Article

Entropy indices vs the bispectral index (TM) for estimating nociception during sevoflurane anaesthesia

Tokyo Women's Medical University, Edo, Tōkyō, Japan
BJA British Journal of Anaesthesia (Impact Factor: 4.35). 06/2006; 96(5):620-6. DOI: 10.1093/bja/ael050
Source: PubMed

ABSTRACT It is now possible to acquire and process raw EEG and frontal EMG signals to produce two spectral-entropy-based indices (response entropy and state entropy) reflective of analgesic and hypnotic levels during general anaesthesia (with the Datex-Ohmeda S/5 Entropy Module, Datex-Ohmeda, Helsinki, Finland). However, there are no data available on the accuracy of the Entropy Module in estimating nociception during sevoflurane anaesthesia.
Forty female patients were enrolled in the present study. Each patient was allocated randomly to one of four end-tidal sevoflurane concentration (ET(sev)) groups (1.3, 1.7, 2.1 or 2.5%). A BIS Sensor (Aspect Medical Systems, Newton, MA) and an Entropy Sensor (Datex-Ohmeda) were applied side-by-side to the forehead. The bispectral index (A-2000 BIS Monitor, version 3.4, Aspect Medical Systems), response entropy, state entropy and patient movement were observed after electrical stimulation (20, 40, 60 and 80 mA, 100 Hz, 5 s) and after skin incision during sevoflurane anaesthesia (1.3, 1.7, 2.1 or 2.5%). Accuracy of the EEG variables in differentiating the intensity of electrical stimulation was estimated by the prediction probability (P(K)) values.
Response entropy and state entropy [median, (range)] before skin incision were significantly lower in patients who did not move [29 (15-41) and 24 (14-41)] than in those that did [38 (24-53) and 37 (24-52)], but there was no significant difference in BIS. All EEG variables increased significantly (P<0.0001 for all) with increases in the intensity of electrical stimulation. The difference between response entropy and state entropy increased with increases in the electrical stimulation (P<0.0001). However, no EEG variables could differentiate the intensity of the electrical stimulations accurately because of low P(K)-values (P(K)<0.8).
Noxious stimulation increased the difference between response entropy and state entropy. However, an increase in the difference does not always indicate inadequate analgesia and should be interpreted carefully during anaesthesia.

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    • "Clinical endpoints, such as movement in response to nociceptive stimulation, are commonly used as an indicator of inadequate analgesia [23] but are also unreliable and suppressed by muscle relaxants [24]. Some electroencephalographic (EEG-) derived variables, such as Entropy, especially the difference between state entropy (SE) and response entropy (RE), are proposed to be useful for evaluating the nociceptive component of anaesthesia [17] [25] [26]. Additionally, changes in skin conductivity and photoplethysmographic pulse wave amplitude or pulse wave reflex have been suggested as indicators of stress or nociception [27] [28]. "
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    • "In some studies, noxious pain like tracheal intubation increases spectral entropy, especially RE rather than BIS [12,13], since noxious pain is relevant to increases EMG activity [14]. By comparison, we investigated BIS, RE and SE values during induction of anesthesia, and not in anesthetized patients. "
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    • "Clinical endpoints , such as movement reaction in response to nociceptive stimulus, can be used as an indicator of inadequate analgesia [2], but it is not very useful during operation when patients are paralysed. Some electroencephalographic (EEG)-derived parameters, such as Entropy, are suggested to reflect also the nociceptive component of anesthesia [3] [4] [5]. Changes in skin conductivity and suppression of photoplethysmographic pulse wave amplitude (PPWA) have also been proposed as indicators of nociception [6] [7]. "
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