Which factor does NOT increase MAC?

The correct choice is that acute ethanol (ETOH) does not increase the minimum alveolar concentration (MAC) of anesthetic agents. In fact, acute ethanol exposure is known to decrease MAC. This is because acute ethanol acts as a depressant on the central nervous system, often resulting in increased sensitivity to anesthetics, thereby requiring a lower concentration of the anesthetic to achieve the desired surgical anesthesia effect.

In contrast, chronic ethanol use can lead to tolerance, which tends to increase MAC values, as the body's adaptations to regular use require higher doses of anesthetics to achieve the same level of anesthesia. Serum sodium levels, particularly at extreme highs like 170 mEq/L, could potentially cause hypernatremia, which might also be associated with changes in consciousness or increased MAC. Hypothyroidism is known to decrease metabolism and can also lower MAC; however, it is important to note that the overall effect of metabolic state on MAC is complex.

Therefore, the unique effect of acute ethanol, compared to the other factors listed, is what designates it as the option that does not lead to an increase in MAC.