What Is Minimum Alveolar Concentration?

Concentration of inhaled anesthetics in alveolar air when 50% of people or animals lose evasive motor responses to noxious stimuli (such as incisions) under an atmospheric pressure. Expressed as a volume percentage. It is a quantitative indicator of the analgesic effect of various inhalation anesthetics or the strength of the anesthetic with numbers. The lower the MAC, the stronger the anesthetic effect. It is a quantitative indicator of the effectiveness of anesthetics. Its value can be changed due to the combined use of analgesics, sedatives and other factors. ^[1]

Minimum alveolar effective concentration

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The minimum effective alveolar concentration (MAC) of inhaled anesthetics was proposed by American anesthesiologist Eger et al. In 1965. MAC has now become the recognized main indicator for evaluating the potency of inhaled anesthetics, and it is also one of the means to explore the action site and mechanism of inhaled general anesthetics. At the same time, MAC is also used as an important reference index for judging the depth of clinical anesthesia and a measurement parameter for comparing the intensity of various operating stimuli.

Traditional MAC refers to the concentration of inhaled anesthetics in the alveolar gas when 50% of the animals do not respond to skin-cutting stimuli, that is, MAC-SI, also known as standard MAC. In recent years, with the continuous deepening of research on inhalation anesthesia, the concept of MAC has also been continuously extended, and a series of new concepts of MAC under different stimuli have appeared one after another. Such as commonly used MAC (MAC-EI) for tracheal intubation, MAC (EX) for tracheal extubation, MAC (LMI) for placement of the laryngeal mask, MAC (MAC-BAR) for suppressing sympathetic nerve response, and MAC-a for awake -wake), and MAC (MAC-BIS50), which blocks the vasomotor contractile reflex MAC (MAC-BVR) and EEG bispectral index values below 50 when cutting the skin, etc. ^[2]