The ratio of nitrous oxide to oxygen in a gas mixture must be what?

• A. 1:1
• B. 2:1
• C. 3:1
• D. 1:2

Answer: (B)

The main idea is balancing analgesia from nitrous oxide with safe oxygenation. Nitrous oxide provides the anesthetic effect, but it cannot meet the body’s oxygen needs on its own, so a sufficient amount of oxygen must be included in the gas mixture. The standard mix uses two parts nitrous oxide to one part oxygen, giving about two-thirds N2O and one-third O2. This gives enough nitrous oxide to achieve anesthesia while ensuring an adequate inspired oxygen concentration (roughly FiO2 around 0.33) to keep tissues well-oxygenated. Ratios with more oxygen (and less nitrous oxide) would fail to provide adequate analgesia, while ratios with more nitrous oxide and less oxygen risk hypoxia.