Brain tumors may alter the relationship between bispectral index values and propofol concentrations during induction of anesthesia

Study ObjectiveTo compare propofol-predicted effect-site concentrations (PropCe) and bispectral index (BIS) of the electroencephalogram during induction of anesthesia in patients with small brain tumors and to analyze BIS and PropCe at loss of consciousness (LOC).DesignProspective investigation.SettingOperating theater of a university hospital.Patients26 ASA physical status I and II patients, 13 of whom were scheduled for nontumor spinal surgeries, and the other 13, for brain surgery for small brain tumor removal.InterventionsAnesthesia was induced with a propofol 1% constant infusion rate of 200 mL/h until LOC.MeasurementsBIS, PropCe, heart rate, and mean arterial pressure were analyzed at the beginning of the propofol infusion and every 30 seconds during induction.Main ResultsThe BIS values were significantly higher in patients with brain tumors in the period from 150 to 210 seconds, with PropCe similar to patients without brain tumors. Loss of consciousness occurred 3.6 ± 0.8 minutes in patients without brain tumors and 3.9 ± 0.7 minutes in patients with brain tumors. No differences were observed between groups in the time to LOC (3.6 ± 0.8 in group 1 vs 3.9 ± 0.7 in group 2) or in BIS at LOC (48.7 ± 11.4 in group 1 vs 58.6 ± 21.7 in group 2).ConclusionsFor similar propofol concentrations, patients with small brain tumors show higher BIS values on induction of anesthesia with propofol.