Desflurane cannot be administered using a conventional variable bypass plenum vaporizer. The reason is best explained by which property of the agent?

• A Its blood gas partition coefficient of 0.42
• B Its vapour pressure of about 669 mmHg at 20 degrees C, close to atmospheric pressure ✓
• C Its low oil gas partition coefficient
• D Its tendency to react with soda lime

Explanation

Desflurane boils at approximately 23.5 degrees C, so its saturated vapour pressure at room temperature approaches one atmosphere. In a variable bypass vaporizer this would produce uncontrollably high output concentrations and make the splitting ratio impossible to calibrate. The Tec 6 vaporizer therefore heats the agent to 39 degrees C under pressure and metered pure vapour is mixed downstream. The low blood gas coefficient explains rapid kinetics, not the vaporizer design.

Reference: Miller's Anesthesia, 9th ed.

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