BACKGROUND: The bispectral index (BIS) is a processed EEG information that has been validated as a means to measure the hypnotic effect of anesthetic drugs. The aim of this study was to evaluate the BIS changes during anesthesia induction with ketamine in children.

METHODS: Eighty-four ASA class I and II pediatric patients, aged 3-8 years, were enrolled in this study. In each patient the BIS value was recorded before anesthesia induction. Without premedication, eighty-four patients received ketamine bolus, 1.0 mg/kg (Group 1, n = 28) or 1.5 mg/kg (Group 2, n = 28) or 2.0 mg/kg (Group 3, n = 28). When unresponsiveness to verbal commands (UVC) and loss of eyelash reflex (LER) were ascertained, intubation was performed after administration of succinylcholine 1.5 mg/kg and anesthesia was maintained with 2.0% enflurane and 50% N₂O-50% O₂.

RESULTS: Ketamine bolus induced UVC and LER at which the BIS values were, 92.5±5.6 and 93.9±3.0 for Group 1, 92.5±6.3 and 92.6±4.4 for Group 2, and 93.0±4.3 and 91.0±4.1 for Group 3. BIS from UVC and LER to three minutes after ketamine bolus remained above 90 for Group 1 and 2, whereas lower than Group 1 for Group 3 (P<0.05). However, the BIS for Group 3 showed above 85 as patient entered into clinical anesthetic state.

CONCLUSIONS: Our study showed that there is a lack of correlation between the BIS and the anesthetic state induced by ketamine in children aged 3-8 years. Monitoring the depth of ketamine anesthesia remains difficulty.