they just exhaled, which is rich in carbon dioxide (CO2). This rebreathing of CO2 is precisely what the non-rebreather mask is designed to prevent, and it can rapidly worsen the patient’s condition by causing a buildup of CO2 in the blood. Therefore, the simple visual check that the reservoir bag remains partially inflated throughout the respiratory cycle is the most important monitoring step for safe NRB use.