Correlations between the Modified Observer's Assessment of Alertness/Sedation Scale, Bispectral Index and Propofol Effect Site Concentrations in Sedated Elderly Patients under Regional Anesthesia

Abstract

Background: To maintain an adequate sedation level in elderly patients (over 65 years) under regional anesthesia, we evaluated the correlations between the modified observer's assessment of alertness/sedation (OAA/S) scale, bispectral index (BIS), propofol effect site concentrations. Methods: In elderly patients (over 65 years) scheduled for transurethral resection of a bladder tumor or prostate, we measured BISs and started propofol infusion using the target controlled infusion (TCI) method to sedate patients after regional anesthesia. OAA/S composite scores, measured BISs propofol effect site concentrations and vital signs were determined. Results: When the OAA/S composite score was 5, mean BIS was 97.21.1; when the OAA/S was 4, mean BIS was 84.34.6 and mean propofol effect site concentration was 0.80.3/ml; when the OAA/S was 3, mean BIS was 78.44.3 and mean propofol effect site concentration was 1.2 0.3/ml; and when the OAA/S was 2, mean BIS was 73.25.9 and mean propofol effect site concentration was 1.5 0.4/ml. The OAA/S scale was found to be well correlated with BIS (Pearson's r = 0.973) and the propofol effect site concentration (Pearsons's r = 0.968). BIS was also well correlated with propofol effect site concentration (Pearson's r = 1.0). Conclusions: BIS was found to be a good tool for monitoring sedation level in elderly patients under regional anesthesia with propofol sedation.