Which device is used to evacuate excess nitrous oxide from a patient’s breathing space?

The correct option is the nitrous oxide nose mask, which is designed specifically to deliver nitrous oxide to the patient while minimizing the exposure of dental professionals to the gas. This mask has an effective seal around the patient's nose, which allows for the controlled inhalation of nitrous oxide and oxygen, creating a safer environment by limiting the escape of nitrous oxide into the surrounding area.

While other devices such as a high-volume evacuator or a low-volume saliva ejector play vital roles in the dental practice, their primary functions do not specifically target the evacuation of nitrous oxide from a patient's breathing space. The high-volume evacuator is generally used for removing saliva, blood, and other debris during dental procedures, but it is not particularly designed for controlling the levels of nitrous oxide in the air. The low-volume saliva ejector serves a similar role, focusing primarily on removing smaller amounts of saliva rather than gases like nitrous oxide. The nitrous oxide flowmeter is essential for regulating the delivery of nitrous oxide during treatment but does not address the evacuation of excess gas from the environment once administered.