Letters to the Editor: Letters & Announcements
We appreciate the opportunity to respond to Dr. White and thank him for the continuing interest in our work.
As Dr. White stated in his letter, our study confirmed an effect of electromyographic activity on the bispectral index as previously reported (1) but led to different results and conclusions.
Bruhn et al. (2) reported two cases of unexpected high bispectral index in sedated volunteers with high electromyographic activity. They concluded that electromyographic activity could falsely increase the bispectral index, which could be a problem in the absence of muscle relaxants. This does not raise the question of whether awareness during total neuromuscular block is possible despite bispectral index monitoring.
We reported unexpected low bispectral index values in fully awake persons (ourselves) under total neuromuscular block, which in contrast is a problem in the presence of muscle relaxants. This is, in fact, much more threatening. Our trial was the only way to prove that being awake and totally paralyzed despite bispectral index monitoring is possible and was reality in the three reported cases.
Knowing the limitations of the monitoring devices used is essential for providing safety for our patients. Therefore, taking the risk of this trial ourselves seemed to be justified to us and our institutional ethics board.
M. Messner, MD*
U. Beese, MD*
J. Romstöck, MD†
M. Dinkel, MD‡
K. Tschaikowsky, MD*
Departments of *Anesthesiology and †Neurosurgery
‡Department of Anesthesiology
Herz- und Gefäβ-Klinik
Bad Neustadt/Saale, Germany
1. Messner M, Beese U, Romstock J, et al. The bispectral index declines during neuromuscular block in fully awake persons. Anesth Analg 2003;97:488–91.
2. Bruhn J, Bouillon TW, Shafer SL. Electromyographic activity falsely elevates the bispectral index. Anesthesiology 2000;92:1485–7.