Entropy monitoring

Entropy monitoring is a method of assessing anaesthetic depth. It was commercially developed by Datex-Ohmeda, which is now part of GE Healthcare.

The Entropy system captures a single-lead frontal EEG via a 3-electrode sensore applied to the pateint's forehead. The system relies on a method of assessing the degree of irregularity in electroencephalogram (EEG) signals. The principle is that the irregularity of an EEG signal decreases with increasing brain levels of anaesthetic drugs and that the entropy is a measure of that irregularity.

Entropy monitors generate two numbers that are derived from different to frequency bands used. The State Entropy (SE) is calculated from the 0.8Hz to 32Hz range, whereas the Response Entropy (RE) uses frequencies up to 47Hz. Electromyogram activity is more predominant in those higher frequencies, and so Response Entropy respond more quickly, when muscle activity is present.

Published studies show that Entropy values do relate to clinical levels of anaesthetic depth. Most of the commonly-used anaesthetic drugs are detectable by Entropy monitoring, a notable exception being nitrous oxide, in common with BIS monitoring.

Other vital signs such as pulse, heart rate, blood pressure, and movement are indirect indicators of consciousness, but are unreliable. When these are combined with expired gas analysis of inhalational anaesthetic agents, an experienced anaesthetist can be confident a patient is unconscious and not aware of their surroundings. However, the direct measurement of brain activity using a basic EEG is purported to measure effects of anaesthetics more comprehensively. Unlike the Bispectral Index monitor, the algorithm of the Entropy monitor has been fully disclosed.

See also

• bispectral index
• evoked potentials

References

• Viertio-Oja, H.; Maja, V.; Sarkela, M.; Talja, P.; Tenkanen, N.; Tolvanen-Laakso, H.; Paloheimo, M.; Vakkuri, A.; Yli-Hankala, A. (2004-02). "Description of the Entropy (TM) algorithm as applied in the Datex-Ohmeda S/5 (TM) Entropy Module". Acta Anaesthesiologica Scandinavica. 48 (2): 154–161. doi:10.1111/j.0001-5172.2004.00322.x. ISSN 0001-5172. {{cite journal}}: Check date values in: |date= (help)
• Bein B (2006). "Entropy". Best practice&research clinical anesthesiology. 20 (1): 101–109. doi:10.1016/j.bpa.2005.07.009.
• Gao JD, Zhao YJ, Xu CS, Zhao J, Huang YG, Wang TL, Pei L, Wang J, Yao LN, Ding Q, Tan ZM, Zhu ZR, Yue Y (Apr 2012). "Evaluation of entropy for monitoring the depth of anesthesia compared with bispectral index: a multicenter clinical trial". Chin Med J (Engl). 125 (8): 1389–92. PMID 22613640.
• Schmidt GN, Bischoff P, Standl T, Hellstern A, Teuber O, Schulte Esch J (Dec 2004). "Comparative evaluation of the Datex-Ohmeda S/5 Entropy Module and the Bispectral Index monitor during propofol-remifentanil anesthesia. Anesthesiology". 101 (6): 1283–90. PMID 15564934. {{cite journal}}: Cite journal requires |journal= (help)