Minimum alveolar concentration: A reconsideration

Minimum alveolar concentration (MAC), served as the vital concept for standard measure of potency for inhaled volatile anesthetic agents, has been employed in anesthetic practice for more than 50 years. A re-consideration in the connotation and influence factors on MAC is introduced in this article. MAC actually indicates “median effective dose (ED50) for immobility”, but it is at least not comprehensive for MAC being as anesthetic potency, the total effects of inhaled volatile anesthetic agents. Without a strict “additive” nature, MAC is only the potency rather than efficacy, and the measured value of MAC usually is more than that of ED50 for the disappearance of righting reflex. Some factors, such as duration time of anesthesia, and the pattern, intensity and positions of stimulus, all can affect the measured value of MAC. In the future, in order to make MAC play more important and scientific role in the anesthetic practice, there should be an intensive study on the measured value of MAC of inhaled volatile anesthetic agents in different situations including the pattern, intensity and location of the stimulus.