How many psi does a nitrous oxide cylinder have until fully liquid depleted?

• A. 500 psi
• B. 745 psi
• C. 850 psi
• D. 950 psi

Answer: (B)

The correct answer is 745 psi, which corresponds to the typical pressure of a nitrous oxide cylinder when it is filled with both liquid and gas. Nitrous oxide exists in a dual phase in a cylinder — the liquid phase at the bottom of the cylinder produces vapor pressure above it in the gas phase. As nitrous oxide is used, the pressure will drop until the liquid phase is almost fully depleted.

When about 20% of the liquid remains, the pressure in the cylinder is around 745 psi. This is a critical threshold for healthcare providers to note since it indicates that the liquid nitrous oxide is becoming low, and further use may lead to decreased efficacy or supply continuity. Once the cylinder is fully gaseous without the liquid phase, the pressure will drop significantly below this mark.

Understanding this specific pressure is essential for anesthesiologists and anesthesia providers to ensure safe and effective usage of nitrous oxide during procedures.