To the Editor:—
Although it is not discussed by O'Connor et al. 1in their recent article, the scientific literature about pulse oximetry is perhaps more pertinent to the use of Bispectral Index (BIS) monitoring than screening preoperative chest films, the straw man they erect in their argument. Specifically, the studies by Moller et al. 2,3of more than 20,000 patients failed to show an effect on “cardiovascular, respiratory, neurologic or infectious” outcomes (including death) or length of hospital stay from the use of pulse oximetry. However, in responses to a questionnaire administered to anesthesiologists taking part in the study, 80% of anesthesiologists said that they felt more “secure” using pulse oximetry, and 18% said that pulse oximetry had helped them to manage a particular incident during an anesthetic procedure. In their editorial accompanying these studies, Orkin et al. 4comment, “While aids to vigilance cannot independently engender greater safety (i.e. , improved outcome) their use provides comforting backup to clinical observation, allows dedication of attention to other matters and reassures our fallible reasoning with online data during critical periods of the anesthetic.”
Bispectral Index monitoring, like pulse oximetry, is an “aid to vigilance.” By itself, it cannot prevent or treat awareness during anesthesia. However, a quick glance at the BIS®monitor (Aspect Medical Systems, Natick, MA) to confirm that it is overwhelmingly likely that the patient is asleep during a period of tachycardia or increased blood pressure permits the anesthesiologist to quickly focus her or his attention elsewhere. The comment of O'Connor et al. 1that “there are cases of awareness in the Aspect database” is clarified, in this context, by the fact that there are no cases of awareness in the Aspect database with a BIS measurement lower than 65. 5Should BIS monitoring be made a standard of practice in anesthesia? The arguments for and against are no more powerful than they are for pulse oximetry.