3. Old stuff
          3.1. Old pharm stuff (pre 2009)
              3.1.3. Pharmacology
                  3.1.3.2. Inhalational anaesthetic agents
 3.1.3.2.3. Physical properties of inhalational anaesthetics 

Physical properties of inhalational anaesthetics

Critical temperature

  • 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

  • Halothane, enflurane, isoflurane, desflurane, sevoflurane, and N2O are all vapours

Vapour pressure

  • Vapour pressure is pressure exerted by vapour
  • Saturated vapour pressure is the maximal pressure exerted by vapour at equilibrium

 

Dalton's law

  • 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

  • Tension is the pressure exerted by a gas/vapour within a solution
  • The state of anaesthesia is related to the tension (i.e. partial pressure) of inhalational anaesthetics in the brain
    * NOT concentration