When the BIS was first marketed in 1996, only the BIS values were trended horizontally on the screen. Sadly, this left users with the option of trying to drive their 'car' (titrate anesthetic) with the 'rear view mirror' (information delayed from real time ). The net effect was that when things were going along steadily, all of a sudden the patient would wake up.
The electrical signal of the frontalis muscle (EMG) was not originally trended for fear it would 'contaminate' the BIS signal. When Aspect sent their people to observe my use of trending EMG as the secondary signal, they invariably commented 'I've never seen anyone use the device this way.' To which I replied, 'No one uses a tool that is not useful.'
The EMG of the frontalis muscle is like the EKG of the heart muscle, a real time, useful signal. The 'contamination' of the EMG spike is telling you, 'Hey dude, I am about to wake up unless you intervene!' There is no all of a sudden when EMG provides an early warning signal.
The EMG on the VISTA model is in red. When the red (EMG) goes up, the white (propofol) goes in... until RMG is returned to baseline, preferably not so high a dose(s) that spontaneous ventilation is eliminated in my paradigm. I typically use 200-400 mcg/kg propofol doses repeated to effect.
FWIW, the current factory default has the EMG pre-set as the secondary trend to BIS. The plug in modules do not have this option, only the free standing ones. It also works for the monchrome A-2000.
Dr. Friedberg's answer is spot on. My only addition would be that Bis is a very poor predictor of patient movement in response to stimuli, as such movement is cord mediated rather than centrally mediated. Thus, in the absence of neuromuscular blockade, patients may exhibit Bis signs of adequate hypnosis while moving in response to surgical stimulus. We did some research concerning implicit memory formation during anesthesia in which we used the bis monitor, and some of the background information in the article might be of use, see attached.
All the best
Rich
Bis corresponds fairly when sedation as hypnosis as well as cognitive functions following GA when BIS value is more than 85. It is a useful tool but new generation -measuring bilateral is better option
Appreciate your response Dr. Singh. Any literature in support would be appreciated.
4 years after your question... I would change the question to " How does one make EEG a useful, real time intraoperative monitor?"
BIS was indeed the first processed EEG monitor launched to help anesthesiologists to guide anesthesia, a real advance in our practice but two decades after, I think we have to move to a different way to brain monitoring during anesthesia and sedation.
Knowing the different signatures of anesthetic drugs in EEG we should look to the raw EEG and spectral analysis more than to a dimensionless scale with several limitations ( doi: 10.1097/ACO.0b013e32834c7aba) as very well reviewed by Purdon et al (doi: 10.1097/ALN.0000000000000841), Montupil (doi: 10.1053/j.jcva.2019.03.038) and justified by us (doi: 10.1053/j.jcva.2019.03.037).
Also, we should have a monitor with specific features like the possibility to change the scale of EEG amplitude and the scale of spectrogram scale).
Dr. Lobo: different anesthetic agents project different EEG patterns. Prior to BIS, intraoperative EEG monitoring was cumbersome, expensive & impractical.
The brilliance of the BIS algorithm was unifying inhalation & intravenous agents into a single paradigm. That said, BIS values alone are not predictive of patient movement. Real time EMG spikes ARE predictive. Lets not rush to abandon technology validated in >3,500 published studies but rather learn to use the existing technology to its greatest patient benefit. 🙏