Which of the following is NOT a gas used for anesthesia?

Carbon dioxide is not used as an anesthetic gas. In the context of anesthesia, gases like nitrous oxide, oxygen, and medical air play significant roles in providing anesthetic effects or maintaining patient physiology during surgery.

Nitrous oxide is a commonly used anesthetic gas that provides analgesic and sedative effects, often used in combination with other agents. Oxygen is essential for maintaining tissue oxygenation, supporting respiration during anesthesia. Medical air, which is a mixture of oxygen and nitrogen at atmospheric pressure, is used to provide a safe environment for inhalation during anesthesia.

Carbon dioxide, on the other hand, is a waste product of metabolism and is not used for anesthesia. It is typically monitored during surgical procedures to ensure proper respiration and metabolic function but does not provide the analgesic or anesthetic properties necessary for surgical interventions. Therefore, it does not classify as an anesthetic gas.