Minimum alveolar concentration of sevoflurane that blocks the adrenergic response to surgical incision in women: MACBAR

We have investigated the cardiovascular and plasma noradrenaline response to surgical incision under sevoflurane anaesthesia and determined the end-tidal concentration of sevoflurane that blocks the adrenergic response or responses to surgical incision (MACBAR) and changes in mean arterial pressure (MAP) in response to surgical incision (MACBCR) in 50% of women. We randomly assigned 64 female patients, aged 20-49 years, to eight groups according to endtidal 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 noradrenaline concentration was considered a positive response. The probability of no response to stress was analysed using logistic regression to obtain the probability of no response vs. end-tidal sevoflurane concentration and the best-fit curve from the maximum likelihood estimators of the model parameters. MACBAR (mean±SE) was 8.0±0.2%, MACBCR was 7.9±0.2%. However, such high doses of sevoflurane cannot be used clinically because of their high toxicity. It may be preferable to combine sevoflurane with other anaesthetics to reduce haemodynamic responses to strong stimulation.