Objectives: To determine the bispectral (BIS) index during induction of sedation with sevoflurane and awakening in children undergoing magnetic resonance imaging (MRI).
Material and methods: We studied 50 pediatric patients sedated only with 2% sevoflurane in oxygen and air administered through a face mask. BIS was monitored during induction, before MRI, after MRI, during awakening, upon first movement, and upon eye opening or first cry.
Results: The scan was performed successfully in all patients (none moved during the procedure) even though there was great variability in BIS indices (before MRI, 59.5 [SD, 11.1]; after MRI, 52.8 [13.7]). BIS indices before and after MRI were correlated, although the index after MRI was significantly lower than the index before the scan (P<0.01), indicating that hypnosis became deeper during the procedure. The first spontaneous movement and crying or eye opening produced significantly higher BIS indices (P<0.01) (movement, 75.4 [15.9]; crying, 79.8 [15.6]), although variation was also greater. The BIS index did not exceed 70 for 15 patients (31.3%) upon eye opening and for 12 (27.3%) at the first cry. Children under 6 months of age had significantly lower BIS indices before and after MRI scans than did the older children (P<0.01).
Conclusions: In the absence of painful stimuli, the BIS index reflects the patient's level of hypnosis but does not predict recovery of consciousness.