Which medical gas is primarily used as a pain-relieving agent?

Nitrous oxide is primarily used as a pain-relieving agent due to its analgesic and anesthetic properties. It is commonly referred to as "laughing gas" and is often used in dental procedures, labor and delivery, and in some surgical environments to provide sedation and relieve pain. The mechanism of action involves the modulation of pain pathways in the central nervous system, making it effective for short-term procedures where rapid onset of pain relief is desired.

In contrast, carbon dioxide is utilized mainly for insufflation in laparoscopic surgery and for other physiological functions rather than direct pain relief. Oxygen is essential for cellular metabolism and is administered to enhance oxygenation during respiratory distress but does not provide analgesic effects on its own. Helium is primarily utilized in combination with oxygen to facilitate breathing in certain medical conditions like obstructive airway diseases, but it does not act as a pain-relieving agent. Therefore, nitrous oxide stands out as the primary medical gas employed for pain relief.