Critical temperature is the temperature above which a compound cannot be liquefied by pressure alone.
When a compound is above its critical temperature
--> Gaseous form = gas
When a compound is below its critical temperature
--> Gaseous form = vapour
Thus, at room temperature
HAL, ENF, ISO, DES, SEVO, N2O are all vapours
Vapour pressure is pressure exerted by vapour
Saturated vapour pressure is the maximal pressure exerted by vapour at equilibrium
Total pressure exerted by a mixture of gas/vapour
= sum of partial pressure exerted by each of the component gases if present alone and occupying the same volume as the mixture
Tension is the pressure exerted by a gas/vapour within a solution
The state of anaesthesia is related to the tension of anaesthetics in the brain