Minimum alveolar concentration (MAC) of xenon with sevoflurane in humans

Background: Although more than 30 yr ago the minimum alveolar concentration (MAC) of xenon was determined to be 71%, that previous study had technolog ical limitations, and no other studies have confirmed the MAC value of xeno n since. The current study was designed to confirm the MAC value of xenon i n adult surgical patients using more modern techniques. Methods: Sixty patients were anesthetized with sevoflurane with or without xenon. They were randomly allocated to one of four groups; patients in grou p 1 received no xenon, whereas those in groups 2, 3, and 4 received end-tid al concentrations of 20, 40, and 60%, respectively (n = 15 each group). Tar get end-tidal sevoflurane concentrations were chosen using the "up-and-down " method in each group. After steady state sevoflurane and xenon concentrat ions were maintained for at least 15 min, each patient was monitored for a somatic response at surgical incision. Somatic response was defined as any purposeful bodily movement. The MAC of sevoflurane and its reduction by xen on was evaluated using the multiple independent variable logistic regressio n model. Results: The interaction coefficient of the multiple variable logistic regr ession was not significantly different from zero (P = 0.143). The MAC of xe non calculated as xenon concentration that would reduce MBC of sevoflurane to 0% was 63.1%. Conclusions: The authors could not determine whether interaction in blockin g somatic responses in 50% of patients is additive. The MAC of xenon is in the range of the values that were predicted in a previous study.