SAQ 2017.2 Question 4

Describe the generation and features of a normal awake EEG (15)

Briefly discuss the processing performed by EEG monitors (BIS/Entropy) to produce a single dimensionless number from the EEG (10)

This material is adequately covered in a couple of the books on the recommended reading list – Magee & Tooley, and Davis & Kenny. There are some better review articles around, and a mob of FANZCAs in Cairns paralysed each other sans anaesthesia using BIS monitoring and published it (British Journal of Anaesthesia, Volume 115, Issue suppl_1, 1 July 2015, Pages i95–i103).

The EEG measures action potentials     TRUE/FALSE

As a patient becomes more deeply anaesthetised their EEG drops in amplitude and frequency    TRUE/FALSE

Burst suppression becomes more pronounced with deeper levels of anaesthesia    TRUE/FALSE

Phase coherence becomes more pronounced with deeper levels of anaesthesia    TRUE/FALSE

Frowning will increase RE (response entropy) more than SE (state entropy)    TRUE/FALSE

Depth of anaesthesia monitoring…again

BT_GS 1.52 Explain the principles involved in the electronic monitoring of depth of sedation and anaesthesia, including the use of EEG analysis

Again, the comments relate to the beloved BIS again.

BIS has been validated as a depth of anaesthesia monitor in large clinical trials  T/F

Burst suppression is seen in physiological sleep  T/F

Propofol can cause an isoelectric EEG  T/F

Volatile anaesthetics can suppress the EEG but not cause an isoelectric EEG  T/F

Spindle formation on the EEG is only seen in slow wave sleep  T/F

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 ICETAP.org 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