State entropy and bispectral index: correlation with end tidal sevoflurane concentrations

Aim of this study was to evaluate the difference between the correlations of state entropy (SE) and bispectral index (BIS) with different end tidal concentrations (Et) of sevoflurane.

A total of 40 ASA I/II patients submitted to abdominal surgery were enrolled in the study. After premedication with fentanyl, anesthesia was induced with propofol and atracurium and maintained with sevoflurane in oxygen and air. The values of Et sevoflurane, SE and BIS were recorded during the operating room stay. The mean Et sevoflurane was calculated and the correlations of SE and BIS with Et sevoflurane were determined with Pearson test separately at values of Et sevoflurane below and higher the mean Et sevoflurane. Student's t-test was used to verify if the difference between the correlations was significant (P<0.05).

The mean Et sevoflurane was 1.5%. During anesthesia the correlation with Et sevoflurane was -0.75 for SE and -0.70 for BIS. At Et sevoflurane higher than 1.5% the correlation with Et sevoflurane was -0.41 for SE and -0.14 for BIS. At Et sevoflurane below 1.5% the correlation with Et sevoflurane was -0.65 for SE, and -0.8 for BIS. The difference between the correlations of Et sevoflurane with SE and BIS resulted statistically significant.

During sevoflurane anesthesia SE shows a better correlation than BIS with Et sevoflurane. Although at low Et sevoflurane the correlation is better with BIS, at high Et sevoflurane the correlation is better with SE.