In rebreathing anesthesia systems, what type of gas reaches the animal's lungs?

• A. A mixture of fresh and scavenged gas
• B. Only the anesthetic gas
• C. Only fresh carrier gas
• D. A mixture of fresh and exhaled gases

Answer: (D)

In rebreathing anesthesia circuits, the gas the animal inhales is recirculated after removing CO2. The fresh gas flow adds oxygen and anesthetic to the loop, while the exhaled gas that has passed through the carbon dioxide absorber is mixed back in. The result is a breath that is a blend of fresh carrier gas (with anesthetic) and exhaled gas that has been scrubbed of CO2. The exact mix depends on the fresh gas flow relative to the animal’s breathing, so the lungs receive a combination of both fresh and rebreathed gases.