The gauge at the top of the nitrous oxide tank is used to determine the amount left in the tank.

• A. True
• B. False
• C. It measures the pressure of the gas in the tank
• D. It indicates the vaporizer setting

Answer: (B)

The main idea is that the gauge on a nitrous oxide cylinder is a pressure gauge, not a direct measure of how much gas remains. Nitrous oxide is stored as a liquid with a small amount of gas above it, so the pressure inside the tank stays relatively constant as gas is withdrawn. Because of this liquid–gas behavior, the current pressure doesn’t reliably indicate remaining volume. The gauge won’t tell you how much gas is left, and the vaporizer setting is a separate control on the anesthesia system, not the cylinder’s pressure gauge. To estimate remaining gas, you’d use a method tied to weight or a dedicated contents gauge, not the pressure reading.