The differences in the bispectral index between infants and children during emergence from anesthesia after circumcision surgery

The bispectral index (BIS) correlates with consciousness during adult anest hesia. In this prospective, blinded study of children (n = 24) and infants (n = 25) undergoing elective circumcision, we evaluated BIS and consciousne ss level during emergence from anesthesia. Anesthesia was maintained with s evoflurane, and a penile nerve block was performed in each patient before s urgical stimulation. At the completion of surgery, the sevoflurane was decr eased stepwise from 0.9% in increments of 0.2%, and arousal was tested with a uniform auditory stimulus given after a steady state of end-tidal sevofl urane concentration was achieved at each step. The BIS increased significan tly as the sevoflurane concentrations decreased in children (0.9%,62.5 +/- 8.1; 0.7%,70.8 +/- 7.4; and 0.5%, 74.1 +/- 7.1; P < 0.001 for 0.7% and 0.5% compared with 0.9%), but a similar relationship was not demonstrated in in fants. The BIS values at 0.7% and 0.5% sevoflurane were significantly highe r in children than infants (P < 0.02 and P < 0.002, respectively). In both children and infants, the BIS increased significantly from pre- to postarou sal (children, 73.5 +/- 7 to 83.1 +/- 12, P = 0.01; infants, 67.8 +/- 10 to 85.6 +/- 13.6, P < 0.001). The BIS at which arousal was possible with the stimulus tended to be higher in children than in infants (P = 0.06).