Minimum blood concentration--a universal concept of anaesthetic potency.

Although brain concentration of anaesthetic agents is attractive as a method of expressing anaesthetic potency, both theoretical and practical considerations limit the usefulness of this index. Therefore, the MAC concept has been utilized to develop another expression of potency: the minimum blood concentration. This takes into account the blood/gas solubility coefficient, and the fact that at equilibrium the amount of anaesthetic agent present in brain is reflected in the blood concentration, and it is applicable to both parenteral and to inhalation anaesthetic agents.