To the Editor:—

We read with interest the recent article by O'Connor et al.  1regarding the lack of cost effectiveness of the Bispectral Index (BIS)®monitor (Aspect Medical Systems, Natick, MA) when used to prevent awareness during general anesthesia. In arriving at their conclusion that the BIS®monitor is an expensive way to prevent awareness during anesthesia, the authors admonished that their cost effectiveness analysis was justified only if the BIS is used solely to reduce the risk of awareness. Also of interest, in the same issue of the Journal, is the article by Röpcke et al. , 2which examines the concentration–response relation of desflurane to the electroencephalogram as measured by the BIS during surgical stimulation. This article, along with many others, 3–6clearly shows that the BIS has a much broader application in anesthesia practice than solely to prevent awareness.

To use the BIS®monitor only for the purpose of preventing awareness would be comparable with using a blood pressure monitor to prevent hypertension: it is too limited in scope and too narrow in its focus. Blood pressure monitoring allows one to gauge the response of the sympathetic nervous system to anesthesia, surgery, and other intraoperative factors. It is useful over a wide range of values in helping the practitioner to make decisions regarding the care of the patient. The value provided by the monitor must be interpreted in the context of the clinical situation. Similarly, the BIS®monitor measures the response of the frontal electroencephalogram to anesthetics as influenced by surgical stimulation and other conditions. Analogous to the blood pressure measurement, any given BIS value must be interpreted in the light of the clinical scenario. One cannot make an appropriate interpretation if the value is taken out of context of the patient's condition.

The question of whether the BIS®monitor is cost effective in general must await the determination of its overall usefulness. The BIS®monitor is the first broadly applicable clinical tool to measure and transform the electroencephalogram into a readily interpretable form that correlates with anesthetic dosage and measures the individual patient response to anesthetics. Given the current growth of information about pharmacogenomics 7and the importance of individualizing dosages and drugs, any device that allows us to monitor the unique response that each patient has to varying anesthetic doses will be useful. We hope that articles such as that by O'Connor et al.  1with their rather narrow focus will not provide the justification for those readers who would hastily dismiss, without further investigation, the potential of new devices such as the BIS®monitor.

O'Connor MF, Daves SM, Tung A, Cook RI, Thisted R, Apfelbaum J: BIS monitoring to prevent awareness during general anesthesia. A nesthesiology 2001; 94: 520–2
Röpcke H, Rehberg B, Koenen-Bergmann M, Bouillon T, Bruhn J, Hoeft A: Surgical stimulation shifts EEG concentration–response relationship of desflurane. A nesthesiology 2001; 94: 390–9
Struys M, Versichelen L, Byttebier G, Mortier E, Moerman A, Rolly G: Clinical usefulness of the bispectral index for titrating propofol target effect-site concentration. Anaesthesia 1998; 53: 4–12
Yli-Hankala A, Vakkuri A, Annila P, Korttila K: EEG bispectral index monitoring in sevoflurane or propofol anaesthesia: Analysis of direct costs and immediate recovery. Acta Anaesthesiol Scand 1999; 43: 545–9
Hans P, Bonhomme V, Born JD, Maertens de Noordhoudt A, Brichant JF, Dewandre PY: Target-controlled infusion of propofol and remifentanil combined with bispectral index monitoring for awake craniotomy. Anaesthesia 2000; 55: 255–9
Kazama T, Ikeda K, Morita K, Kikura M, Doi M, Ikeda T, Kurita T, Nakajima Y: Comparison of the effect-site keOs of propofol for blood pressure and EEG bispectral index in elderly and younger patients. A nesthesiology 1999; 90: 1517–27
Rusnak JM, Kisabeth RM, Herbert DP, McNeil DM: Pharmacogenomics: A clinician's primer on emerging technologies for improved patient care. Mayo Clin Proc 2001; 76: 299–309