How can you make the line pressure gauge read zero?

To make the line pressure gauge read zero, depressing the oxygen flush valve allows high-flow oxygen to be released directly into the atmosphere, thereby decreasing the pressure in the system. When the oxygen flush valve is activated, it exits rapidly, and this sudden discharge of gas reduces the pressure in the circuit, resulting in the line pressure gauge showing a zero reading.

This action disrupts the equilibrium of the gas flow within the system, effectively venting the gas and allowing the pressure gauge to drop. In contrast, actions such as opening the vaporizer valve or closing the flowmeter valve would not effectively release enough gas to drop the pressure to zero. Additionally, releasing gas from the scavenging system is not designed to impact the line pressure gauge directly, as the scavenging system is more for managing excess anesthetic gases rather than affecting the pressure reading on the line pressure gauge.