BIS Monitoring

BT GS 1.52 Explain the principles involved in the electronic monitoring of depth of anaesthesia, including the use of EEG analysis.

The statements relate to BIS as this is the most commonly used ‘depth of anaesthesia’ monitor in Australasia. Entropy is pretty similar. A plea from a pragmatic anaesthetist- if you are going to use BIS then please make sure you are displaying the EEG trace on your monitor (and make sure you’ve turned the filter off). The dimensionless number by itself is close to useless. You should be able to interpret a raw EEG trace as well as you can an arterial waveform or ECG trace. I highly commend the website as an educational resource. It is an excellent place to learn how to interpret the EEG and get the most clinically useful information from your processed EEG monitor. If you don’t know the answer to the third statement below then can I suggest you look at the paper by Whitlock et al in Anesthesiology 2011; 115: 1209-18. Figure 4 should astonish you if you haven’t already seen it.

The algorithm by which the BIS value is calculated has been made known to clinicians T/F

Ketamine can elevate the BIS reading because of its effect on the beta ratio  T/F

There is a clear dose-response relationship between BIS values and end-tidal volatile concentrations  T/F

There is a clear dose-response relationship between BIS values and plasma propofol concentrations  T/F

SR denotes the Suppression ratio which is the percentage of time in the preceding 63s that the EEG has been suppressed. T/F


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