Spectral entropy for assessing the depth of propofol sedation

Abstract

Background: For patients in the intensive care unit (ICU) or under monitored anesthetic care (MAC), the precise monitoring of sedation depth facilitates the optimization of dosage and prevents adverse complications from underor over-sedation. For this purpose, conventional subjective sedation scales, such as the Observer's Assessment of Alertness/Sedation (OAA/S) or the Ramsay scale, have been widely utilized. Current procedures frequently disturb the patient's comfort and compromise the already well-established sedation. Therefore, reliable objective sedation scales that do not cause disturbances would be beneficial. We aimed to determine whether spectral entropy can be used as a sedation monitor as well as determine its ability to discriminate all levels of propofol-induced sedation during gradual increments of propofol dosage.

Methods: In 25 healthy volunteers undergoing general anesthesia, the values of response entropy (RE) and state entropy (SE) corresponding to each OAA/S (5 to 1) were determined. The scores were then analyzed during each 0.5 mcg/ml- incremental increase of a propofol dose.

Results: We observed a reduction of both RE and SE values that correlated with the OAA/S (correlation coefficient of 0.819 in RE-OAA/S and 0.753 in SE-OAA/S). The RE and SE values corresponding to awake (OAA/S score 5), light sedation (OAA/S 3-4) and deep sedation (OAA/S 1-2) displayed differences (P < 0.05).

Conclusions: The results indicate that spectral entropy can be utilized as a reliable objective monitor to determine the depth of propofol-induced sedation.

Keywords: Entropy; Propofol; Sedation.

Fig. 1

Response entropy (A) and state entropy (B) values corresponding to each of the observer's assessment of alertness/sedation (oaa/s) score. The values of both RE and SE displayed a significant correlation with the OAA/S scores (r = 0.811, r² = 0.657, y = 17.987 + 15.653 x) and (r = 0.802, r² = 0.644, y = 16.1 + 14.4 x), respectively.

Fig. 2

Response entropy (A) and state entropy (B) during various sedation levels. Each sedation group differed from the others by all pair-wise multiple comparison procedures (Dunn's method [P < 0.005]).