Bispectral index monitoring in children undergoing mild hypothermic cardiopulmonary bypass

Background: In this prospective, cohort study of 15 children (median age 7.7 years, range 4.9-16.5 years) undergoing atrial septal defect repair, we evaluated changes in the Bispectral index (BIS) as a potential monitor of level of consciousness during cardiac anaesthesia. Methods: Identical cardiac surgery, cardiopulmonary bypass (CPB) and anaesthetic techniques were used, including mild hypothermia and an early extubation protocol. BIS, mean arterial pressure, heart rate and tympanic temperature were recorded at baseline postinduction (T-baseline)/ skin incision (T-incis), sternotomy (T-sternot), aortic cannulation (T-cann), nadir temperature (T-nadir), rewarmed (T-rewarmed), immediate post-CPB (T-postCPB), chest drain insertion (T-drains), sternal wires (T-wire), skin closure (T-closed) and spontaneous movement (T-move). As a measure of stress response, serum lactate, glucose, norepinephrine and epinephrine levels were measured at T-baseline, T-sternot, T-cann, T-nadir, T-rewarmed and T-drains. Explicit memory testing was undertaken prior to hospital discharge. Results: BIS increased significantly during the rewarming phase (T-rewarmed versus T-basline and T-nadir, P<0.001). Lactate, epinephrine and glucose levels were also significantly elevated at T-rewarmed. There were no correlations between BIS and the increase in epinephrine, lactate and glucose during rewarming, nor with changes in heart rate or mean arterial pressure during surgery. All patients had an uneventful recovery without evidence for explicit recall. Conclusions: The increase in BIS during the rewarming phase could reflect an increase in conscious level, and is consistent with the reported risk for awareness during this phase of cardiac surgery.