Spectral entropy as an objective measure of sedation state in midazolam-premedicated patients

Abstract

Context: Objective assessment of sedation depth is a valuable target. Spectral entropy is an anesthetic depth monitor based on the analysis of the electroencephalogram signal.

Aims: To evaluate the performance of spectral entropy as an objective measure of sedation state in midazolam-premedicated patients and to correlate it with a clinically assessed sedation score.

Settings and design: This prospective double-blind placebo-controlled study was performed in King Fahd Hospital of the university.

Methods: Eighty adult ASA I-II patients were randomly assigned into 4 groups. Patients were premedicated using 0.02, 0.04, or 0.06 mg/kg midazolam or saline intramuscularly. The effect of these doses on the Observer's Assessment of Alertness and Sedation (OAA/S) scale, hemodynamic variables, response entropy (RE), and state entropy (SE), was evaluated at 10, 20, and 30 min after premedication.

Statistical analysis: Spearman Rank-order correlation analysis to examine the relation between OAA/S and entropy. The ability of spectral entropy to predict the depth of sedation was evaluated using Smith prediction probability.

Results: Midazolam doses ≥0.04 mg/kg produced significant decreases in RE, SE, and OAA/S scores. There was a strong correlation between midazolam dose and OAA/S scale, RE, and SE since Spearman Rank R values were 0.792, 0.822, and 0.745, respectively (P<0.001). In addition, RE and SE were strong predictors of OAA/S level during midazolam sedation with no significant difference in prediction between the 2 entropy components.

Conclusions: Spectral entropy is a reliable measure for the sedative premedication. It may be used to objectively assess the adequacy of midazolam premedication and to determine the dose requirement.

Keywords: Monitoring; depth of anaesthesia; midazolam; observer's assessment of alertness and sedation; premedication; sedation.

Figure 1

Box plot graphic of response entropy (RE) and state entropy (SE) represented on the left Y axis, and Observer's Assessment of Alertness/Sedation (OAA/S) Scale scores represented on the right Y axis at different midazolam doses in mg/kg. Data points represent medians, boxes are interquartile ranges, and whiskers are nonoutlier ranges. ^*Significant difference in comparison with 0 mg/kg; #significant difference in comparison with 0.02 mg/kg