Age-related iso-MAC charts for isoflurane, sevoflurane and desflurane in man

Background. The motivation for this study was the current difficulty in estimating the total age-related MAC for a patient in a clinical setting. Methods. Age-related iso-MAC charts for isoflurane, sevoflurane and desflurane were developed for the clinically useful MAC range (0.6-1.6), age range 5-95 yr, and put in a convenient form for use by practising anaesthetists. The charts are based on Mapleson's meta-analysis (1996) of the available MAC data and can be used to allow for the contribution of nitrous oxide to the total MAC. Results. The charts indicate the influence of age on anaesthetic requirements, showing, for example, that a total MAC of 1.2 using isoflurane and nitrous oxide 67% in oxygen requires an end-expired isoflurane concentration of only 0.25% in a patient of 95 yr vs 1% in a 5-yr-old patient. Colleagues found the charts to be helpful and simple to use clinically. Conclusions. The iso-MAC charts show clearly how patient age can be used to guide the choice of end-expired agent concentration. They also allow a consistent total MAC to be maintained when changing the inspired nitrous oxide concentration, thereby reducing the chance of inadvertent awareness, particularly at the extremes of age.