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 nitrous oxide (N2O) in combination with sevoflurane can attenuate cardiovascular responses to skin incision. To quantitatively evaluate their suppressive effects on cardiovascular responses, the authors compared the MAC-BAR (minimum alveolar concentration that blocks adrenergic or cardiovascular response to incision) values of sevoflurane when administered with Xe or N2O. Methods: Forty-three patients received sevoflurane with one of three anesthetics; 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 increased 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 calculated as the mean of four independent cross-over responses. Results: The MAC-BAR of sevoflurane, including the contribution of Xe or N2O, 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 MAC N2O (mean +/- SD). Conclusions: Although 1 MAC Xe has a more potent suppressive effect on cardiovascular responses to incision than 0.7 MAC Xe or N2O, Xe and N2O have a similar suppressive effect at 0.7 MAC.