How does a partial rebreather mask work?

How does a partial rebreather mask work?

• A. Delivers fixed 100% FiO₂ at 15 L/min
• B. Uses nasal prongs to deliver low FiO₂
• C. Uses a reservoir bag to capture some exhaled gas for rebreathing; delivers higher FiO₂ (6-15 L/min)
• D. Allows only expired air to escape

Answer: (C)

Partial rebreather masks raise the oxygen concentration by using a reservoir bag to capture part of the exhaled breath and allow it to be rebreathed on the next inhale. When you breathe in, you draw air from both the oxygen flow and the gas in the reservoir. Some of the exhaled air fills the bag and, on the next breath, combines with fresh oxygen, increasing the fraction of inspired oxygen compared with a simple mask. The mask still vents some gas to prevent CO2 buildup, so you don’t rebreathe all of the exhaled air. This setup typically requires a relatively high flow, about 6–15 L/min, to keep the bag partially inflated and to maintain the higher FiO2, often around 60–75% depending on fit and patient breathing. So the best description is that it uses a reservoir bag to capture some exhaled gas for rebreathing and delivers higher FiO2 at those flow rates.

Partial rebreather masks raise the oxygen concentration by using a reservoir bag to capture part of the exhaled breath and allow it to be rebreathed on the next inhale. When you breathe in, you draw air from both the oxygen flow and the gas in the reservoir. Some of the exhaled air fills the bag and, on the next breath, combines with fresh oxygen, increasing the fraction of inspired oxygen compared with a simple mask. The mask still vents some gas to prevent CO2 buildup, so you don’t rebreathe all of the exhaled air.

This setup typically requires a relatively high flow, about 6–15 L/min, to keep the bag partially inflated and to maintain the higher FiO2, often around 60–75% depending on fit and patient breathing. So the best description is that it uses a reservoir bag to capture some exhaled gas for rebreathing and delivers higher FiO2 at those flow rates.