Which mechanism on an anesthesia machine prevents connecting the wrong gas cylinder to the yoke by aligning pins and holes?

• A. Oxygen fail-safe
• B. Pin index safety system
• C. Pressure relief valve
• D. Flow sensor

Answer: (B)

Pin index safety system uses fixed pins on the yoke that must line up with matching holes on the cylinder valve. Each gas has a unique pin-hole pattern, so only the correct cylinder can be attached. This mechanical keying protects against connecting the wrong gas to the anesthesia machine, which is crucial for patient safety.

Other mechanisms do different jobs: an oxygen fail-safe manages the percentage of oxygen delivered if supply pressure changes, a pressure relief valve vents excess pressure, and a flow sensor monitors the actual flow. None of these prevent selecting or mating the wrong cylinder.