A cerebral pharmacodynamic feedback may help the anesthesiologist to adjust anesthetics administration. The BIS, which provides a single number resulting from an algorithm calculated from cortical EEG parameters, may play this role.Moreover, halogenated agents and propofol may have different EEG effects, which might interfere on measured BIS values.

The aim of this prospective randomized study was to compare, in steady state conditions, the EEG profiles in children anesthetized with sevoflurane (S) or propofol (P) : for both anesthetics, the BIS-concentration relationship and raw EEG were analysed at different levels of general anesthesia.

Children will be prospectively included and randomly assigned in two groups : Propofol (P) Group or Sevoflurane (S) Group.

Steady state periods will be performed at a fixed randomized concentration between 2, 3, 4, 5 and 6 mcg/ml of stable Ct P concentration in the P group and between 1,2,3,4,5 % of FeS in the S group.

At the end of each steady-state period the BIS value was noted and the relationship between BIS and anesthetic concentrations will be studied using non linear regression. For all steady state periods, EEG traces will be reviewed to determine the presence of epileptiform signs (ES) and spectral EEG signal analysis with fast Fourier transformation (FFT) will be performed.

Inclusion Criteria:

• from five to eighteen year of age, ASA 1 or 2, scheduled for middle ear surgery

Exclusion Criteria:

• obesity (body mass index > percentile 97); history of cardiac, pulmonary, or renal disease; known neurological or neuromuscular disorders; preoperative administration of medications known to interfere with the central nervous system