Thorsten Michael Alves

Background Recently, entropy algorithms have been proposed as electroencephalographic measures of anesthetic drug effects. Datex-Ohmeda (Helsinki, Finland) introduced the Entropy Module, a new electroencephalographic monitor designed for measuring depth of anesthesia. The monitor calculates a state entropy (SE) computed over the frequency range of 0.8-32 Hz and a response entropy (RE) computed over the frequency range of 0.8-47 Hz. The authors investigated the dose-response relation of SE and RE during sevoflurane anesthesia in comparison with the Bispectral Index (BIS). Methods Sixteen patients were studied without surgical stimulus. Anesthesia was induced by sevoflurane inhalation with a tight-fitting facemask. Sevoflurane concentrations were increased and subsequently decreased and increased two to four times until the measurement was stopped and patients were intubated for surgery. The performances of SE, RE, and BIS to predict the estimated sevoflurane effect site concentration, obtained by simultaneous pharmacokinetic and pharmacodynamic modeling, were compared by calculating the correlation coefficients and the prediction probability. Results State entropy, RE, and BIS values decreased continuously over the observed concentration range of sevoflurane. Correlation coefficients were slightly but not significantly better for entropy parameters (0.87 +/- 0.09 and 0.86 +/- 0.10 for SE and RE, respectively) than for BIS (0.85 +/- 0.12). Calculating the prediction probability confirmed these results with a prediction probability of 0.84 +/- 0.05 and 0.82 +/- 0.06 for SE and RE, respectively, and 0.80 +/- 0.06 for BIS. Conclusion State entropy and RE seem to be useful electroencephalographic measures of sevoflurane drug effect.

Recently, Datex-Ohmeda introduced the Entropy Moduletrade mark for measuring depth of anesthesia. Based on the Shannon entropy of the electroencephalogram, state entropy (SE) and response entropy (RE) are computed. We investigated the dose-response relationship of SE and RE during propofol anesthesia in comparison with the Bispectral Indextrade mark (BIS). Twenty patients were studied without surgical stimulus. Anesthesia was induced by a constant propofol infusion of 2000 mg/h (451 +/- 77 microg x min(-1) x kg(-1)) via a large forearm vein. Propofol was infused until substantial burst suppression occurred (more than 50%) or mean arterial blood pressure decreased to <60 mm Hg. Hereafter, infusions were stopped until recovery of BIS values up to 60 was reached. Subsequently, the constant propofol infusion of 2000 mg/h was restarted to increase depth of anesthesia and again decreased (infusion was stopped) within the BIS value range of 40-60. The coefficient of determination (R2) and the prediction probability (P(K)) were calculated to evaluate the performance of SE, RE, and BIS to predict changing propofol effect-site concentrations. R2 values for SE, RE, and BIS of 0.88 +/- 0.08, 0.89 +/- 0.07, and 0.92 +/- 0.06, respectively, were similar. The calculated P(K) values, however, revealed a significant difference between SE and RE compared with BIS, with P(K) = 0.77 +/- 0.09, 0.76 +/- 0.10, and 0.84 +/- 0.06, respectively. BIS seems to show slight advantages in predicting propofol effect-site concentrations compared with SE and RE, as measured by P(K) but not as measured by R2.

In der vorliegenden Studie wurde das Dosisantwortverhalten der EEG-Parameter State- (SE) und Response Entropy (RE) im Vergleich zum Bispektral Index (BIS) bei wechselnden Propofolkonzentrationen untersucht.&lt;br /&gt;&lt;u&gt;Methodik:&lt;/u&gt; Entropie- und BIS-Werte wurden simultan in reiner Propofolnarkose ohne chirurgische Stimuli registriert, wobei die Narkosetiefe mehrfach nach Protokoll variiert wurde. Die resultierenden Dosis-Wirkungsverläufe (beobachteter EEG-Effekt in Abhängigkeit von der Propofolzufuhr) wurden dann mittels eines bi- bzw. mono- sigmoidalen Modell gefittet. Zur Beurteilung der Performance der Narkoseindices wurden anschließend das Bestimmtheitsmaß R² und die Vorhersagewahrscheinlich-keit PK berechnet.&lt;br /&gt;&lt;u&gt;Ergebnisse:&lt;/u&gt; Bei R² zeigten sich vergleichbar hohe Werte für beide Indices (BIS: 0,92 + 0,06; SE: 0,88 + 0,08; RE: 0,89 + 0,07), bei der Vorhersagewahrscheinlichkeit PK ergaben sich jedoch für den BIS (0,84 + 0,06) signifikant höhere Werte als für SE (0,77 + 0,09) und RE (0,76 + 0,10). &lt;br /&gt;&lt;u&gt;Beurteilung:&lt;/u&gt; Sowohl die Entropieparameter als auch der Bispektral Index scheinen gut zur Beurteilung der Narkosetiefe geeignet. Gemessen am PK-Wert gibt der BIS Änderungen der Propofol-Effektkompartmentkonzentration jedoch genauer wider.