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Reference.org
Minimum alveolar concentration
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<p>Minimum alveolar concentration or MAC is the concentration, often expressed as a percentage by volume, of a vapour in the alveoli of the <a href="/facts/Lung/gTWXI6Fj">lungs</a> that is needed to prevent movement (motor response) in 50% of subjects in response to surgical (pain) stimulus. MAC is used to compare the strengths, or <a href="/facts/Potency_(pharmacology)/D38FDyPh">potency</a>, of anaesthetic <a href="/facts/Volatile_anaesthetic/INHvFCPk">vapours</a>. The concept of MAC was first introduced in 1965. </p><p>MAC actually is a <i>median</i> value, not a minimum as term implies. The original paper proposed MAC as the <i>minimal</i> alveolar concentration, which was shortly thereafter revised to <i>minimum</i> alveolar concentration. A lower MAC value represents a more potent volatile anesthetic. </p><p>Other uses of MAC include MAC-BAR (1.7–2.0 MAC), which is the concentration required to block <a href="/facts/Autonomic_nervous_system/hdmEY1Ay">autonomic</a> reflexes to <a href="/facts/Nociception/v0DsC73C">nociceptive stimuli</a>, and MAC-awake (0.3–0.5 MAC), the concentration required to block voluntary reflexes and control perceptive awareness. </p>