Minimum alveolar concentration

Minimum alveolar concentration (MAC) is the concentration, often expressed as a percentage by volume, of a vapour in the alveoli of the lungs that is needed to prevent movement in 50% of patients in response to pain. MAC is used to compare the potency (dose required to induce a specific effect) of anaesthetic vapours. The concept of MAC was first introduced in 1965.

"Minimum alveolar concentration" is a misnomer, as MAC is representative of a median value. The original paper proposed MAC as the minimal alveolar concentration, which was shortly thereafter revised to minimum alveolar concentration. A lower MAC value represents a more potent volatile anesthetic.

Other uses of MAC include MAC-BAR (1.7–2.0 MAC), which is the concentration required to block autonomic reflexes to nociceptive stimuli, and MAC-awake (0.3–0.5 MAC), the concentration required to block voluntary reflexes and control perceptive awareness.

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