The Bispectral Index in children: comparing iso¯urane and halothane

Background. The Bispectral Index (BIS) has been calibrated for several general anaesthetic agents including iso¯urane. Halothane is still used in paediatric anaesthesia. Compared with other volatile anaesthetics, halothane has a different receptor af®nity and differing effects on the EEG. There are limited data evaluating the BIS with halothane. We set out to compare the BIS using halothane and iso¯urane at a clinically relevant equipotent concentration (1 MAC) and at a reproducible measure of anaesthetic effect (awakening). Methods. Forty children aged between 2 and 15 yr were enrolled in a masked randomized trialÐ20 in each group. Anaesthesia was induced with sevo¯urane or propofol. Either halothane or iso¯urane were given to obtain an end-tidal concentration of 1 MAC for 15 min. The BIS was then recorded. The BIS was also recorded at awakening. Values (mean (SD)) were compared with a t test. Results. At 1 MAC the BIS for halothane was signi®cantly greater than iso¯urane (56.5 (8.1) vs 35.9 (8.5), P<0.0001). At awakening there was no signi®cant difference (BIS halothane; 81.1 (11.9), BIS iso¯urane; 82.5 (16.4)). The difference in means at awakening was 1.4 (95 % CI ±8.2 to 11.1). Conclusions. At equipotent concentrations of halothane and iso¯urane BIS valves were sig-ni®cantly greater with halothane. At awakening the BIS values were equivalent for each agent. This ®nding is consistent with the BIS being more affected by the agent used at higher concen-trations of anaesthetic. The BIS must be interpreted with caution when using halothane