MAC-awake of sevoflurane in children


Dr A.J. Davidson, Department of Anaesthesia, Royal Children’s Hospital, Flemington Road, Parkville 3052, Vic., Australia (email:


Introduction:  Age influences the potency of anesthetic agents, but there is little information on how age influences MAC-awake. MAC-awake may be an important aspect of anesthesia potency for the prevention of awareness during anesthesia. The aim of this study was to measure MAC-awake in a range of ages in children.

Methods:  After institutional ethics approval and informed parental consent 60 children were enrolled; 20 in each of three age groups (2 to <5, 5 to <8 and 8–12 years). Children were excluded if they had opioids, sedative premedication or a procedure likely to cause any residual discomfort. All children had sevoflurane anesthesia. At the end of the procedure the sevoflurane was decreased to the target concentration. Once the target endtidal concentration was achieved it was maintained for 10 min before a standard stimulus was applied and an observer determined if the child was awake. The Dixon up–down method was used to determine progression of subsequent concentrations and MAC-awake (ED50) for the three age groups were obtained using the probit model.

Results:  This study found evidence for a difference in ED50 between age groups (P = 0.008). The MAC-awake was highest in the youngest group (0.66%) and similar in the older groups (0.45% and 0.43%).

Conclusion:  Although MAC-awake changes with age, in the ages where awareness has been reported, MAC-awake was found to be relatively low, and therefore it seems unlikely that age-specific changes to MAC-awake are a cause for awareness in children aged 5–12 years.