Bispectral index monitoring during infant cardiac surgery: relationship ofBIS to the stress response and plasma fentanyl levels

Background: We evaluated the relationship of the bispectral index (BIS) to commonly used indices of depth of anaesthesia in 19 infants enrolled in a p rospective study of the stress response to hypothermic cardiopulmonary bypa ss. Methods: Group 1 (n=8) received high-dose fentanyl by bolus technique; grou p 2 (n=6) received high-dose fentanyl by continuous infusion; and group 3 ( n=5) received a fentanyl-midazolam infusion. Blood pressure (BP), heart rat e (HR) and plasma epinephrine, norepinephrine, cortisol, ACTH, glucose, lac tate and fentanyl were analysed 15 min postinduction, 15 min poststernotomy , 15 min on CPB during cooling and during skin closure. Results: Mean BIS (SD) values for all 19 patients were 45.3 (12.3), 40.4 (1 4.5), 24.4 (12.4) and 47.9 (13.9), at the successive time points. No signif icant differences were observed in changes in BIS over time between the gro ups. A significant correlation was found 15 min postinduction between BIS a nd BP (systolic r=0.51, mean r=0.56) in all groups, but not between BIS and HR. BIS did not correlate with BP or HR at any other time point. There was no significant correlation between BIS and hormonal, biochemical or plasma fentanyl levels for any group at any time point. Conclusions: We were unable to demonstrate a relationship between the BIS a nd haemodynamic, metabolic or hormonal indices of anaesthetic depth. Furthe r evaluation of the BIS algorithm is required in neonates and infants.