Which scenario best illustrates an open breathing system?

• A. A facemask delivering oxygen with room air
• B. An endotracheal tube in place
• C. A LMA with a closed circuit
• D. A sealed anesthesia circle

Answer: (A)

Open breathing systems are those where the patient breathes in and out of the environment rather than through a sealed, gas-recirculating circuit. A facemask delivering oxygen with room air fits this description because the gas mixture is not contained in a closed loop; oxygen is supplied, room air can be entrained, and the exhaled gases simply escape to the surrounding environment. There is no reservoir, valve, or sealed pathway that recirculates gases back to the machine.

In contrast, using an endotracheal tube attaches the patient to a breathing circuit, creating a contained loop where gases are delivered, potentially rebreathered, and managed within the system. A laryngeal mask airway with a closed circuit similarly establishes a controlled, semi-closed pathway. A sealed anesthesia circle represents a fully closed system with minimal exchange with the room.