Which volatile anaesthetic agent must be delivered via a temperature-controlled vapouriser due to its properties?

• A. Isoflurane
• B. Halothane
• C. Desflurane
• D. Sevoflurane

Answer: (C)

Desflurane has a very low boiling point and very high vapor pressure, so it readily vaporizes at room temperature. A standard variable-bypass vapouriser relies on a controlled mix of liquid agent and carrier gas, and its output is sensitive to ambient temperature. If desflurane were used in a normal vapouriser, small changes in temperature or gas flow could cause large, unpredictable swings in the amount delivered, risking overdose or under-dosing. To provide a precise, safe concentration, desflurane must be delivered through a temperature-controlled (heated) vapouriser that maintains a constant vapor pressure regardless of ambient conditions. Other agents with higher boiling points can be delivered safely with standard vapourisers, so they don’t require this special heating.