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 97.2 ± 1.1; when the OAA/S was 4, mean BIS was 84.3 ± 4.6 and mean propofol effect site concentration was 0.8 ± 0.3µgram/ml; when the OAA/S was 3, mean BIS was 78.4 ± 4.3 and mean propofol effect site concentration was 1.2 ± 0.3µgram/ml; and when the OAA/S was 2, mean BIS was 73.2 ± 5.9 and mean propofol effect site concentration was 1.5 ± 0.4µgram/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.