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BIS-Related Research Highlights from the 2002 ASA Annual Meetingby Paul Manberg, PhD Over the past decade, we have witnessed a definite evolution in the scope of research studies involving new brain monitoring technologies such as BIS. As the utilization of BIS monitoring has become more widespread, research is no longer limited to the small group of academic investigators interested in better defining the pharmacokinetic and pharmacodynamic properties of propofol and the various opioid analgesics. In looking over the variety of studies to be presented at this year’s annual meeting, it is clear that brain monitoring of anesthetic response has now become an integral component of many research projects. While it is difficult to summarize all of the interesting findings that will be presented, several major themes emerge. Defining anesthetic state Many studies this year have utilized BIS, along with standard parameters (i.e. blood pressure, heart rate, administered dose), as a validation tool to help define the comparable clinical state of subjects enrolled in various trials. Perhaps the most interesting of these studies are two trials reporting on the efficacy of a new anesthetic drug called AQUAVAN® (a water-soluble Pro-drug of Propofol being developed by Guilford Pharmaceuticals Vanluchene A-455, Fechner A-438) and another on DSIP, an endogenous sleep-inducing peptide (Pomfrett – A-579). In the past, relative potency of these agents might have been defined primarily on a comparison of doses required to suppress movement at incision or initial loss of responsiveness following induction. Now, a more comprehensive profile of the pharmacodynamic response to these new anesthetics can be described using BIS as a measure of drug effect. Use of BIS as an objective, quantitative measure of anesthetic state has also provided new insight into the individual responses to anesthetics in special patient populations. For example, this year at least 10 studies describe the BIS response to sevoflurane, isoflurane, propofol or combined general/epidural anesthesia in infants and children. In total, these studies further demonstrate how BIS provides an appropriate dose-response measure in children, and that variability in patient response to a given dose is significant. One interesting paper also utilized BIS response as a marker for hypoperfusion (Hayashida A-1283), thereby suggesting how vigilance to rare, but potentially devastating unexpected cerebral depression can be enhanced with routine monitoring. In addition, several studies describe the unique drug response characteristics of the elderly, as well as differences between men and women – highlighting the complexity of accurately estimating anesthetic requirements based solely on demographic information or cardiovascular response. Individualized dosing based on monitoring a pharmacodynamic measure such as BIS helps account for one component of this inter-patient variability. Alternative brain monitoring methods The growing adoption of brain monitoring with BIS has resulted in the commercial introduction of BIS modules as well as a number of competitive consciousness monitoring products. Results from several preliminary BIS comparison studies will be presented at this year’s meeting and more are sure to follow in the future as clinicians seek to determine the most useful product to buy. It is interesting to observe how the debate has shifted from “is neuromonitoring (with BIS) effective” to “which technology works best.” I would contend that the extensive published clinical validation of BIS monitoring in diverse populations (children, adults, elderly), the outcome experience in over 5.5 million cases, and the availability of BIS in many standard multiparameter monitoring systems provides a compelling case for BIS, which has yet to be matched by any other competing technology in this field. Cost-benefit considerations Several posters being presented this year introduce some simple cost-benefit calculations that administrators may consider prior to acquisition of BIS monitoring. Abenstein (A-548 and 577), expanding on comments made at a special STA panel debate last year, describes how savings associated with either drug savings alone, or reduction in awareness episodes alone, probably do not adequately offset the added material costs of BIS monitoring at this single institution. Taken in isolation, monitoring with BIS would thus not seem to be cost-effective in this narrow financial context. Of course, a more comprehensive analysis including all of the documented outcome benefits associated with BIS monitoring might reach a more favorable conclusion. Your local Aspect representative would welcome the opportunity to provide additional information in this regard. BIS and procedural sedation The expanding use of BIS in routine clinical practice is reflected in several studies (A-473, A-438, A-6) describing use in procedural sedation with propofol. All three show a strong BIS correlation with the clinical OAA/S scale and patient response to the procedure. In August 2002, Aspect announced a strategic partnership with Boston Scientific to jointly develop new monitoring products for these applications (see “What’s New at Aspect” on pg 2). Age, anesthetic levels and mortality Perhaps the most provocative study (Weldon A-1097) to be presented this year is a relatively large (n=907) prospective study that determined demographic and surgical factors that were associated with one-year mortality following major, non-cardiac surgery. The conclusion presented in the abstract was that “deeper maintenance anesthetic levels were associated with higher one-year death rates in patients 40 years and older.” Undoubtedly, many factors contribute to long term patient outcomes and this important finding needs to be confirmed in additional trials. Nonetheless, this initial study underscores the concept that optimum anesthetic management can have dramatic impact on patient outcomes, especially in the elderly population. This also reinforces the important role that brain monitoring has played in modern anesthesia research. |
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