Minimum alveolar concentration

Minimum alveolar concentration (MAC) is the steady-state alveolar concentration of an inhaled anesthetic that prevents movement in 50% of patients exposed to a surgical incision. It measures anesthetic potency under specified conditions.

Alveolar partial pressure: The pressure exerted by a gas dissolved in or mixed with the air in the lung alveoli. At equilibrium, alveolar anesthetic partial pressure approximates the pressure at the brain that produces immobility.
General anesthesia: A drug-induced state of unconsciousness, amnesia, immobility, and reduced response to noxious stimuli during medical procedures. MAC is one inhaled-anesthetic potency measure within the broader practice of general anesthesia.
Isoflurane: A volatile inhalational anesthetic used to induce and maintain general anesthesia. Its potency is commonly reported as a MAC value, enabling comparison with other volatile agents.
MAC-BAR: The alveolar anesthetic concentration that blocks adrenergic responses to surgical stimulation in 50% of patients. It targets suppression of autonomic responses, requiring a higher concentration than movement-based MAC.
End-tidal anesthetic concentration: The concentration of anesthetic measured at the end of exhalation, used to estimate alveolar concentration. Clinicians use this measurable value as a practical estimate of the alveolar level defining MAC.
Inhalational anesthetic: A drug delivered through the lungs that produces reversible loss of sensation or consciousness. MAC applies to inhaled anesthetic agents, not intravenous anesthetics considered alone.
Sevoflurane: A volatile inhalational anesthetic widely used for induction and maintenance of general anesthesia. Its MAC helps clinicians interpret end-tidal concentrations during routine anesthetic delivery.
MAC-skin incision: The MAC estimate determined using movement response to a skin incision as the stimulus. It specifies the stimulus behind the standard endpoint, which can differ from other noxious stimuli.
Anesthetic immobility: The suppression of purposeful movement in response to a noxious stimulus during general anesthesia. MAC is defined by whether this response is prevented in half of exposed patients.
Surgical incision: A cut made through tissue during a surgical procedure. The standard stimulus for determining MAC is movement in response to a surgical incision.

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