[Entropy: a new method of measuring depth of anesthesia. Comparative study with bispectral index during clinical evaluation in tracheal intubation of patients anesthetized with sevoflurane.].
OBJECTIVE
Spectral entropy, a new EEG analysis method based on the quantification of EEG chaos, was developed to monitor anesthetic depth. The spectral entropy involves two distinct types of analysis: state entropy (SE), which includes low frequency signals (< 32 Hz), and response entropy (RE), which includes signals up to 47 Hz. This study aimed at comparing entropy-derived values to BIS-derived values and sub-cortical (autonomic and somatic) responses recorded during tracheal intubation in patients submitted to general anesthesia with sevoflurane.


METHODS
Participated in this study 36 patients ASA I, aged 20 to 44 years, assigned to four groups (G1-G4) of nine patients submitted to tracheal intubation (TI). In all groups anesthesia was induced with sevoflurane, associated or not to fentanyl, according to the following regimens: G1 = sevoflurane plus 2.5 microg.kg-1 fentanyl; G2 = sevoflurane plus 5 microg.kg-1 fentanyl; G3 = sevoflurane plus 7.5 microg.kg-1 fentanyl; and G4 = sevoflurane plus saline solution. The following parameters were monitored: SBP, DBP, HR, BIS, SE, RE, sevoflurane expired concentration (EC) and motor response to TI at three moments: M1 = immediately before induction; M2 = immediately before tracheal intubation and M3 = one minute after tracheal intubation.


RESULTS
BIS and SE values have linearly varied in all groups, with significant differences between M2 and M3 for Groups 1 and 4. At M3, BIS and SE values in G4 were above those for the threshold between consciousness and unconsciousness. Hemodynamic changes were not clinically significant, with the exception of HR increase between M1 and M3 for G4 (p < 0.05%). In G1, 66% of patients have reacted to TI maneuvers as compared to 100% in G4.


CONCLUSIONS
Our findings suggest that sevoflurane alone or in association with 2.5 microg.kg-1 or 5 microg.kg-1 fentanyl does not effectively block CNS cortical and subcortical components responses during tracheal intubation, being sevoflurane plus 7.5 microg.kg-1 fentanyl the best association to control anesthetic components.
Nunes
Rogean Rodrigues
RR
Serviço de Anestesiologia, Hospital São Lucas.