Investors Have Overreacted: The Use of BIS Devices to Monitor the Depth of Anesthesia Will Not Be Affected by One Negative Article

Implications: The recent study in the New England Journal of Medicine has suggested that the BIS monitoring system does not reduce the incidence of awareness under anesthesia. The stock of Aspect Medical Systems, the manufacturer of the BIS monitoring system, has lost 40% of its value during the last few weeks. The numerous problems with this particular trial design and its execution, however, preclude the educated reader from drawing any far-reaching conclusions. I do not believe that this article would seriously affect the use of BIS devices.

Analysis:  Recall of intraoperative events is an infrequent (0.2%), but well described, complication of general anesthesia. It may lead to posttraumatic stress syndrome. The Joint Commission on the Accreditation of Healthcare Organizations (JCAHO) as well as the American Society of Anesthesiologists (ASA) has issued guidelines with respect to the monitoring of this complication. BIS was approved by the FDA in 2003 as a parameter that could help to control awareness incidence in the patient. Three large clinical trials have documented the advantages of using brain function monitoring in reducing the incidence of intraoperative awareness. However, some anesthesiologists, despite the widespread use of brain function monitoring devices, have questioned the utility of this technology in reducing the incidence of awareness. The study in NJEM was designed to show that the BIS system does not reduce the incidence of awareness when compared with an anesthetic guided by maintaining a high concentration of inhalational anesthetic. There are several problems with the design and execution of the study, the most serious of which are: 1. The BIS recordings of two patients who had a definite recall of intraoperative events are incomplete; the conclusion of the study is based exclusively on these two recordings; 2. A record of one patient who was judged to have a possible recall indicates that the BIS readings were ignored; 3. The study does not have adequate power to support the authors’ conclusions; 4. The authors have used a rather arbitrary criteria to select patients at  “high risk for anesthesia awareness”. Considering the limitations of the study, I believe that most anesthesiologists would ignore the conclusion of this article.