Initial fresh gas flow range for a circle circuit?

• A. 5-6 L/min
• B. 2-4 L/min
• C. 0.5-1 L/min
• D. 1-2 L/min

Answer: (B)

Getting the circle system ready relies on a fresh gas flow high enough to quickly replace the gas inside the circuit and establish the desired inspired concentrations. If you start too low, it takes longer to wash out room air and bring the patient’s alveolar and thus end-tidal concentrations up to the target level. If you push flow too high, you waste gas and vent more anesthetic than needed. In typical small-animal practice, a starting flow of about 2–4 L/min provides a good balance: it fills the circuit promptly and achieves rapid wash-in of oxygen and anesthetic vapor. Once the depth of anesthesia is established and the circuit is primed, you decrease to maintenance flows (often around 0.5–1 L/min for very small patients or 1–2 L/min depending on size) to conserve gas while maintaining stable anesthesia.