Which feature prevents the filling of the vaporizer with the incorrect agent?

The agent-specific keyed filling ports are designed specifically to prevent the filling of a vaporizer with the wrong agent. Each inhalational anesthetic agent has its own unique port that can only accommodate one specific type of bottle, ensuring that practitioners cannot accidentally fill the vaporizer with an incorrect substance. This safety feature is crucial in medical settings, as mixing agents could lead to dangerous and unintended consequences in patient care.

In contrast, while the pin index safety system and the diameter index safety system are important for preventing equipment misconnection, they primarily focus on the attachment points for gas cylinders and anesthesia delivery devices rather than the actual filling of vaporizers. Counter-threading of the bottle attachment can add an extra layer of security but is generally a more mechanical method of ensuring proper attachment rather than specifically preventing the filling of incorrect agents.