To the Editor:—

I read with great interest the exchange of opinions regarding “The Media and the BIS Monitor,” which appeared in the June issue of ANESTHESIOLOGY. 1,2The letters highlighted some very important issues facing anesthesiologists and Aspect Medical Systems, especially in today’s healthcare environment.

As you indicated in your response to Dr. Katz, Aspect has been very careful about not making specific claims that use of the BIS will reduce the incidence of intraoperative recall. We state in our marketing materials that the BIS Monitor can be used as a tool to “monitor,”“assess,” or “track” the risk of awareness based on results from numerous peer-reviewed publications demonstrating the relationship between BIS and sedation scores, memory function tests, and loss and return of consciousness in volunteers and surgical patients. 3–13It is not our intention to suggest that these studies prove that BIS monitoring will reduce the incidence of awareness. In fact, it is very important for anesthesiologists to understand that awareness can still occur when BIS monitors are used, although we believe the data clearly support the observation that awareness is most likely to happen when BIS values are high.

Widespread publicity of awareness cases on national television, news magazines, and newspapers with the resulting reactions of the anesthesia community have represented a significant public relations challenge to Aspect. Our efforts to introduce the BIS to the anesthesia community have relied extensively on sound clinical research published in high-quality journals such as ANESTHESIOLOGY. To date, more than 45 full manuscripts and more than 300 abstracts have been published on BIS. Our sales and marketing programs have always highlighted the demonstrated drug savings and recovery benefits of BIS rather than focusing on prevention of awareness. The perceived benefit to Aspect from awareness-related publicity is overshadowed by the negative impact it has had on our relationship with the anesthesia community, which we have worked so hard to build over the past 13 yr. The letter from Dr. Katz is a good case in point.

I sincerely hope that this letter provides a better understanding of Aspect’s position regarding the issue of awareness and BIS. Perhaps some day it will be possible to conduct a definitive clinical study to evaluate the impact of BIS monitoring on the incidence of awareness (although such a study would require randomization of approximately 50,000 patients to have adequate statistical power* ), but until then, the potential efficacy of BIS monitoring in preventing awareness can only be reasonably inferred from the previously cited references. The scientifically demonstrated recovery benefits of BIS monitoring provide the most important reasons for anesthesia providers to consider using this technology.

1.
Katz SM: The media and the BIS monitor (letter). A NESTHESIOLOGY 1999; 90:1796
2.
Todd MM: The media and the BIS monitor (reply). A NESTHESIOLOGY 1999; 90:1797
3.
Kearse L, Rosow C, Zaslavsky A, Connors P, Dershwitz M, Denman W: Bispectral analysis of the electroencephalogram predicts conscious processing of information during propofol sedation and hypnosis. A NESTHESIOLOGY 1998; 88:25–34
4.
Glass PS, Bloom M, Kearse L, Rosow C, Sebel P, Manberg P: Bispectral analysis measures sedation and memory effects of propofol, midazolam, isoflurane, and alfentanil in healthy volunteers. A NESTHESIOLOGY 1997; 86:836–47
5.
Flaishon R, Windsor A, Sigl J, Sebel PS: Recovery of consciousness after thiopental or propofol. A NESTHESIOLOGY 1997; 86:613–9
6.
Katoh T, Suzuki A, Ikeda K: Electroencephalographic derivatives as a tool for predicting the depth of sedation and anesthesia induced by sevoflurane. A NESTHESIOLOGY 1998; 88:642–50
7.
Lubke GH, Kerssens C, Phaf H, Sebel PS: Dependence of explicit and implicit memory on hypnotic state in trauma patients. A NESTHESIOLOGY 1999; 90:1–12
8.
Leslie K, Sessler DI, Schroeder M, Walters K: Propofol blood concentrations and the bispectral index predict suppression of learning during propofol/epidural anesthesia in volunteers. Anesth Analg 1995; 81:1269–74
9.
Doi M, Gajraj RJ, Mantzaridis H, Kenny GNC: Relationship between calculated blood concentration of propofol and electrophysiological variables during emergence from anaesthesia: Comparison of bispectral index, spectral edge frequency, median frequency and auditory evoked potential index. Br J Anaesth 1997; 78:180–4
10.
Liu J, Singh H, White PF: Electroencephalographic bispectral index correlates with intraoperative recall and depth of propofol-induced sedation. Anesth Analg 1997; 84:185–9
11.
Gan TJ, Glass PS, Windsor A, Payne F, Rosow C, Sebel P, Manberg P, the BIS Utility Study Group: Bispectral index monitoring allows faster emergence and improved recovery from propofol, alfentanil, and nitrous oxide anesthesia. A NESTHESIOLOGY 1997; 87:808–15
the BIS Utility Study Group
12.
Iselin-Chaves A, Flaishon R, Sebel P, Howell S, Gan TJ, Sigl J, Ginsberg B, Glass P: The effect of the interaction of propofol and alfentanil on recall, loss of consciousness, and the bispectral index. Anesth Analg 1998; 87:949–55
13.
Olofsen E, Dahan A: The dynamic relationship between end-tidal sevoflurane and isoflurane concentrations and bispectral index and spectral edge frequency of the electroencephalogram. A NESTHESIOLOGY 1999; 90:1345–53