Which of these gases is NOT considered a medical gas?

The choice of nitrogen as the gas that is not considered a medical gas is grounded in its primary uses and characteristics. Medical gases are typically defined as gases that are used for therapeutic or diagnostic purposes in a medical setting.

Oxygen is vital for patient care, commonly used in respiratory therapy to treat hypoxia. Carbon dioxide, while not used in therapy in the same way, plays a critical role in medical procedures, such as in insufflation during laparoscopic surgery. Helium is utilized in specific cases, often in combination with oxygen, for respiratory issues, since it can help reduce airway resistance.

In contrast, nitrogen is primarily an inert gas used in various industrial applications and does not play a therapeutic role in patient management. While it is present in the air we breathe and can be used to maintain a sterile environment or to drive certain medical devices, it does not provide any direct medical benefit when administered to patients. Therefore, nitrogen is distinct from the other gases listed, making it the correct answer for this question.