BACKGROUND: Cardiac anesthesia with cardiopulmonary bypass is associated with an increased risk of awareness. A new approach to intraoperative EEG procession, the bispectral index (BIS), may allow more reliable quantitative assessment of the level of consciousness during anesthesia. We evaluated the relationships between BIS and commonly used indices of depth of anesthesia in children.

METHODS: In the isoflurane group, anesthesia was maintained using isoflurane 0.5 1.0 vol% inhalation, whereas the fentanyl group received high dose fentanyl-midazolam infusion. BIS, mean arterial blood pressure, and heart rate were recorded at baseline, at postinduction (T^baseline), skin incision (T^incis), sternotomy (T^sterno), aortic cannulation (T^cannul), nadir temperature (T^nadir), immediate post-CPB (T^postCPB), sternal wire (T^wire), and at skin closure (T^close).

RESULTS: BIS showed a significant change over time (P < 0.001), with significant differences between groups (P = 0.04). BIS increased significantly during the immediate post-CPB phase (T^postCPB versus T^baseline, T^nadir, P < 0.01). No correlations were found between BIS and changes in heart rate or mean arterial pressure during surgery. BIS was higher in the fentanyl group than in the isoflurane group at T^incis, T^cannul, and T^wire (P < 0.05).

CONCLUSIONS: Even though BIS was relatively lower in the isoflurane group compared to the fentanyl group, we were still unable to demonstrate a relationship between the BIS and hemodynamic indices depth for any group. While the increase in BIS during the rewarming phase could reflect an increase in conscious level, larger prospective studies with postoperative memory test for awareness are necessary.