The most common way to measure inhaled anesthetic potency is by recording the minimum alveolar concentration (MAC) needed to prevent movement to a painful stimulus. The MAC concentrations are recorded at 1 atmosphere and reported as the mean concentration needed to abolish movement in 50% of subjects. The MACs for the inhaled anesthetics are listed in Table 22.1. Potency of the inhaled anesthetics is extremely important as the anesthetic gas is displacing oxygen in the inspired gas. Inhaled agents with low potencies (high MACs) such as nitrous oxide require administration at increased pressure or are used only in combination with more potent inhaled agents.
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