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

STUDY OBJECTIVE: To 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). DESIGN: Prospective investigation. SETTING: Operating theater of a university hospital. PATIENTS: 26 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. INTERVENTIONS: Anesthesia was induced with a propofol 1% constant infusion rate of 200 mL/h until LOC. MEASUREMENTS: BIS, PropCe, heart rate, and mean arterial pressure were analyzed at the beginning of the propofol infusion and every 30 seconds during induction. MAIN RESULTS: The 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). CONCLUSIONS: For similar propofol concentrations, patients with small brain tumors show higher BIS values on induction of anesthesia with propofol.