How a Partial Rebreather Mask Works
A partial rebreather (PR) mask delivers moderate to high oxygen concentrations (40-70%) by allowing the patient to rebreathe approximately the first third of their exhaled breath, which comes from the anatomic dead space and contains minimal carbon dioxide, while the remainder is vented through side ports.
Basic Design and Components
- The PR mask consists of a face mask connected to a reservoir bag that fills with 100% oxygen from the oxygen source 1
- Unlike non-rebreather masks, the PR mask lacks one-way valves between the mask and reservoir bag, allowing bidirectional gas flow 2
- The mask has open exhalation ports on the sides that allow excess gas and the latter portion of exhaled breath (containing CO2) to escape 1
Mechanism of Operation
- During inhalation, the patient draws oxygen from both the reservoir bag and fresh oxygen flowing into the system 1
- The initial portion of each exhalation (approximately the first third) flows back into the reservoir bag, mixing with incoming fresh oxygen 3
- This exhaled gas comes from the anatomic dead space (trachea and upper airways) and contains primarily oxygen with minimal CO2 3
- The remainder of the exhaled breath, which contains higher CO2 concentrations from alveolar gas exchange, exits through the side ports 1
- During the next inhalation, the patient receives a mixture of fresh oxygen and this oxygen-rich exhaled gas from the reservoir 3
Flow Rate Requirements
- PR masks typically require oxygen flow rates of 6-10 L/min to function effectively 1
- The flow rate must be sufficient to keep the reservoir bag at least one-third to one-half full during inspiration 1
- If the bag completely collapses during inspiration, the flow rate is inadequate and should be increased 1
Delivered Oxygen Concentration
- PR masks deliver oxygen concentrations ranging from 40-70%, depending on the patient's respiratory rate, tidal volume, and oxygen flow rate 1
- This is lower than non-rebreather masks (which deliver 60-90% at 15 L/min) but higher than simple face masks (which deliver 40-60% at 5-10 L/min) 1
Clinical Considerations
- The PR mask is less commonly used in modern practice compared to non-rebreather masks or simple face masks because it offers an intermediate oxygen concentration that can usually be achieved more predictably with other devices 1
- For patients requiring high oxygen concentrations (>60%), a non-rebreather mask at 15 L/min is more appropriate 1
- For patients requiring moderate oxygen concentrations with precise control, Venturi masks provide more accurate FiO2 delivery 1