What does a semi-closed breathing system utilize?

A semi-closed breathing system is characterized by its partial rebreathing ability, meaning that some of the exhaled gases are re-inhaled by the patient while fresh gas is added to the system. This setup is designed to conserve anesthetic agents and reduce waste, offering both efficiency and safety during anesthesia.

In a semi-closed system, a reservoir is used to store exhaled gases, which allows for a mix of fresh gas and the rebreathing of previously exhaled gases. This balance provides a consistent supply of anesthetic agents while also taking advantage of the rebreathing capability, which helps to maintain adequate anesthetic depth and reduce anesthesia costs.

Other breathing systems might either not use a reservoir at all, resulting in no rebreathing, or use very high fresh gas flows that lead to complete rebreathing. The key feature of the semi-closed system is its strategic use of a reservoir that facilitates partial rebreathing. This makes it distinct from both fully closed systems, which operate at low flows with complete rebreathing, and open systems, which do not retain any exhaled gases. Thus, the correct choice encapsulates the essential characteristics of a semi-closed breathing system.