Volatile Anaesthetic Agents
Volatile anaesthetic agents are liquid at room temperature, but evaporate easily for administration by inhalation.
A volatile gas, such as Sevoflurane, diffuses from alveoli to the blood, following a concentration gradient, and continues diffusing until equilibrium is reached.

Very little of the agent is absorbed into the blood (low blood:gas partition coefficient), so diffusion is relatively fast. Only that fraction of the gas, which is not absorbed by the blood, contributes to anaesthesia.

Note: the following volatile agents produce amnesia and immobility, but not analgesia.

A higher cardiac output maintains the above concentration gradient, between the alveoli and blood, so it takes longer to reach a steady state (equilibrium) and, consequently, onset of anaesthesia also takes longer.

 Agent MAC %