MAC Values

MAC, the minimum alveolar concentration of an inhaled anesthetic, provides anesthesiologists with a convenient mental model of anesthetic potency as a basis for clinical decisions. Philips IntelliVue patient monitors calculate MAC and MAC-awake* values for display on the monitor using the gas concentration measurements provided by Philips gas modules.

The partial pressure of the brain and alveoli are in equilibrium; therefore, alveolar concentrations can be used to gauge the anesthetic effect of an inhaled agent.

A MAC value of 1 is defined as the alveolar concentration at which 50% of a patient population does not respond with movement to a noxious stimulus, such as skin incision. MAC is a valuable measure because it applies to any inhaled agent, including N₂O.

Similarly, a MAC-awake* value of 1 signifies the anesthetic agent concentration at which 50% of patients respond again to verbal comment.

MAC is a useful indicator of anesthetic potency in one normalized value since the required concentrations of different agents to achieve a MAC value of 1 varies widely.

In addition to the standard MAC calculation, our algorithm can also calculate a corrected and enhanced MAC* value.

Corrected MAC takes into account:

• ambient barometric pressure
  

Enhanced MAC* that also takes into account:

• patient age
• body temperature