Halogenated volatile agents

Question 1

Halogenated anaesthetic agents

What are, examples (6), characteristics.

Answer 1

Volatile agents
Liquids with a tendency to vaporise
Easily vaporise. Low boiling point, high saturated vapoir pressure

Commonly used:
* Sevoflurane
* Isoflurane
* Desflurane

No longer used in UK clinical practice:
* Ether
* Enflurane
* Halothane

Question 2

Vapours vs gases

Relation to critical temperature

Answer 2

• Gas: substances above their critical temperature exist only as gases, irrespective of how much pressure is applied
• Vapour is the gas phase of a substance at or below its critical temperature.

*Below their critical temperature, substances exist in both the liquid and gas forms (some molecules will have sufficient energey to leave the liquid and become a vapour by evaporation) and are termed vapours. *

Question 3

Boiling point

Definition

Answer 3

The temperature at which saturated vapour pressure = atmospheric pressure

At the boiling point, adding heat does not increase the temperature but it provides the latent heat of vaporisation which leads gas molecules to evaporate from the liquid phase.
-> the lower the boiling point, the more likely the agent will be in vapour phase at room temperature

Question 4

Saturated vapour pressure

Answer 4

= the pressure exerted by the vapour phase of a substance when in equilibrium with the liquid phase
(i.e. at a dynamic equilibrium where the number of molecules entering the liquid phase equals those leaving it and the vapour is therefore saturated).

SVP
* is an indication of the degree of volatility: i.e. the higher the SVP the more readily the agent will vaporise
*