Which volatile anaesthetic agent requires a temperature-controlled vapouriser because of its high vapor pressure?

• A. Isoflurane
• B. Desflurane
• C. Sevoflurane
• D. Nitrous oxide

Answer: (B)

Desflurane has a very high vapor pressure at room temperature because it is highly volatile (boiling point about -24°C). A vapouriser must deliver a precise concentration of anaesthetic by allowing liquid to vaporize into carrier gas. With such a high vapor pressure, even small temperature changes would cause big fluctuations in how much desflurane vaporizes, making the delivered dose unstable. To keep output stable, the desflurane vapouriser is heated and temperature-controlled, typically around body temperature, so the vapor pressure stays predictable. The other volatile agents have lower vapor pressures and can be delivered reliably by standard, ambient-temperature vapourisers. Nitrous oxide is a gas at room temperature and is not delivered through a liquid-filled, temperature-controlled vapouriser.