• Anesthesia and analgesia · Aug 2003

    The bispectral index declines during neuromuscular block in fully awake persons.

    Using an Aspect A-1000 BIS monitor, researchers demonstrated a drop in Bispectral Index Score in awake, paralysed volunteers to low values ranging from 9 to 64.

    pearl
    • M Messner, U Beese, J Romstöck, M Dinkel, and K Tschaikowsky.
    • Department of Anesthesiology, Friedrich-Alexander Universität, Erlangen-Nuernberg, Germany. messner@gmx.li
    • Anesth. Analg.. 2003 Aug 1;97(2):488-91, table of contents.

    UnlabelledBispectral index (BIS) is an electroencephalographic variable promoted for measuring depth of anesthesia. Electromyographic activity influences surface electroencephalography and the calculation of BIS. In this study, we sought to determine the effect of spontaneous electromyographic activity on BIS. BIS was monitored in three volunteers by using an Aspect A-1000 monitor. The experiment was repeated in one volunteer. Electromyographic activity was recorded. Alcuronium and succinylcholine were administered. No other drugs were used. In parallel with spontaneous electromyographic activity of the facial muscles, BIS decreased in response to muscle relaxation to a minimum value of 33 and, in the repeated measurement, to a minimum value of 9 when total neuromuscular block was achieved. In two volunteers, no total block was achieved. BIS decreased to a minimal value of 64 and 57, respectively. In turn, recovery of BIS coincided with the reappearance of spontaneous electromyographic activity. During the entire experiment, the volunteers had full consciousness. BIS, assessed by software Version 3.31, correlates with spontaneous electromyographic activity of the facial muscles. BIS failed to detect awareness in completely paralyzed subjects. Thus, in paralyzed patients, BIS monitoring may not reliably indicate a decline in sedation and imminent awareness.ImplicationsThe bispectral index (BIS) is an electroencephalographic variable intended for measuring depth of anesthesia. Electromyographic activity influences the calculation of BIS. We found that the administration of a muscle relaxant to unanesthetized volunteers decreases the bispectral index value. Thus, awareness in totally paralyzed patients cannot be excluded.

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    This article appears in the collections: General Stuff and Neuromuscular myths: the lies we tell ourselves.

    Notes

    pearl
    1

    Using an Aspect A-1000 BIS monitor, researchers demonstrated a drop in Bispectral Index Score in awake, paralysed volunteers to low values ranging from 9 to 64.

    Daniel Jolley  Daniel Jolley
     
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