Anesthetic doses of sevoflurane to block cardiovascular responses to incision when administered with xenon or nitrous oxide

Background The authors' previous study demonstrated that xenon (Xe) and nit rous oxide (N2O) in combination with sevoflurane can attenuate cardiovascul ar responses to skin incision. To quantitatively evaluate their suppressive effects on cardiovascular responses, the authors compared the MAC-BAR (min imum alveolar concentration that blocks adrenergic or cardiovascular respon se to incision) values of sevoflurane when administered with Xe or N2O. Methods: Forty-three patients received sevoflurane with one of three anesth etics; 1 MAC Xe, 0.7 MAC Xe and 0.7 MAC N2O. The MAC-BAR of sevoflurane was determined in each anesthetic using the "up and down" method. The response was considered positive if the heart rate or mean arterial pressure increa sed 15% or more. The end-tidal sevoflurane concentration given to the next patient was increased or decreased by 0.3 MAC if the response was positive or negative in the previous patient, respectively. The MAC-BAR was calculat ed as the mean of four independent cross-over responses. Results: The MAC-BAR of sevoflurane, including the contribution of Xe or N2 O, was 2.1 +/- 0.2 MAC and 2.7 +/- 0.2 MAC when administered with 1 MAC and 0.7 MAC Xe, respectively, and 2.6 +/- 0.4 MAC when administered with 0.7 M AC N2O (mean +/- SD). Conclusions: Although 1 MAC Xe has a more potent suppressive effect on card iovascular responses to incision than 0.7 MAC Xe or N2O, Xe and N2O have a similar suppressive effect at 0.7 MAC.