Standard MAC values assume the absence of all other potentially sedative or hypnotic drugs. The standard deviation of MAC is ~10%, thus 95% of patients will not respond to 1.2 MAC, and 99% will not respond to 1.3 MAC.
The Minimum Alveolar Concentration (MAC) of an inhaled anesthetic is the alveolar (or end-expiratory) concentration at which 50% of patients will not show a motor response to a standardized surgical incision. There is consensus that inhaled anesthetics produce anesthesia by enhancing inhibitory channels and attenuating excitatory channels, but whether or not this occurs through direct binding or membrane alterations is not known. Inhaled anesthetics produce immobility via actions on the spinal cord. Other than nitrous oxide (which increases skeletal muscle tone), inhaled anesthetics either do not affect, or in some cases lower skeletal muscle tone Mechanism of Action They do, however, produce immobility and amnesia. Surrogate measures of pain suggest that, with the exception of nitrous oxide, inhaled anesthetics do not provide any significant analgesia. Molecular structure of common inhaled general anesthetics Actions