Correlation of bispectral index with end-tidal sevoflurane concentration and age in infants and children

The bispectral index (BIS) has been evaluated as a tool for measuring depth of anaesthesia, but the use of BIS in a paediatric population is still controversial. This study was designed to evaluate the correlation of BIS with end-tidal sevoflurane concentration and age in infants and children. Eighty-one patients undergoing elective urology surgery were allocated into three age groups; 6 months to 2 yr (n=28), 3–7 yr (n=33), and 8–12 yr (n=20). Sevoflurane was administered to achieve steady-state end-tidal sevoflurane concentrations (ETsevo) of 2.0, 3.0, and 4.0%; these were achieved consecutively either from the lowest or from the highest concentration. The BIS (version XP) was monitored continuously. In all three groups, BIS decreased significantly when ETsevo increased from 2.0 to 3.0% but there was a paradoxical increase in BIS values when ETsevo increased from 3.0 to 4.0%. The non-linear regression analysis showed a significant correlation between BIS and age at each ETsevo. The younger patients showed the higher BIS values. In children aged 6 months to 12 yr, the BIS increased paradoxically as ETsevo increased from 3.0 to 4.0%. BIS values showed a wide variation in the same ETsevo and the age itself was considered to be a factor affecting the BIS values.