Women appear to have the same minimum alveolar concentration as men: a retrospective study

A recent report finds that elderly Japanese women given xenon have a significantly smaller (26% less) MAC (minimum alveolar concentration required to eliminate movement in response to surgical incision in 50% of patients) than Japanese men of the same age. The authors assessed whether this finding applied to other/all anesthetics.

The authors reviewed data obtained previously for 258 patients (127 women and 131 men) anesthetized with desflurane, diethyl ether, halothane, methoxyflurane, sevoflurane, or xenon. Data were normalized to the MAC for the anesthetic as determined by logistic regression (i.e., MAC would equal a value of 1.000).

The MAC for the normalized combined (all) data for women (1.013 +/- 0.017; mean +/- SEM) did not differ significantly from the normalized combined data for men (1.005 +/- 0.009), and neither differed significantly from 1.000. However, a significantly smaller MAC value was found for women in two studies of sevoflurane (subsets of the above studies) given to Japanese patients: 12% in one study and 16% in the other.

Overall, no difference in MAC was found for women versus men. Whether women (particularly older Japanese women) have a smaller MAC than men remains to be confirmed by prospective studies.