We thank Dr. Bischoff et al. for their interest in our study on Narcotrend (MonitorTechnik, Bad Bramstedt, Germany) and Bispectral Index® (BIS®; Aspect Medical Systems Inc., Newton, MA) monitoring used for guidance of propofol titration during propofol–remifen tanil anesthesia. 1The results of our study indicate that compared with standard practice, patients with Narcotrend or BIS monitoring needed significantly less propofol, opened their eyes earlier, and were extubated sooner.
Bischoff et al. now discuss the possibility of an increased risk of memory function resulting in potential awareness if electroencephalographic monitoring is used to optimize recovery times and drug consumption. They do so especially in view of our study design, which included a lightening of anesthesia during the last 15 min before the end of surgery to a target value of C1for Narcotrend or 60 for BIS®.
Now, three questions must be discussed: First, should electroencephalographic monitoring in principle be used to fast track anesthesia; second, does monitoring of the depth of anesthesia result in an increased risk of awareness; and third, is it adequate to lighten anesthesia at the end of surgery?
First, electroencephalographic monitoring is a valuable tool to fast-track anesthesia. Several studies, including ours, 1–3have shown that monitoring the depth of anesthesia clearly reduces the guesswork regarding how much of the anesthetic is necessary for the individual patient. Thus, this monitoring allows for individual titration of anesthesia, resulting in a reduction of drug consumption and recovery times.
Second, Myles et al. 4have now brought some light to the discussion about the impact of electroencephalographic monitoring on the risk of awareness. In their investigation, 1,227 patients were randomly assigned to a BIS-guided anesthetic protocol with BIS target values of 40–60, and 1,238 patients received “routine care,” with no electroencephalographic monitoring information available. With this study design, Myles et al. observed 2 cases of awareness in the BIS® group and 11 in the standard practice group (P < 0.022). Therefore, BIS-guided anesthesia reduced the risk of awareness by 82% and was also associated with a decreased time to eye opening.
Third, lightening of anesthesia at the end of surgery has been standard of care for many years without electroencephalographic monitoring. In particular, in our study, we used target values of 60 for BIS® (being within the study range of Myles et al. ) and C1for the Narcotrend. In a previous investigation, BIS values of 60 were matched to Narcotrend stages of C1, 5and therefore, these results were used as target values for the guidance of propofol titration in our investigation.
In conclusion, we are convinced that it is possible to optimize recovery times, reduce drug consumption, and have a lower risk of awareness by using electroencephalographic monitoring during general anesthesia.