BIS vs Entropy

Started by Ahmad Menari, December 24, 2004, 01:48:15 AM

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Ahmad Menari

I have been a user of the Bispectral Index (BIS) monitor for about 6 months now, and find it a useful adjunct to gauging anesthetic depth.

I recently moved to a new hospital which did not have BIS monitoring, but did have Datex Entropy monitors, which for all intents and purposes looks and behaves like the BIS.

I am wondering if anyone else has had experience with both BIS and Entropy and how they compare in practice. I have found the following article that gives some comparison, but I am interested in "real-world" experiences.

QuoteTime-frequency balanced spectral entropy as a measure of anesthetic drug effect in central nervous system during sevoflurane, propofol, and thiopental anesthesia.
Vakkuri A, Yli-Hankala A, Talja P, Mustola S, Tolvanen-Laakso H, Sampson T, Viertio-Oja H.

Acta Anaesthesiol Scand. 2004 Feb;48(2):145-53. (PDF: 376KB)


Time-frequency balanced spectral entropy of electroencephalogram (EEG) and frontal electromyogram (FEMG) is a novel measure of hypnosis during anesthesia. Two Entropy parameters are described: Response entropy (RE) is calculated from EEG and FEMG; and State Entropy (SE) is calculated mainly from EEG. This study was performed to validate their performance during transition from consciousness to unconsciousness under different anesthetic agents.

METHODS: Response entropy, SE [S/5 Entropy Module, M-ENTROPY (later in text: Entropy), Datex-Ohmeda Division, Instrumentarium Corp., Helsinki, Finland] and BIS (BIS XP, A-2000, Aspect Medical Systems, Newton, MA) data were collected from 70 patients; 30 anesthetized with propofol 2 mg kg-1, 20 with sevoflurane inhalation, and 20 with thiopental 5 mg kg-1. Loss and regaining of consciousness (LOC, ROC) was tested every 10 s, and sensitivity, specificity, and prediction probability (Pk) were calculated. Behavior of the indices was studied.

RESULTS: Sensitivity, specificity, and Pk values for consciousness were high and similar for all indices. During regaining of consciousness after propofol bolus, RE, SE, and BIS values recovered by 81 +/- 22%, 75 +/- 26%, and 59 +/- 18% (mean +/- SD), respectively, from the minimum relative to their baseline. After thiopental bolus, RE, SE, and BIS values recovered by 86+/-21%, 88 +/- 13%, and 63 +/- 14%, respectively. The relative rise was higher in RE and SE compared with BIS (P < 0.01). During deep levels of hypnosis, RE and SE decreased monotonously as a function of burst suppression ratio, while BIS showed biphasic behavior. On average, RE indicated emergence from anesthesia 11 s earlier than SE, and 12.4 s earlier than BIS.

CONCLUSIONS: All indices, RE, SE, and BIS, distinguished excellently between conscious and unconscious states during propofol, sevoflurane, and thiopental anesthesia. During burst suppression, Entropy parameters RE and SE, but not BIS, behave monotonously. During regaining of consciousness after a thiopental or propofol bolus, RE and SE values recovered significantly closer to their baseline values than did BIS. Response entropy indicates emergence from anesthesia earlier than SE or BIS

Michael de Sousa

Datex Entropy module seems to correlate well with the BIS readings. I found this abstract:

QuoteAnesthesiology. 2004 Dec;101(6):1283-90.

Comparative evaluation of the Datex-Ohmeda S/5 Entropy Module and the Bispectral Index monitor during propofol-remifentanil anesthesia.

Schmidt GN, Bischoff P, Standl T, Hellstern A, Teuber O, Schulte Esch J.

Department of Anesthesiology, University Hospital Hamburg-Eppendorf, Hamburg, Germany.

BACKGROUND: Different analytical concepts were introduced to quantify the changes of the electroencephalogram. The Datex-Ohmeda S/5 Entropy Module (Datex-Ohmeda Division, Instrumentarium Corp., Helsinki, Finland) was the first commercial monitor based on the entropy generating two indices, the state entropy (SE) and the response entropy (RE). The aim of the current study was to compare the accuracy of SE and RE with the Bispectral Index(R) monitor (BIS(R); Aspect Medical Systems, Newton, MA) during propofol-remifentanil anesthesia. METHODS: The authors investigated 20 female patients during minor gynecologic surgery. SE, RE, BIS, mean arterial blood pressure, heart rate, and sedation level were recorded every 20 s during stepwise increase (target-controlled infusion, 0.5 microg/ml) of propofol until the patients lost response. Five minutes after loss of response, remifentanil infusion (0.4 microg . kg(-1) . min(-1)) was started. Spearman correlation coefficient and prediction probability were calculated for sedation levels with SE, RE, BIS, mean arterial blood pressure, and heart rate. The ability of the investigated parameters to distinguish between the anesthesia steps awake versus loss of response, awake versus anesthesia, anesthesia versus first reaction, and anesthesia versus extubation was analyzed with the prediction probability. RESULTS: SE correlates best with sedation levels, but no significant differences of the prediction probability values among SE, RE, and BIS were found. The prediction probability for all investigated steps of anesthesia did not show significant differences among SE, RE, and BIS. SE, RE, and BIS were superior to mean arterial blood pressure and heart rate. CONCLUSION: SE, RE, and BIS revealed similar information about the level of sedation and allowed the authors to distinguish between different steps of anesthesia. Both monitors provided useful additional information for the anesthesiologist.

George Miklos

Both the BIS and the Datex Entropy monitors have been closely correlated with the likelihood of both explicit and implicit recall. The actual numbers I am not experienced enough to comment on.

Of course, this leads into a discussion of consciousness, sedation and anesthesia..... the subject of a new topic I suspect!

Walter Petorski

I have used BIS for over 3 years now and have a lot of experience with it. The Entropy monitor was introduced on a trial basis in our department just a efw months ago, so I have less experience with it.

I have found both monitors fairly redundant when using volatile anesthesia. They add nothing new to my clinical assessment of the patients depth of anesthesia as well as my end-tidal volatile reading. Where I do find it useful is in propofol infusion anesthesia. I think patients' propofol requriements vary enourmously and we cannot rely on the theoretical value given by the infusion pump when using TIVA. In this situation, I find both the BIS and Entropy useful - mainly in that they allow me to drop my target levels significantly while still maintaining a degree of confidence of lack of awareness. My patients then wake up quicker and cleaner at the end.

As for differences between the two monitors - not much between the two.


The company blurb for the Datex Entropy monitor states that it has a faster response time than the BIS - it reacts to a lightened level of anesthesia within 3 seconds rather than the 30 seconds stated for the BIS. This would make it far more useful as a tool to prevent awareness as you may miss the boat with the BIS.