Currently, monitoring during general anesthesia maintained with a volatile anesthetic includes real-time measurement of its end-tidal partial pressure (FET), displayed on the workstation as concentration and often also as fraction of minimum alveolar concentration (fMAC) or age-adjusted fMAC. The current review explains how proper understanding of the minimum alveolar concentration (MAC) and fMAC concept will help the clinician to titrate volatile anesthetics. Table 1 lists the most frequently used abbreviations and acronyms. Figures and dosing examples are mainly used to explain concepts; we clearly mention whether a figure or part of a figure is based on patient data.

MAC has been defined by Ted Eger and Lawrence Saidman1,2  as the steady-state minimal alveolar concentration that results in immobility in 50% of animals and humans after application of a noxious stimulus. In animals, to determine MAC, they are anesthetized with the study drug in the absence...

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