Minimum alveolar concentration of sevoflurane that blocks the adrenergic response to surgical incision in women: MAC(BAR)

We have investigated the cardiovascular and plasma noradrenaline response t o surgical incision under sevoflurane anaesthesia and determined the end-ti dal concentration of sevoflurane that blocks the adrenergic response or res ponses to surgical incision (MAC(BAR)) and changes in mean arterial pressur e (MAP) in response to surgical incision (MAC(BCR)) in 50% of women. We ran domly assigned 64 female patients, aged 20-49 years, to eight groups accord ing to end-tidal sevoflurane concentration: 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7 .5%, 8.0% and 8.5%. All patients received only sevoflurane anaesthesia. An increase of 10% or more from prestress (incision) values of MAP or plasma n oradrenaline concentration was considered a positive response. The probabil ity of no response to stress was analysed using logistic regression to obta in the probability of no response vs. end-tidal sevoflurane concentration a nd the best-fit curve from the maximum likelihood estimators of the model p arameters. MAC(BAR) (mean +/- SE) was 8.0 +/- 0.2%, MAC(BCR) was 7.9 +/- 0. 2%. However, such high doses of sevoflurane cannot be used clinically becau se of their high toxicity. It may be preferable to combine sevoflurane with other anaesthetics to reduce haemodynamic responses to strong stimulation.