THE MINIMUM ALVEOLAR CONCENTRATION (MAC) OF SEVOFLURANE WITH AND WITHOUT NITROUS-OXIDE IN ELDERLY VERSUS YOUNG-ADULTS

Study Objective: To determine the minimum alveolar concentration (MAC) of sevoflurane with and without 65% nitrous oxide (N2O) in non-Asian patients at least 70 years of age, and in patients aged 18 to 35 years . Design: Randomized open-study design. The Dixon up-down method deter mined the target sevoflurane concentration for each patient. Setting: Operating rooms of a large university hospital. Patients: 27 ASA statu s I and II patients aged 18 to 35 years and 26 patients at least 70 Te ars of age, who were free of any conditions or diseases that would int erfere with MAC determination. Interventions: Unpremedicated patients breathed savoflurane until the predetermined target end-tidal sevoflur ane concentration was reached for at least 15 minutes before skin inci sion. Up-down sevoflurane increments were 0.25% after an initial targe t concentration of 2%. This continued until there were at least three crossover pairs in each of the four groups. Measurements and Main Resu lts: Patients were observed for purposeful movement in response to a s kin incision. End-tidal sevoflurane, N2O and oxygen (O-2) concentratio ns were measured by a calibrated infrared analyzer. MAC was determined by logistic regression analysis. The MAC of sevoflurane in O-2/air fo r the mean age in each group was 2.6% in the younger group (age = 25 y r) and 1.45% in the elderly group (age = 76 yr). Nitrous oxide 65% dec reased MAC about 50% in each group at any age studied. Conclusions: Th e MAC of sevoflurane determined in this study is similar to that deter mined in previous studies, including the MAC determined in an elderly Asian population. Increasing age and N2O decrease sevoflurane MAC simi larly to that determined with other volatile anesthetics.