The gas, nitrous oxide and newer agents, sevoflurane and desflurane are examples of very insoluble drugs. An agent with a low boiling point will evaporate easily and therefore be more available than one that has a high boiling point. Ether is highly volatile and thus there is almost no limit to the concentration that a vaporiser can give. Ether is really too volatile to be convenient and sometimes new, sealed bottles arrive with no agent inside, but at least it means we can give plenty of it to counteract its slow onset. Trichloroethylene, on the other hand, only reluctantly becomes a vapour and we have difficulty in getting it into the patient in sufficient quantities.
Halothane is in between and has a near-perfect profile of physical properties.
It indicates the maximum proportion of atmospheric pressure which can be occupied by the vapour of an agent. SVP is dependant only on the temperature and not on atmospheric pressure. Regardless of solubility and boiling point, each agent will have its own potency value. This is called the MAC - the Minimum Alveolar Concentration. Thus the potency of different agents can be compared by showing how much you need to produce the effect you want, expressed as a percentage vapour strength.