TITLE: BIS MONITORING IN INFANTS UNDERGOING CARDIOPULMONARY BYPASS

AUTHORS: Barry D. Kussman, MBBCh, Eva M. Gruber, MD, Dolly D. Hansen, MD, David Zurakowski, PhD, Alfonso Casta, MD, Peter C. Laussen, MBBS
AFFILIATION: Children's Hospital, Boston, MA.

INTRODUCTION: Hemodynamic and biochemical changes may be used to assess depth of anesthesia (1). Bispectral index (BIS), a measure of depth of anesthesia, has not been evaluated in infants. The potential for awareness is increased during cardiac surgery (2), and the purpose of this study was to determine the correlation between BIS and hemodynamic changes and bio- chemical markers of the stress response during pediatric cardiac surgery.
METHODS: With IRB approval and parental informed consent, BIS monitoring (Aspect Medical Systems, Natick MA) was used in 19 of 45 infants undergoing cardiac surgery who had been enrolled in a prospective, randomized, blinded study to determine whether midazolam combined with high dose opiod anesthesia blunted the stress response more than high dose opiod anesthesia alone. Group 1 (n=8) received high dose fentanyl by bolus technique. Group 2 (n=6) received high dose fentanyl by continuous infusion. Group 3 (n=5) received a fentanyl- midazolam infusion. Blood pressure (BP), heart rate (HR), and plasma epinephrine, norepinephrine, cortisol, ACTH, glucose and lactate were analysed 15 minutes post-induction, 15 minutes post-sternotomy, 15 minutes on CPB during cooling, and during skin closure. BIS electrodes (Zipprep, Aspect Medical Systems, Natick MA) were placed following induction. Repeated measures ANOVA were used to assess differences in BIS over time and between groups. Correlations were measured by Pearson's coefficient (r). Data are expressed as mean (SD) and significance using two-tailed p < 0.05.
RESULTS: Mean age was 3.5 (1.5) months and mean weight 4.7 (1.3) kg. BIS values (n=19) were 45.3 (12.3), 40.4 (14.5), 24.4 (12.4) and 47.9 (13.9) at the successive time points, with no significant difference between groups. A significant correlation was found 15 minutes post-induction between BIS and BP (systolic r = 0.51, diastolic r = 0.47, 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 correlation between BIS and any biochemical marker at any time point.
DISCUSSION: Awareness is difficult to assess in infants. This study only demonstrated a positive correlation between BIS and BP shortly after induction. The validity of BIS in pediatric cardiac surgery needs further evaluation, particularly as the EEG descriptors and corresponding clinical states in the BIS database are derived from adult populations.
REFERENCES:

(1)Br J Anaesth 59, 1341, 1987.

(2)Anaesthesia 42, 596, 1987