Frost develops on the outside of an N2O compressed-gas cylinder during general anesthesia. This phenomenon indicates that

Frost develops on the outside of an N2O compressed-gas cylinder during general anesthesia. This phenomenon indicates that

• A. The saturated vapor pressure of N2O within the cylinder is rapidly increasing
• B. The cylinder is almost empty
• C. There is a rapid transfer of heat to the cylinder
• D. The flow of N2O from the cylinder into the anesthesia machine is rapid

Answer: (D)

Frost on the outside of a nitrous oxide cylinder during anesthesia shows that a large amount of liquid N2O is rapidly vaporizing to replace the gas being drawn off. When gas leaves the cylinder, the liquid inside must boil to replenish the gas, which is an endothermic process. The heat drawn from the cylinder surface and surrounding environment causes the exterior to cool and frost forms. So the frost indicates rapid withdrawal of N2O from the cylinder into the anesthesia machine. The other options don’t fit as well: frost isn’t about the vapor pressure inside rising; it’s about heat being used to vaporize liquid, which cools the cylinder. Frost can occur even if the cylinder isn’t nearly empty. And the Frost results from cooling due to evaporation, not heat being transferred to the cylinder.

Frost on the outside of a nitrous oxide cylinder during anesthesia shows that a large amount of liquid N2O is rapidly vaporizing to replace the gas being drawn off. When gas leaves the cylinder, the liquid inside must boil to replenish the gas, which is an endothermic process. The heat drawn from the cylinder surface and surrounding environment causes the exterior to cool and frost forms. So the frost indicates rapid withdrawal of N2O from the cylinder into the anesthesia machine.

The other options don’t fit as well: frost isn’t about the vapor pressure inside rising; it’s about heat being used to vaporize liquid, which cools the cylinder. Frost can occur even if the cylinder isn’t nearly empty. And the Frost results from cooling due to evaporation, not heat being transferred to the cylinder.