Background: Entropy and Bispectral Index (BIS) have been promoted as EEG-based anaesthesia depth monitors. The EEG changes with brain maturation, but there are limited published data describing the characteristics of entropy in children, and some data suggest that BIS is less reliable in young children. The aim of this study was to compare the performance of entropy as a measure of anaesthetic effect in different age groups. The performance of entropy was compared with BIS.
Methods: Fifty-four children receiving a standard sevoflurane anaesthetic for cardiac catheter studies were enrolled. The entropy and BIS were recorded pre-awakening and at 1.5%, 2% and 2.5% steady-state end-tidal sevoflurane concentrations. For analysis children were divided into four age groups: 0-1 yr, 1-2 yr, 2-4 yr and 4-12 yr.
Results: The pre-awakening values were obtained in 46 children. The median pre-awakening values for entropy and BIS varied significantly across ages with the values being lowest in the 0-1 yr age group (response entropy: 45 vs 84, 87 and 89, P=0.003; state entropy: 36 vs 78, 74 and 77, P=0.009; BIS: 56 vs 78, 76.5 and 72, P=0.02). Values were recorded at all three sevoflurane concentrations in 48 children. Compared with older groups, the 0-1 yr age group had the least significant difference in BIS and entropy when compared among different sevoflurane concentrations. The calculated sevoflurane concentrations to achieve mid-scale values of entropy and BIS were highest in the 1-2 yr age group, lower in the 0-1 yr age group and progressively lower in the 2-4 and 4-12 yr age groups.
Conclusions: For both entropy and BIS the measure of anaesthetic effect was significantly different for children aged <1 yr compared with older children. There was no difference in performance of entropy and BIS. Both should be used cautiously in small children.