The Bispectral Index in children: comparing isoflurane and halothane

The Bispectral Index (BIS) has been calibrated for several general anaesthetic agents including isoflurane. Halothane is still used in paediatric anaesthesia. Compared with other volatile anaesthetics, halothane has a different receptor affinity 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 isoflurane at a clinically relevant equipotent concentration (1 MAC) and at a reproducible measure of anaesthetic effect (awakening).

Forty children aged between 2 and 15 yr were enrolled in a masked randomized trial-20 in each group. Anaesthesia was induced with sevoflurane or propofol. Either halothane or isoflurane 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.

At 1 MAC the BIS for halothane was significantly greater than isoflurane (56.5 (8.1) vs 35.9 (8.5), P<0.0001). At awakening there was no significant difference (BIS halothane; 81.1 (11.9), BIS isoflurane; 82.5 (16.4)). The difference in means at awakening was 1.4 (95% CI -8.2 to 11.1).

At equipotent concentrations of halothane and isoflurane BIS valves were significantly greater with halothane. At awakening the BIS values were equivalent for each agent. This finding is consistent with the BIS being more affected by the agent used at higher concentrations of anaesthetic. The BIS must be interpreted with caution when using halothane.