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ANESTHETIC PHARMACOLOGY

Muscle Relaxation Does Not Alter Hypnotic Level During Propofol Anesthesia

Robert Greif, MD^*, Scott Greenwald, PhD, Ekkehard Schweitzer, MD, Sonja Laciny, MD^*, Angela Rajek, MD, James E. Caldwell, MB ChB^||, and Daniel I. Sessler, MD^¶

*Department of Anesthesiology and Intensive Care Medicine, Donauspital-SMZO, Vienna, Austria; Director of Research, Aspect Medical Systems, Inc., Newton, Massachussetts; Department of Anesthesia and Intensive Care, Krankenhaus Lainz; Ludwig Boltzmann Institute for Economics of Medicine in Anesthesia and Intensive Care, Vienna, Austria; Department of Cardiothoracic and Vascular Anesthesia, University of Vienna, Vienna, Austria; ||Department of Anesthesia and Perioperative Care, University of California—San Francisco, San Francisco, California, and ¶Outcomes Research Institute, University of Louisville, Louisville, Kentucky and Ludwig Boltzmann Institute, University of Vienna, Vienna, Austria

Address correspondence to Daniel I. Sessler, MD, University of Louisville, Abell Administration Center, Room 217, 323 East Chestnut Street, Louisville, KY 40202-3866. Address e-mail to sessler{at}louisville.edu

Electromyographic (EMG) activity can contaminate electroencephalographic signals. Paralysis may therefore reduce the Bispectral Index (BIS) by alleviating artifact from muscles lying near the electrodes. Paralysis may also reduce signals from muscle stretch receptors that normally contribute to arousal. We therefore tested the hypothesis that nondepolarizing neuromuscular block reduces BIS. Ten volunteers were anesthetized with propofol at a target effect site concentration of 3.8 ± 0.4 µg/mL. A mivacurium infusion was adjusted to vary the first twitch (T1) in a train-of-four to 80%, 30%, 20%, 15%, 10%, 5%, or 2% of the prerelaxant intensity. At each randomly assigned T1, we measured BIS and frontal-temporal EMG intensity. BIS averaged 95 ± 4 before induction of anesthesia, and decreased significantly to 40 ± 5 after propofol administration. However, there were no significant differences at the designated block levels. Frontal-temporal EMG intensity averaged 47 ± 3 dB before induction of anesthesia, and decreased significantly to 27 ± 1 dB after propofol administration. However, there were no significant differences at the designated block levels. These data suggest that the BIS level and EMG tone are unaltered by mivacurium administration during propofol anesthesia.

IMPLICATIONS: Neuromuscular block level did not alter Bispectral Index (BIS) during propofol anesthesia, either by reducing electromyographic artifact or by decreasing afferent neuronal input. The BIS will thus comparably estimate sedation in deeply unconscious patients who are paralyzed, partially paralyzed, or unparalyzed.

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999