BACKGROUND AND GOAL OF STUDY: Bispectral Index (BIS) has been used in adults to measure depth of anesthesia using various protocols. Though less investigated in children, there is growing evidence that bispectral index seems adequately calibrated for monitoring the depth of isoflurane and sevoflurane anesthesia in pediatric patients. A range of BIS scores (40-60) has been seen to be an indicator for an acceptable level of hypnosis and anesthesia. Davidson and Czarnecki have reported that, at an end-tidal concentration of 1 MAC, the BIS for halothane was significantly greater than isoflurane (56.5 +/- 8.1 vs. 35.9 +/- 8.5). The explanation given is the fact that the volume concentration of the MAC value is inversely related to the BIS value. Accordingly, it is expected that the BIS value at 1 MAC of desflurane must be less than halothane and isoflurane.
Materials and methods: This is a clinical cross-over, prospective, randomized double blinded study. 90 pediatric patients scheduled for below umbilical surgery, under general and caudal analgesia, were allocated into 4 study groups. The BIS values at a relatively equipotent doses of the previously mentioned agents were compared with each other in the same group and between other groups.
Results: At a relatively equipotent doses, the mean BIS value for halothane {60.4 +/- 5.6} was significantly higher than isoflurane {45.5 +/- 9.2} and desflurane {38.5 +/- 9.2} P<0.001). Equivalent end-tidal doses of different inhalational anesthetics do not necessarily have the same effects on cortical and sub-cortical functions and consequently on EEG.
Conclusion: The use of a relatively equipotent end-tidal concentration of different inhalational agents may result in different BIS values.